High Pressure Single Crystal Diffraction at PX^2

In this report we describe detailed procedures for carrying out single crystal X-ray diffraction experiments with a diamond anvil cell (DAC) at the ...

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 ...

University of Hawai’i at Manoa

University of Hawai'i at Mānoa

University of Chicago

Patterning mammalian cells for modeling three types of naturally occurring cell-cell interactions.

Earth's inner core is known to consist of crystalline iron alloyed with a small amount of nickel and lighter elements, but the shear wave (S wave) travels through the inner core at about half the speed expected for most iron-rich alloys under relevant pressures. The anomalously low S-wave velocity (vS) has been attributed to the presence of liquid, hence questioning the solidity of the inner core. Here we report new experimental data up to core pressures on iron carbide Fe7C3, a candidate component of the inner core, showing that its sound velocities dropped significantly near the end of a pressure-induced spin-pairing transition, which took place gradually between 10 GPa and 53 GPa. Following the transition, the sound velocities increased with density at an exceptionally low rate. Extrapolating the data to the inner core pressure and accounting for the temperature effect, we found that low-spin Fe7C3 can reproduce the observed vS of the inner core, thus eliminating the need to invoke partial melting or a postulated large temperature effect. The model of a carbon-rich inner core may be consistent with existing constraints on the Earth's carbon budget and would imply that as much as two thirds of the planet's carbon is hidden in its center sphere.

Hidden carbon in Earth's inner core revealed by shear softening in dense Fe7C3.

We have developed a multi-wavelength Fast Temperature Readout (FasTeR) spectrometer to capture a sample's transient temperature fluctuations, and reduce uncertainties in melting temperature determination. Without sacrificing accuracy, FasTeR features a fast readout rate (about 100 Hz), high sensitivity, large dynamic range, and a well-constrained focus. Complimenting a charge-coupled device spectrometer, FasTeR consists of an array of photomultiplier tubes and optical dichroic filters. The temperatures determined by FasTeR outside of the vicinity of melting are, generally, in good agreement with results from the charge-coupled device spectrometer. Near melting, FasTeR is capable of capturing transient temperature fluctuations, at least on the order of 300 K/s. A software tool, SIMFaster, is described and has been developed to simulate FasTeR and assess design configurations. FasTeR is especially suitable for temperature determinations that utilize ultra-fast techniques under extreme conditions. Working in parallel with the laser-heated diamond-anvil cell, synchrotron Mössbauer spectroscopy, and X-ray diffraction, we have applied the FasTeR spectrometer to measure the melting temperature of (57)Fe0.9Ni0.1 at high pressure.

Fast temperature spectrometer for samples under extreme conditions.

The organic-inorganic hybrid lead trihalide perovskites have been emerging as the most attractive photovoltaic materials. As regulated by Shockley-Queisser theory, a formidable materials science challenge for improvement to the next level requires further band-gap narrowing for broader absorption in solar spectrum, while retaining or even synergistically prolonging the carrier lifetime, a critical factor responsible for attaining the near-band-gap photovoltage. Herein, by applying controllable hydrostatic pressure, we have achieved unprecedented simultaneous enhancement in both band-gap narrowing and carrier-lifetime prolongation (up to 70% to ∼100% increase) under mild pressures at ∼0.3 GPa. The pressure-induced modulation on pure hybrid perovskites without introducing any adverse chemical or thermal effect clearly demonstrates the importance of band edges on the photon-electron interaction and maps a pioneering route toward a further increase in their photovoltaic performance.

Simultaneous band-gap narrowing and carrier-lifetime prolongation of organic-inorganic trihalide perovskites.

The structural phase transition of synthetic ZnFeO nanoparticles (ZFO NPs) is investigated as a function of pressure up to 40.6 GPa at room temperature for the first time, and its associated intriguing electrical transport properties are resolved from in situ impedance spectra and magnetoresistivity measurements. Significant anomalies are observed in the properties of the grain boundary resistance ( R), the relaxation frequency ( f), and the relative permittivity (ε) in the ZFO NPs under the pressures around 17.5-21.5 GPa. These anomalies are believed to be correlated with a cubic-to-orthorhombic phase transition of ZnFeO at the pressures between 21.9 and 25.7 GPa, which is found to be partially reversible. The pressure-tuned dielectric properties are measured for the cubic and the orthorhombic phases of ZFO, respectively. Remarkably, R decreases up to 6 orders of magnitude as a function of pressure in the cubic phase. The dielectric polarization is obviously strengthened with increased f and decreased ε with pressure in the orthorhombic phase. Furthermore, it is confirmed that the external pressure effectively improves the electrochemical stability of the sample based on the cycled measurements of the impedance spectra at various pressures. The changes in the complex permittivity (ε', ε″) and the dielectric loss tangent (tan δ) with frequency reveal the irreversible increase in the dielectric loss accompanied by phase transition. The MR measurements indicate that ZFO NPs are superparamagnetic under high pressure of up to 40 GPa. The transmission electron microscopy images reflect the decrease in the grain boundary number and some local amorphization of grains after compression, which provides good explanations for the changes in the electrical transport properties as a function of pressure. Herein, the structural and electrical properties of ZnFeO NPs generated are preserved by quenching the high-pressure phase to ambient conditions, thus providing great choices of ferrites materials for a variety of applications.

Correlation between Structural Changes and Electrical Transport Properties of Spinel ZnFeO Nanoparticles under High Pressure.

Solid-solid reaction, particularly in the Fe-O binary system, has been extensively studied in the past decades because of its various applications in chemistry and materials and earth sciences. The recently synthesized pyrite-FeO at high pressure suggested a novel oxygen-rich stoichiometry that extends the achievable O-Fe ratio in iron oxides by 33%. Although FeO was synthesized from FeO and O, the underlying solid reaction mechanism remains unclear. Herein, combining in situ X-ray diffraction experiments and first-principles calculations, we identified that two competing phase transitions starting from FeO: (1) without O, perovskite-FeO transits to the post-perovskite structure above 50 GPa; (2) if free oxygen is present, O diffuses into the perovskite-type lattice of FeO leading to the pyrite-type FeO phase. We found the O-O bonds in FeO are formed by the insertion of oxygen into the Pv lattice via the external stress and such O-O bonding is only kinetically stable under high pressure. This may provide a general mechanism of adding extra oxygen to previous known O saturated oxides to produce unconventional stoichiometries. Our results also shed light on how O is enriched in mantle minerals under pressure.

Dongzhou Zhang

Hawai’i Institute of Geophysics and Planetology

University of Hawai’i at Manoa

High Pressure Single Crystal Diffraction at PX^2

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

Dongzhou Zhang

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University of Hawai’i at Manoa

High Pressure Single Crystal Diffraction at PX^2

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

Hawai’i Institute of Geophysics and Planetology