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Transition metal carbides find widespread use throughout industry due to their high strength and resilience under extreme conditions. However, they remain largely limited to compounds formed from the early d‐block elements, since the mid‐to‐late transition metals do not form thermodynamically stable carbides. We report here the high‐pressure bulk synthesis of large single crystals of a novel metastable manganese carbide compound, MnCx (P63/mmc), which adopts the anti‐NiAs‐type structure with significant substoichiometry at the carbon sites. We demonstrate how synthesis pressure modulates the carbon loading, with ~40 % occupancy being achieved at 9.9 GPa. [ABSTRACT FROM AUTHOR]

Seismic observations show the Earth's inner core has significant and unexplained variation in seismic attenuation with position, depth and direction. Interpreting these observations is difficult without knowledge of the visco‐ or anelastic dissipation processes active in iron under inner core conditions. Here, a previously unconsidered attenuation mechanism is observed in zinc, a low pressure analog of hcp‐iron, during small strain sinusoidal deformation experiments. The experiments were performed in a deformation‐DIA combined with X‐radiography, at seismic frequencies (∼0.003–0.1 Hz), high pressure and temperatures up to ∼80% of melting temperature. Significant dissipation (0.077 ≤ Q−1(ω) ≤ 0.488) is observed along with frequency dependent softening of zinc's Young's modulus and an extremely small activation energy for creep (⩽7 kJ mol−1). In addition, during sinusoidal deformation the original microstructure is replaced by one with a reduced dislocation density and small, uniform, grain size. This combination of behavior collectively reflects a mode of deformation called "internal stress superplasticity"; this deformation mechanism is unique to anisotropic materials and activated by cyclic loading generating large internal stresses. Here we observe a new form of internal stress superplasticity, which we name as "elastic strain mismatch superplasticity." In it the large stresses are caused by the compressional anisotropy. If this mechanism is also active in hcp‐iron and the Earth's inner‐core it will be a contributor to inner‐core observed seismic attenuation and constrain the maximum inner‐core grain‐size to ≲10 km. Plain Language Summary: The Earth's inner‐core is the most remote and inaccessible part of our planet. Knowledge of the inner‐core's structure comes from interpretation of the information held in seismic waves that have passed through the inner‐core. These waves show measurable variation in wave speed and damping with depth. To investigate the wave damping in the inner‐core we performed experiments that mimicked the passage of seismic waves through zinc. Zinc was used as a low‐pressure analog because it has the same crystallographic structure as the iron in the inner‐core. In these experiments, we observed new behavior in the zinc samples that can only be explained by the behavior of different directions within the zinc crystal lattice. These we named "elastic strain mismatch superplasticity" and if the same phenomena occurs in the Earth's inner‐core it could explain the seismic observations. Key Points: Zinc, a low pressure analog for hcp‐iron, deforms by internal stress superplasticity during small amplitude sinusoidal‐strain deformationInternal stress superplasticity due to mechanical oscillations has not been previously reportedInternal stress superplasticity is another attenuation mechanism that could be active in the Earth's inner‐core [ABSTRACT FROM AUTHOR]

Compressional (P) and shear (S) wave velocities across the olivine-spinel transformation in [Fe.sub.2]Si[O.sub.4] were investigated in situ using combined synchrotron X-ray diffraction, X-ray imaging, and ultrasonic interferometry up to 5.5 GPa along the 1173 K isotherm. The onset of the spinel to olivine transformation at 4.5 GPa and olivine to spinel transition for [Fe.sub.2]Si[O.sub.4] at 4.8 GPa was concurrently observed from X-ray diffraction, the amplitude of the ultrasonic signals, the calculated velocities, and the ratio of P and S wave velocities ([v.sub.P]/[v.sub.S]). No velocity softening was observed prior to the fayalite to spinel transition. The velocity contrasts across the [Fe.sub.2]Si[O.sub.4] spinel to fayalite phase transition are derived directly from the measured velocities, which are 13 and 12% for P and S waves, respectively, together with a density contrast of 9.4%. A comparison with literature data indicates that the changes in compressional-wave velocity and density across the olivine-spinel transformation in [Fe.sub.2]Si[O.sub.4] are comparable to those with different iron concentrations in the [(Mg,Fe).sub.2]Si[O.sub.4] solid solution, whereas the shear wave velocity contrast decreases slightly with increasing iron concentration. Keywords: Olivine-spinel, phase transformation, [Fe.sub.2]Si[O.sub.4], velocity contrasts, ultrasonic measurements, iron concentration DOI: 10.2138/am.2010.3369

The elastic properties of [epsilon]-FeSi were investigated at high temperature and pressure using a combination of ultrasonic interferometry and synchrotron radiation up to 8 GPa and 1273 K. The unit-cell volumes and sound velocity data were fit to third-order finite-strain equations with adiabatic temperature conversions to maintain a thermodynamically internally consistent data set. The adiabatic zero-pressure bulk and shear moduli and their first pressure and temperature derivatives were obtained from this fitting: [K.sub.SO] = 168.9(7) GPa, [G.sub.0] = 116.5(3) GPa, [K.sup.'.sub.SO] = 6.6(2), [G.sup.'.sub.0] = 2.9(1), [([delta][K.sub.SO][delta]T)).sub.P] = -0.023(1) GPa/K, [([delta][G.sub.0]/[delta]T).sub.P] = -0.030(1) GPa/K. This study presents the first complete thermodynamically consistent set of elastic moduli and their temperature and pressure derivatives. Keywords: Ultrasonic interferometry, equation of state, iron silicide, elastic properties, high pressure, high temperature

Experiments were conducted to determine whether the presence of graphite is required to produce the Fe-Ti-P-enrichment, silica-depletion trend seen in ferrobasalts and ferrodiorites/jotunites. A nominally anhydrous Snake River Plain olivine tholeiite was crystallized at 9.3 kbar in Fe-Pt capsules; the composition of the Fe-Pt alloy was empirically chosen such that the charge neither lost nor gained iron. The results of these experiments and those of previous experiments conducted in graphite are strikingly similar: in both cases the residual liquids were depleted in silica and enriched in Fe, Ti, and P. We conclude that the presence of carbon is not essential for producing this distinctive trend. Keywords: Experimental petrology, tholeiite, crystal-liquid differentiation, phase equilibria

Experiments have been conducted to measure compressional (VP) and shear wave (VS) velocities as well as unit-cell volumes (densities) of molybdenum to 12.0 GPa at room temperature using ultrasonic interferometry in conjunction with synchrotron x-radiation. Both VP and VS as well as the adiabatic bulk (KS) and shear (G) moduli exhibit monotonic increase with increasing pressure. A finite strain equation of state analysis of the directly measured velocities and densities yields KS0=260.7(5) GPa, G0=125.1(2) GPa, KS0′=4.7(1), and G0′=1.5(1) for the elastic bulk and shear moduli and their pressure derivatives at ambient conditions. Complimentary to the experimental data, VP and VS as well as the elastic bulk and shear moduli were also computed using density functional theory (DFT) at pressures comparable to the current experiment. Comparing with experimental results, the velocities and elastic moduli from DFT calculations exhibit close agreement with the current experimental data both in their values as well as in their pressure dependence. [ABSTRACT FROM AUTHOR]

The ultrasonic interferometry technique is employed to determine the different velocities, as well as the elasticity of molybdenum to 12.0 GPa at room temperature. An increase in the pressure exhibited on the compound is shown to lead to a monotonic increase in its velocities and the adiabatic bulk modulus.

The pressure-volume-temperature ( P- V- T) relation of CaIrO post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus $$ K_{T0} $$ at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative $$ K_{T0}^{\prime } $$ = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO ppv are: temperature derivative of bulk modulus $$ (\partial K_{T} /\partial T)_{P} $$ = −0.038 ± 0.011 GPa K, $$ \alpha K_{T} $$ = 0.0039 ± 0.0001 GPa K, $$ \left( {\partial K_{T} /\partial T} \right)_{V} $$ = −0.012 ± 0.002 GPa K, and $$ \left( {\partial^{2} P/\partial T^{2} } \right)_{V} $$ = 1.9 ± 0.3 × 10 GPa K. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter $$ \gamma_{0} $$ = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K = 5406.0/ V(molar) + 5.9 GPa. [ABSTRACT FROM AUTHOR]

Transition metal carbides find widespread use throughout industry due to their high strength and resilience under extreme conditions. However, they remain largely limited to compounds formed from the early d‐block elements, since the mid‐to‐late transition metals do not form thermodynamically stable carbides. We report here the high‐pressure bulk synthesis of large single crystals of a novel metastable manganese carbide compound, MnCx (P63/mmc), which adopts the anti‐NiAs‐type structure with significant substoichiometry at the carbon sites. We demonstrate how synthesis pressure modulates the carbon loading, with ~40 % occupancy being achieved at 9.9 GPa. [ABSTRACT FROM AUTHOR]

Compressional (P) and shear (S) wave velocities across the olivine-spinel transformation in Fe2SiO4 were investigated in situ using combined synchrotron X-ray diffraction, X-ray imaging, and ultrasonic interferometry up to 5.5 GPa along the 1173 K isotherm. The onset of the spinel to olivine transformation at 4.5 GPa and olivine to spinel transition for Fe2SiO4 at 4.8 GPa was concurrently observed from X-ray diffraction, the amplitude of the ultrasonic signals, the calculated velocities, and the ratio of P and S wave velocities (vP/vS). No velocity softening was observed prior to the fayalite to spinel transition. The velocity contrasts across the Fe2SiO4 spinel to fayalite phase transition are derived directly from the measured velocities, which are 13 and 12% for P and S waves, respectively, together with a density contrast of 9.4%. A comparison with literature data indicates that the changes in compressional-wave velocity and density across the olivine-spinel transformation in Fe2SiO4 are comparable to those with different iron concentrations in the (Mg,Fe)2SiO4 solid solution, whereas the shear wave velocity contrast decreases slightly with increasing iron concentration. [ABSTRACT FROM AUTHOR]

Compressional (P) and shear (S) wave velocities across the olivine-spinel transformation in Fe2SiO4 were investigated in situ using combined synchrotron X-ray diffraction, X-ray imaging, and ultrasonic interferometry up to 5.5 GPa along the 1173 K isotherm. The onset of the spinel to olivine transformation at 4.5 GPa and olivine to spinel transition for Fe2SiO4 at 4.8 GPa was concurrently observed from X-ray diffraction, the amplitude of the ultrasonic signals, the calculated velocities, and the ratio of P and S wave velocities (vP/vS). No velocity softening was observed prior to the fayalite to spinel transition. The velocity contrasts across the Fe2SiO4 spinel to fayalite phase transition are derived directly from the measured velocities, which are 13 and 12% for P and S waves, respectively, together with a density contrast of 9.4%. A comparison with literature data indicates that the changes in compressional-wave velocity and density across the olivine-spinel transformation in Fe2SiO4 are comparable to those with different iron concentrations in the (Mg,Fe)2SiO4 solid solution, whereas the shear wave velocity contrast decreases slightly with increasing iron concentration. [ABSTRACT FROM AUTHOR]

Transition metal carbides find widespread use throughout industry due to their high strength and resilience under extreme conditions. However, they remain largely limited to compounds formed from the early d-block elements, since the mid-to-late transition metals do not form thermodynamically stable carbides. We report here the high-pressure bulk synthesis of large single crystals of a novel metastable manganese carbide compound, MnC x (P6 3 /mmc), which adopts the anti-NiAs-type structure with significant substoichiometry at the carbon sites. We demonstrate how synthesis pressure modulates the carbon loading, with ~40 % occupancy being achieved at 9.9 GPa., (© 2024 Wiley-VCH GmbH.)