Name: comparison of two different synthesis methods of single crystals of superconducting uranium ditelluride
Uploaded: 2021-07-08T14:00:00.000+00:00
Duration: 4 min 51 s
Description: Watch this Scientific Journal Video about Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride at JoVE.com

This research was supported by the National Institute of Standards and Technology. Portions of the synthesis were supported by Gordon and Betty Moore Foundation&#39;s EPiQS Initiative through Grant No. GBMF9071. Portions of the characterization were supported by the US Department of Energy (DOE) award DE-SC0019154. Identification of certain commercial products and company names is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the products or names identified are necessarily the best available for the purpose.

1. Removing uranium oxide from the uranium metal
<ol>
	<li>In a fume hood, prepare three beakers that contain 1 mL of nitric acid, 5 mL of distilled water, and 5 mL of acetone, respectively.</li>
	<li>Using a saw or cutters, cut a piece of uranium metal to the desired mass.</li>
	<li>Using tweezers, place the uranium into the beaker with nitric acid. Wait for approximately 10 s for the acid to dissolve the black oxidized surface, such that the uranium appears shiny and metallic.</li>
	<li>Take out the piece of uranium from the acid, rinse it in distilled water for 5 s, and then remove the piece of uranium.</li>
	<li>Put the uranium into the beaker containing acetone for 5 s and remove it.</li>
	<li>Determine the mass of the uranium. The uranium is ready for synthesis.</li>
</ol>
2. Chemical vapor transport
<ol>
	<li>Weigh out an appropriate amount of elemental tellurium, depending on the amount of uranium previously cleaned, following an atomic ratio of uranium to tellurium of 2:3.</li>
	<li>Weigh out an appropriate amount of iodine, determined by the desired density of 1 mg/cm3 in the volume of the quartz tube to be used during synthesis. Choose a length of the tube to span the furnace, with each end sitting in one of the temperature zones. Ensure that the diameter fits well in the furnace. 
	NOTE: Samples previously reported3 were made in a quartz tube that is 11 cm long, with a 14 mm inner diameter, so that the total mass of iodine is about 17 mg.</li>
	<li>Close one end of a fused quartz tube using a torch. A hydrogen/oxygen torch works well. Use any torch that gets hot enough to soften fused quartz. Allow the tube to cool.</li>
	<li>Put all the materials into the quartz tube. Evacuate the tube using a dry vacuum pump and seal the tube with the torch.</li>
	<li>Insert the tube into a 2-zone horizontal tube furnace. When doing this, make sure to slide all the raw materials to one side of the tube, which will be the hot side.</li>
	<li>Over 12 h, heat at constant rates the hot side to 1060 &#176;C, and the other side to 1000 &#176;C. Hold the temperatures for 1 week, and then turn off the furnace to allow it to cool slowly to room temperature.</li>
</ol>
3. Molten metal flux growth
<ol>
	<li>Weigh out uranium and tellurium according to the atomic ratio of 1:3.</li>
	<li>Put all the materials in a 2 mL alumina crucible. On top of this crucible, place another 2 mL crucible, filled with quartz wool, facing downward.</li>
	<li>Close one end of a fused quartz tube using a torch. A hydrogen/oxygen torch works well. Use any torch that gets hot enough to soften the fused quartz. Allow the tube to cool.</li>
	<li>Place the two crucibles into a quartz tube having a 14 mm inner diameter. Use a dry vacuum pump to evacuate the tube and then seal the tube with the torch.</li>
	<li>Put the quartz tube into a 50 mL alumina crucible to be used as an exterior container for stability. Place these in a box furnace.</li>
	<li>Over 12 h, heat the furnace at a constant rate to 1180 &#176;C. Hold the temperature for 5 h. Cool the furnace at constant rate to 975 &#176;C for over 100 h.</li>
	<li>Prepare a centrifuge with a swing out rotor and metal buckets. At 975 &#176;C, take out the tube using furnace tongs, carefully invert it, and then put it into the centrifuge. Spin at 2500 x g (4000 rpm for these sealed quartz tube assemblies) for 10-20 s, forcing the extra liquid tellurium to separate from the UTe2 crystals and get caught in the quartz wool.</li>
	<li>Allow the tube to cool to room temperature.</li>
</ol>
4. Opening the tubes and harvesting the crystals
<ol>
	<li>Place the quartz tube into a sealed plastic bag and place it on a hard surface, such as a laboratory benchtop or a fume hood.</li>
	<li>Using a small hammer or any other blunt object, carefully crack and break the quartz tube, preferably at the end away from the crystals.</li>
	<li>Open the plastic bag and pick out the UTe2 crystals. Perform this process within an hour or so, as UTe2 is air-sensitive and noticeably degrades over the course of several hours.</li>
	<li>Rinse the crystals with 2 mL of ethanol to remove iodine.</li>
	<li>Store the UTe2 crystals under an inert atmosphere, such as inside a nitrogen glove box.</li>
</ol>

<ol>
	<li>Sau, J. D., Tewari, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Topologically+protected+surface+majorana+arcs+and+bulk+weyl+fermions+in+ferromagnetic+superconductors.">Topologically protected surface majorana arcs and bulk weyl fermions in ferromagnetic superconductors.</a> Physical Review B. 86 (10), 104509 (2012).</li><li>Fu, L., Kane, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superconducting+proximity+effect+and+majorana+fermions+at+the+surface+of+a+topological+insulator.">Superconducting proximity effect and majorana fermions at the surface of a topological insulator.</a> Physical Review Letters. 100 (9), 096407 (2008).</li><li>Ran, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nearly+ferromagnetic+spin-triplet+superconductivity.">Nearly ferromagnetic spin-triplet superconductivity.</a> Science. 365 (6454), 684-687 (2019).</li><li>Hayes, I. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Weyl+Superconductivity+in+UTe2.">Weyl Superconductivity in UTe2.</a> arXiv. , (2020).</li><li>Jiao, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chiral+superconductivity+in+heavy-fermion+metal+UTe2.">Chiral superconductivity in heavy-fermion metal UTe2.</a> Nature. 579, 523 (2020).</li><li>Ran, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extreme+magnetic+field-boosted+superconductivity.">Extreme magnetic field-boosted superconductivity.</a> Nature Physics. 15, 1250-1254 (2019).</li><li>Aoki, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unconventional+superconductivity+in+heavy+fermion+UTe2.">Unconventional superconductivity in heavy fermion UTe2.</a> Journal of the Physical Society of Japan. 88, 043702 (2019).</li><li>Cairnsm, L. P., Stevensm, C. R., O'Neill, C. D., Huxley, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Composition+dependence+of+the+superconducting+properties+of+UTe2.">Composition dependence of the superconducting properties of UTe2.</a> Journal of Physics. Condensed Matter: An Institute of Physics Journal. 32 (41), 415602 (2020).</li><li>Thomas, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+a+pressure-induced+antiferromagnetic+quantum+critical+point+in+mixed+valence+UTe2.">Evidence for a pressure-induced antiferromagnetic quantum critical point in mixed valence UTe2.</a> Science Advances. 6 (42), (2020).</li><li>Hutanu, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-temperature+crystal+structure+of+the+unconventional+spin-triplet+superconductor+UTe2+from+single-crystal+neutron+diffraction.">Low-temperature crystal structure of the unconventional spin-triplet superconductor UTe2 from single-crystal neutron diffraction.</a> Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials. 76, 137-143 (2020).</li><li>Sundar, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coexistence+of+ferromagnetic+fluctuations+and+superconductivity+in+the+actinide+superconductor+UTe2.">Coexistence of ferromagnetic fluctuations and superconductivity in the actinide superconductor UTe2.</a> Physical Review B. 100, 140502 (2019).</li><li>Metz, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Point-node+gap+structure+of+the+spin-triplet+superconductor+UTe2.">Point-node gap structure of the spin-triplet superconductor UTe2.</a> Physical Review B. 100, 220504 (2019).</li><li>Knebel, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Field-reentrant+superconductivity+close+to+a+metamagnetic+transition+in+the+heavy-fermion+superconductor+UTe2.">Field-reentrant superconductivity close to a metamagnetic transition in the heavy-fermion superconductor UTe2.</a> Journal of the Physical Society of Japan. 88, 063707 (2019).</li><li>Braithwaite, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+superconducting+phases+in+a+nearly+ferromagnetic+system.">Multiple superconducting phases in a nearly ferromagnetic system.</a> Communications Physics. 2, 147 (2019).</li><li>Ran, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+and+reentrance+of+spin+triplet+superconductivity+in+UTe2+under+pressure.">Enhancement and reentrance of spin triplet superconductivity in UTe2 under pressure.</a> Physical Review B. 101, 140503 (2020).</li><li>Nakamine, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superconducting+properties+of+heavy+fermion+UTe2+revealed+by+125Te-nuclear+magnetic+resonance.">Superconducting properties of heavy fermion UTe2 revealed by 125Te-nuclear magnetic resonance.</a> Journal of the Physical Society of Japan. 88, 113703 (2020).</li><li>Miao, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+energy+band+structure+and+symmetries+of+UTe2+from+angle+resolved+photoemission+spectroscopy.">Low energy band structure and symmetries of UTe2 from angle resolved photoemission spectroscopy.</a> Physical Review Letters. , 124 (2020).</li><li>Lin, W. -. 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The authors declare no competing interests.

To perform chemical vapor transport, it is simplest to utilize a two-zone horizontal furnace, which can generate a temperature gradient by setting the two zones at different temperatures. Successful use of a one-zone furnace to grow superconducting samples has not yet been demonstrated. Starting materials are sealed with a hydrogen-oxygen torch in a fused quartz tube, which must be purged of air. The purging and sealing can be accomplished by connecting the tube to a manifold attached to a dry pump and an argon gas cylinder. Once prepared, this tube is placed in the furnace such that two ends of the tube span the two temperature zones. In the case of UTe2, the end of the tube containing the starting materials is placed at the hot end. The elemental uranium and tellurium react with iodine, travel down the tube as a vapor, and eventually solidify at the cold end the quartz tube in the form of single crystals. Generally, the growth of large crystals is material-dependent and can take several weeks. For UTe2, 7 days is enough to grow crystals with mm dimensions. Following the growth, the tube is removed from the furnace and opened to harvest the crystals.
The molten metal self-flux method requires a simple resistive box furnace with one temperature zone. Uranium dissolves in molten tellurium, and the solubility of UTe2 is dependent on temperature. Starting materials, elemental uranium, and tellurium, are placed in an alumina crucible. On top of this crucible, a second crucible is placed upside down, filled with quartz wool. The two crucibles are sealed in a quartz tube, which is put in a box furnace. This time, instead of generating a fixed temperature gradient over a distance, the temperature is varied as a function of time, as the furnace is slowly cooled at a fixed rate. At the highest temperature, all the uranium will be dissolved in liquid tellurium, which has a much lower melting temperature than uranium. As the furnace cools, the solubility of UTe2 decreases and UTe2 single crystals precipitate and get larger. At a temperature that is low enough to have generated sufficiently large UTe2 single crystals, but still high enough for the tellurium to remain liquid, the quartz tube is removed from the hot furnace, placed it into a centrifuge and spun, which separates the solid UTe2 from the liquid tellurium before it freezes. After that, the tube is allowed to cool to room temperature, before it is broken to collect the crystals.
Working with depleted uranium is a heavily regulated activity that requires awareness of and compliance with applicable laws. Follow all local applicable hazardous and radioactive materials safety rules, and secure necessary permission to perform this work. These rules vary by jurisdiction and institution and cannot be addressed here. However, some general principles apply that can help with the planning of research. Researchers should be trained to work with radioactive and hazardous materials. Wear necessary personal protective equipment, including gloves. Work methodically and take care to avoid the spread of radioactive material. Discard waste in labeled and approved containers.

At temperatures typically much lower than room temperature, many materials exhibit superconductivity-the fascinating macroscopic quantum state in which the electrical resistance becomes absolutely zero and electrical current can flow without dissipation. In the typical superconducting phase, instead of acting as separate entities, the constituent electrons form Cooper pairs, which are commonly made up of two electrons with opposite spins, in a spin singlet configuration. However, in very rare cases, the Cooper pairs can instead be made up of two electrons with parallel spins, in a spin triplet configuration. Among the few thousand superconductors discovered so far, there are only a few superconductors that have been identified as spin triplet candidates. This rare quantum phenomenon has attracted a lot of research interest because spin triplet superconductors are proposed to be one potential building block for quantum computers1,2, the next generation of computation technology.
Recently, Ran and coworkers reported that UTe2 is a candidate spin triplet superconductor3. This superconductor has many exotic properties indicative of a spin triplet configuration: an extreme, disproportionately large, critical magnetic field required to suppress the superconductivity, a temperature-independent NMR Knight shift3, a spontaneous magnetic moment indicated by the optical Kerr effect4, and a chiral electronic surface state indicated by scanning tunneling spectroscopy5. Moreover, additional superconducting phases are actually induced in high magnetic field6, an example of the unusual phenomenon of reentrant superconductivity.
Although these new results are robust, the superconducting properties of UTe2 depend on the synthesis process used by different groups7,8,9. Crystals of UTe2 synthesized using the chemical vapor transport method superconduct below a critical temperature of 1.6 K. In contrast, those grown using the molten flux method have a greatly suppressed superconducting critical temperature or do not superconduct at all. In anticipation of applications such as quantum computing, reliably obtaining crystals that superconduct is highly desirable. Moreover, investigating why nominally similar crystals do not superconduct is also very helpful for understanding the fundamental superconducting pairing mechanism in UTe2, which, while novel and a topic of intense research, must differ significantly from that of conventional superconductors. For these reasons, the two different synthesis methods are complementary and useful to compare. In this paper, two different methods for synthesis of UTe2 are demonstrated and properties of the single crystals from the two methods are compared.

<table><tbody><tr><td>2-zone tube furnace</td><td>MTI Corporation</td><td>OTF-1200X-S-II-25-110</td><td></td></tr><tr><td>Alumina crucible</td><td>Coorstek Inc.</td><td>65530-CN-2-AD-998</td><td>Size = 2 mL</td></tr><tr><td>Box furnace</td><td>MTI Corporation</td><td>KSL-1500X</td><td></td></tr><tr><td>Centrifuge</td><td>Thermo Scientific</td><td>Mo/No: CL2, S/N:42618752</td><td></td></tr><tr><td>Fused quartz tube</td><td>Quartz Scientific</td><td>100014B</td><td>14 mm ID, 16 mm OD, 48&quot; length</td></tr><tr><td>Iodine</td><td>J. T. Baker Inc.</td><td>2208-04</td><td>Sublimed, 99.997% pure,&amp;nbsp; typically approximately 14 mg</td></tr><tr><td>Tellurium</td><td>Alfa Aesar</td><td>42213</td><td>99.9999% pure,&amp;nbsp; Typically approximately 0.5 g</td></tr><tr><td>Uranium</td><td>Dept. of Energy (NBL)</td><td>CRM115</td><td>Uranium (Depleted U&lt;sup&gt;238&lt;/sup&gt;) Metal (0.99977 g U/g).&amp;nbsp; Typically approximately 0.5 g &lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;238&lt;/sup&gt;U = 0 +- 3.6x10&lt;sup&gt;-9&lt;/sup&gt;</td></tr></tbody></table>

comparison of two different synthesis methods of single crystals of superconducting uranium ditelluride

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic unconventional superconductivity, believed to entail spin-triplet electron pairing. A variety in the superconducting properties of UTe2 reported in the literature indicates that discrepancies between synthesis methods yield crystals with different superconducting properties, including the absence of superconductivity entirely. This protocol describes a process to synthesize crystals that exhibit superconductivity via chemical vapor transport, which has consistently exhibited a superconducting critical temperature of 1.6 K and a double transition indicative of a multi-component order parameter. This is compared to a second protocol that is used to synthesize crystals via the molten metal flux growth technique, which produces samples that are not bulk superconductors. Differences in the crystal properties are revealed through a comparison of structural, chemical, and electronic property measurements, showing that the most dramatic disparity occurs in the low-temperature electrical resistance of the samples.

Both growth techniques yield crystals of UTe2 having dimensions on the millimeter length scale. Crystals are shiny, with a metallic luster. The crystal morphology is variable, and intergrowths can occur. Generally, chemical vapor transport and flux grown crystals look similar and are not easily distinguishable by visual inspection, as is evident in Figure 1.
To confirm the crystal structure, powder x-ray diffraction measurements are typically performed on crushed single crystals of both CVT grown and flux grown UTe2 single crystals at room temperature. Single crystals from both growth techniques have the same crystal structure and are single phase, with no sign of impurity phases. Figure 2 shows the collected x-ray diffraction data and a refinement to a body-centered orthorhombic crystal structure with the space group Immm10.
The temperature dependence of the electrical resistance is a typical way to characterize metallic materials. Figure 3 compares the temperature dependence of the electric resistance, normalized to the room temperature value, for samples of UTe2 synthesized using chemical vapor transport and flux methods. These data were collected in a commercial refrigerator system using a standard 4-lead configuration. Above 50 K, both samples show a slight increase of the electrical resistance upon cooling, which is atypical of metals. This behavior is consistent with that caused by scattering of conduction electrons off the uranium atomic magnetic moments, known as the single ion Kondo effect. A broad maximum is also seen in both samples, followed by a drop in resistance due to the onset of Kondo coherence.
A distinct difference between the samples is that the value of the residual resistance, or value of the resistance in the zero-temperature limit, is dramatically larger in the sample synthesized by the flux method. The residual resistance ratio RRR, or the ratio between the resistance value at room temperature and the residual resistance, is approximately 2 for the flux grown sample, which is about 15 times smaller than the RRR value of the chemical vapor transport sample. The greatly reduced RRR of the flux grown sample indicates that there are more crystallographic impurities or defects in the flux grown sample, which are responsible for stronger scattering of the conduction electrons, and hence the higher residual resistance. These values are consistent with previous reports7.
A more dramatic difference is that the flux grown samples do not superconduct. In general, the presence of impurities and defects is detrimental to superconductivity because increased scattering weakens the electron pairing interaction that underlies superconductivity. The effects of disorder may be even more pronounced in UTe2, in which superconductivity is believed to be of the unusual spin triplet variety that is generally more sensitive to pair breaking11,12,13,14,15,16,17,18,19. The effects of disorder and chemistry on superconductivity in UTe2 are still in the early days and are currently an active field of study.
The DC magnetic susceptibility, or magnetization normalized to the applied field, of both flux grown and CVT grown UTe2 look very similar. As shown in Figure 4, in which the data were collected at 1000 Oe in a commercial SQUID magnetometer, the high-temperature magnetic susceptibility shows a paramagnetic response when the magnetic field is applied along the crystallographic a-axis of the samples. At low temperatures, the magnetic susceptibility increases sharply and then shows a slight slope change at ~10 K, likely due to the Kondo coherence. The difference between the magnetic susceptibility curves of the two samples is small and attributable to slight sample misalignment, rendering the two samples indistinguishable to this measurement.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62563/62563fig01.jpg" /> 
Figure 1: Photographs of single crystals of UTe2. (A) flux grown and (B-C) CVT grown. The grids are 1 mm. <a href="https://www.jove.com/files/ftp_upload/62563/62563fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62563/62563fig02.jpg" /> 
Figure 2: Powder Xray diffraction data of CVT grown UTe2. The data shows the good quality of the sample with no visible peaks from impurities. <a href="https://www.jove.com/files/ftp_upload/62563/62563fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62563/62563fig3v2.jpg" /> 
Figure 3: Normalized electrical resistance data as a function of temperature for both CVT grown and flux grown UTe2. The flux grown sample has a substantially larger residual resistance, which is a signature of increased crystallographic disorder. <a href="https://www.jove.com/files/ftp_upload/62563/62563fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62563/62563fig4v2.jpg" /> 
Figure 4: Magnetic susceptibility, or magnetization normalized to applied magnetic field, as a function of temperature for both CVT grown and flux grown UTe2.&#160;The samples show similar behavior, including a characteristic kink at approximately 10 K. A magnetic field H = 1000 Oe is applied parallel to the crystallographic a-axis. <a href="https://www.jove.com/files/ftp_upload/62563/62563fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride at JoVE.com

Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

Here, we present a protocol to synthesize two types of UTe2 crystals: those exhibiting robust superconductivity, via chemical vapor transport synthesis, and those lacking superconductivity, via molten metal flux synthesis.

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic ...

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2.7K Views.  University of Maryland. We demonstreren methoden om betrouwbaar enkele kristallen van uraniumdelluride te synthetiseren die beide supergeleiders niet hebben, wat cruciaal is voor het bestuderen van exotische spin-triplet supergeleiding. Volgens dit recept voor damptransport zullen we op betrouwbare wijze uraniumdelluridemonsters opleveren die bulksupergeleiding vertonen. Dit wordt niet bereikt met andere methoden.Deze methode beïnvloedt onderzoek naar spin-triplet en topologische supergeleiding, evenals geco...

Video: Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma ...

Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) coupled with synchrotron X-radiation. A cube-shaped sample assembly is prepared and compressed, at room temperature, by a set of four X-ray transparent sintered diamond anvils and two tungsten carbide anvils, in the lateral and the vertical planes, respectively. All six anvils are housed within a 250-ton hydraulic press and driven inward simultaneously by two wedged guide blocks. A horizontal energy dispersive X-ray beam is projected through and diffracted by the sample assembly. The beam is commonly in the mode of either white or monochromatic X-ray. In the case of white X-ray, the diffracted X-rays are detected by a solid-state detector array that collects the resulting energy dispersive diffraction pattern. In the case of monochromatic X-ray, the diffracted pattern is recorded using a two-dimensional (2-D) detector, such as an imaging plate or a charge-coupled device (CCD) detector. The 2-D diffraction patterns are analyzed to derive lattice spacings. The elastic strains of the sample are derived from the atomic lattice spacing within grains. The stress is then calculated using the predetermined elastic modulus and the elastic strain. Furthermore, the stress distribution in two-dimensions allow for understanding how stress is distributed in different orientations. In addition, a scintillator in the X-ray path yields a visible light image of the sample environment, which allows for the precise measurement of sample length changes during the experiment, yielding a direct measurement of volume strain on the sample. This type of experiment can quantify the stress distribution within geomaterials, which can ultimately shed light on the mechanism responsible for compaction. Such knowledge has the potential to significantly improve our understanding of key processes in rock mechanics, geotechnical engineering, mineral physics, and material science applications where compactive processes are important.

We report detailed procedures for compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus coupled with synchrotron X-radiation. Such experiments allow quantification of the stress distribution within samples, that ultimately sheds light on compaction processes in geomaterials.

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) ...

Environment

Spark Plasma Sintering Apparatus Used for the Formation of Strontium Titanate Bicrystals

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with one twist grain boundary. This apparatus utilizes high uniaxial pressure and a pulsed direct current for rapid consolidation of material. Diffusion bonding of strontium titanate bicrystals without fracture, in a spark plasma sintering apparatus, is possible at high pressures due to the unusual temperature dependent plasticity behavior of strontium titanate. We demonstrate a method for the successful formation of bicrystals at accelerated time scales and lower temperatures in a spark plasma sintering apparatus compared to bicrystals formed by conventional diffusion bonding parameters. Bond quality was verified by scanning electron microscopy. A clean and atomically abrupt interface containing no secondary phases was observed using transmission electron microscopy techniques. Local changes in bonding across the boundary was characterized by simultaneous scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy.

A viable technique for the formation of strontium titanate bicrystals at high pressure and fast heating rate via the spark plasma sintering apparatus is developed.

A spark plasma sintering apparatus was used as a novel method for diffusion bonding of two single crystals of strontium titanate to form bicrystals with ...

Engineering

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bis(thiourea) Cadmium Chloride Crystals and the Subsequent CdS Obtention

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of 367 nm using the chemical bath deposition technique are studied comparatively. Two experiments are performed to make a comparison: one without UV light and the other with the aid of UV light. Both experiments are performed under equal conditions, at a temperature of 343 K and with a pH of 3.2. The precursors used are cadmium chloride (CdCl2) and thiourea [CS(NH2)2], which are dissolved in 50 mL of deionized water with an acidic pH. In this experiment, the interaction of electromagnetic radiation is sought at the moment the chemical reaction is carried out. The results demonstrate the existence of an interaction between the crystals and the UV light; the UV light assistance causes crystal growths in an acicular shape. Also, the final product obtained is cadmium sulfide and shows no evident difference when synthesized with or without the use of UV light.

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention

This article presents a protocol for the synthesis of bis(thiourea) cadmium chloride crystals by chemical bath deposition. Two experiments are described: one aided by ultraviolet light compared to one without ultraviolet light.

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of ...

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

We describe a method to produce U2O5 films in situ using the Labstation, a modular machine developed at JRC Karlsruhe. The Labstation, an essential part of the Properties of Actinides under Extreme Conditions laboratory (PAMEC), allows the preparation of films and studies of sample surfaces using surface analytical techniques such as X-ray and ultra-violet photoemission spectroscopy (XPS and UPS, respectively). All studies are made in situ, and the films, transferred under ultra-high vacuum from their preparation to an analyses chamber, are never in contact with the atmosphere. Initially, a film of UO2 is prepared by direct current (DC) sputter deposition on a gold (Au) foil then oxidized by atomic oxygen to produce a UO3 film. This latter is then reduced with atomic hydrogen to U2O5. Analyses are performed after each step involving oxidation and reduction, using high-resolution photoelectron spectroscopy to examine the oxidation state of uranium. Indeed, the oxidation and reduction times and corresponding temperature of the substrate during this process have severe effects on the resulting oxidation state of the uranium. Stopping the reduction of UO3 to U2O5 with single U(V) is quite challenging; first, uranium-oxygen systems exist in numerous intermediate phases. Second, differentiation of the oxidation states of uranium is mainly based on satellite peaks, whose intensity peaks are weak. Also, experimenters should be aware that X-ray spectroscopy (XPS) is a technique with an atomic sensitivity of 1% to 5%. Thus, it is important to obtain a complete picture of the uranium oxidation state with the entire spectra obtained on U4f, O1s, and the valence band (VB). Programs used in the Labstation include a linear transfer program developed by an outside company (see Table of Materials) as well as data acquisition and sputter source programs, both developed in-house.

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

This protocol presents the preparation of U2O5 thin films obtained in situ under ultra-high vacuum. The process involves oxidation and reduction of UO2 films with atomic oxygen and atomic hydrogen, respectively.

We describe a method to produce U2O5 films in situ using the Labstation, a modular machine developed at JRC Karlsruhe. The Labstation, an essential part ...

Visualizing Uniaxial-strain Manipulation of Antiferromagnetic Domains in Fe1+YTe Using a Spin-polarized Scanning Tunneling Microscope

The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements toward the development of new experimental techniques and methodologies. Here we use a novel home-built uniaxial-strain device integrated into our variable temperature scanning tunneling microscope that enables us to controllably manipulate in-plane uniaxial strain in samples and probe their electronic response at the atomic scale. Using scanning tunneling microscopy (STM) with spin-polarization techniques, we visualize antiferromagnetic (AFM) domains and their atomic structure in Fe1+yTe samples, the parent compound of iron-based superconductors, and demonstrate how these domains respond to applied uniaxial strain. We observe the bidirectional AFM domains in the unstrained sample, with an average domain size of ~50-150 nm, to transition into a single unidirectional domain under applied uniaxial strain. The findings presented here open a new direction to utilize a valuable tuning parameter in STM, as well as other spectroscopic techniques, both for tuning the electronic properties as for inducing symmetry breaking in quantum material systems.

Visualizing Uniaxial-strain Manipulation of Antiferromagnetic Domains in Fe1+YTe Using a Spin-polarized Scanning Tunneling Microscope

Using uniaxial strain combined with spin-polarized scanning tunneling microscopy, we visualize and manipulate the antiferromagnetic domain structure of Fe1+yTe, the parent compound of iron-based superconductors.

The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements toward the development of new experimental ...

An Externally-Heated Diamond Anvil Cell for Synthesis and Single-Crystal Elasticity Determination of Ice-VII at High Pressure-Temperature Conditions

The externally-heated diamond anvil cell (EHDAC) can be used to generate simultaneously high-pressure and high-temperature conditions found in Earth&#8217;s and planetary interiors. Here we describe the design and fabrication of the EHDAC assemblies and accessories, including ring resistive heaters, thermal and electrical insulating layers, thermocouple placement, as well as the experimental protocol for preparing the EHDAC using these parts. The EHDAC can be routinely used to generate megabar pressures and up to 900 K temperatures in open air, and potentially higher temperatures up to ~1200 K with a protective atmosphere (i.e., Ar mixed with 1% H2). Compared with a laser-heating method for reaching temperatures typically &#62;1100 K, external heating can be easily implemented and provide a more stable temperature at &#8804;900 K and less temperature gradients to the sample. We showcased the application of the EHDAC for synthesis of single crystal ice-VII and studied its single-crystal elastic properties using synchrotron-based X-ray diffraction and Brillouin scattering at simultaneously high-pressure high-temperature conditions.

This work focuses on the standard protocol for preparing the externally-heated diamond anvil cell (EHDAC) for generating high-pressure and high-temperature (HPHT) conditions. The EHDAC is employed to investigate materials in Earth and planetary interiors under extreme conditions, which can be also used in solid state physics and chemistry studies.

The externally-heated diamond anvil cell (EHDAC) can be used to generate simultaneously high-pressure and high-temperature conditions found in ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...

Synthesis of High-ZT Thermoelectric Materials via Mechanochemical Methods

Demonstrating the Simplicity and In Situ Temperature Monitoring of the Mechanochemical Synthesis of Metal Chalcogenides Suitable for Thermoelectrics

Mechanochemical synthesis is an extremely useful strategy to reach thermoelectric materials due to its solvent-free one-step character, as the targeted thermoelectricity (TE) materials in a nanocrystalline format can be prepared by mere high-energy milling of elemental precursors. Nevertheless, the subsequent densification method (e.g., spark plasma sintering or hot pressing) is required afterward, similarly to other synthetic methodologies. In this study, the simplicity of mechanochemical synthesis is&#160;presented for two selected metal chalcogenides, namely copper sulfide (Cu1.8S, digenite) and tin selenide (SnSe, svetlanaite), which are known for high ZT values. These compounds can be prepared via a mechanically induced self-propagating reaction (MSR), which is a combustion-like process instantly yielding the products in a very short timeframe (within 1 min). The occurrence of MSR can be well-tracked by in situ temperature monitoring since an abrupt temperature increase occurs at the moment of MSR. We have developed a device which is capable of monitoring the temperature inside the milling jar every 80 ms during planetary ball milling, and it is therefore possible to very precisely track the moment of MSR ignition. The developed device presents an improvement in the monitoring capabilities in comparison with commercially available analogs. This contribution aims to provide a visual insight into all steps, with simple high-energy ball milling of elements to reach TE materials and in situ temperature monitoring being the central points.

Here, we present a protocol to synthesize two metal chalcogenides (Cu1.8S and SnSe) suitable for thermoelectrics via an ultrafast (second-range), solvent-free, and one-step mechanochemical synthesis using elemental precursors. Simultaneously, we demonstrate the monitoring of the temperature in the jar during planetary ball milling in situ by the newly developed device.

Mechanochemical synthesis is an extremely useful strategy to reach thermoelectric materials due to its solvent-free one-step character, as the targeted ...

Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

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