Search

The negative thermal-expansion material zirconium tungstate, when subjected to a moderate pressure of 2 GPa, turns amorphous irreversibly; the amorphous state being $\ensuremath{\sim}26\mathrm{%}$ more dense than the crystalline phase $\ensuremath{\alpha}\text{-Zr}{({\text{WO}}_{4})}_{2}$. Structure of pressure-amorphized $\text{Zr}{({\text{WO}}_{4})}_{2}$ is investigated using synchrotron x-ray diffraction. Structure factors $S(q)$ of samples recovered from different pressures are obtained. The first peak in $S(q)$ for 10.5 GPa-treated sample is found to occur at a slightly larger $q$ than that recovered from 5.5 GPa, suggesting that the amorphous samples recovered from higher pressure could be more dense. The pair-correlation functions $g(r)$, obtained by Fourier transforming $S(q)$, suggests that the further densification of amorphous phase occurs via contraction of second and third neighbor shells representing O-O and W-W and W-Zr distances rather than first neighbor shell. In contrast to earlier speculations, the present results do not show evidence for an increase in the coordination number and consequent existence of distinct amorphous phases in samples recovered from pressures up to 10.5 GPa.

[1] The behavior of Xe-Fe system was investigated under ultra-high pressures by in situ X-ray diffraction measurements using a laser-heated diamond anvil cell. Although Xe-Fe interaction have been regarded as one of the most probable explanations for the missing Xe problem, no compounds and no detectable amounts of dissolution of xenon into crystalline hcp iron occur even above the metallization pressure of xenon up to 155 GPa and 3000 K. Furthermore, the c/a ratio of hcp xenon and iron vary in opposite ways with increasing pressure, indicating that the nature of these two metals deviates more at high pressures. These results and the fact that incorporation of nickel and light elements into iron tends to stabilize structures other than the hcp structure imply that the retention of xenon in the Earth's core is very unlikely by a solid-solution mechanism, and some other mechanism needs to be found to explain the missing xenon problem.

The pressure dependence of the Brillouin scattering frequency shift of MnF 2 shows a discrete jump near the phase transition pressure of 1.49 GPa with increasing pressure. The phase transition was confirmed to be a first-order one from the hysteresis on the pressure dependence of the sound velocity, in addition to the discrete jump in sound velocity. The softening of the acoustic mode coupled with the soft B 1 g optical mode was not observed, contrary to the recent molecular dynamical simulation of SiO 2 . The phase transition mechanism seems to be somewhat different from the rutile-CaCl 2 type.

The bulk modulus of MgSiO3 tetragonal garnet was measured using a diamond anvil-type high-pressure apparatus combined with synchrotron radiation. An imaging plate X-ray detector was used to get high resolution diffraction data and the whole-powder-pattern decomposition method was employed to analyze the tetragonal unit cell which was only slightly distorted from cubic symmetry. The isothermal bulk modulus (K0) of the garnet-structured MgSiO3 was determined to be 161 GPa when ( d K d P ) 0 was assumed to be 4. Combining this result with previous results, the compositional dependence of the bulk modulus of majorite in a pyrope-enstatite join is expressed as K 0 (GPa) =(171.8±3.5)−(0.11±0.5)X En where XEn is the mole fraction of the enstatite composition in majorite.

High-pressure in situ x-ray diffraction was carried out to clarify the nature of the pressure-induced phase transformation in graphite at room temperature. The combined use of a Drickamer-type high-pressure apparatus with sintered diamond as an anvil material and very intense x rays from synchrotron radiation made it possible to obtain high-quality x-ray-diffraction data, as well as information on the orientation relation, for this phase transformation. It was found that the transition starts at 14 GPa at room temperature, although this onset pressure is sensitive to the nature of the sample and of the applied pressure. X-ray-diffraction profiles obtained on the high-pressure phase are well explained by the hexagonal diamond structure, but the observed c/a ratio is slightly larger than that of ideal packing. The observed orientation relation satisfies the previously proposed martensitic transition mechanism from graphite to hexagonal diamond. But this hexagonal diamond formed at room temperature is unquenchable upon the release of pressure, and how it differs from the quenched phase formed under high pressure and temperature remains to be clarified.

The absorption spectra of [Ni(dmg)2], [Ni(niox)2], [Ni(dpg)2], and [Ni(bqd)2] were studied at various pressures. Two characteristic absorption bands, the metal-to-ligand charge-transfer (M–L) and the 3d–4p bands, were observed in the visible region for these complexes. The interesting spectral features observed under high pressures were: (1) The excitations shift remarkably to lower energies with increasing pressure. (2) The rates of the peak shifts for the d–p and M–L bands increase in the order [Ni(niox)2] < [Ni(dmg)2] < [Ni(dpg)2]. (3) The peak shifts of the M–L bands are much smaller than those of the d–p bands. (4) The absorption intensity of the M–L band of [Ni(niox)2] decreases rapidly above 10 GPa, and the band is hardly observed at around 14 GPa. (5) A new absorption band in [Ni(dpg)2] exists above about 3 GPa. The electrical resistivity of [Ni(dmg)2], [Ni(niox)2], and [Ni(dpg)2] has been studied under high pressures. These complexes are insulators with a resistivity of 1015 Ω cm at atmospheric p...

The behavior of iron hydride was studied by in situ X-ray observations at 6GPa up to 700°C. When the iron-hydrogen system was heated, the dissolution of hydrogen into iron occurred, and bcc iron changed into iron hydride with a dhcp structure passing through a hcp structure, and then transformed into an fcc structure. The unit cell volumes per iron atom of these phases are much larger than those of bcc and hcp iron, which suggests that the iron hydride is formed. It was also found that the volume of the dhcp phase decreases with increasing temperature above 250°C, which indicates that the hydrogen concentration decreases at high temperatures.

The systems (Fe, Ni)-silicate-water, (Fe, Co)-silicate-water and (Fe, Ni)-silicate-water-sulfur were investigated at around 5 GPa and 1000–1500°C by using a tetrahedral-anvil and cubic-anvil high-pressure apparatus. The quenched samples showed the coexistence of olivine, pyroxene and metal. The distribution behavior of Fe, Ni and Co between metal-olivine and metal-pyroxene was measured in these quenched samples. The observed values of apparent partition coefficients, K ′(FeNi) and K ′(FeCo), were approximately 40–100 and 10–30, respectively. These values are 10–100 times larger than the estimated value for the Earth's core and mantle, and would indicate that the Earth could not be in equilibrium as a total system. To explain the observed transition metal abundance in the Earth, it is necessary to consider the accretion process and the core formation processes in the partially molten layer of the proto-Earth.

The absorption spectra of Pd(niox)2, Pd(dmg)2 and Pd(dpg)2 have been studied at high pressures. The absorption bands based on the 4dz2-5pz transition shifted rapidly to longer wavelengths with increasing pressure. The mean rates of the red shift with pressure were ca. -1170cm-1/GPa for Pd(niox)2, ca. -1300cm-1/GPa for Pd(dmg)2 and ca. -1990cm-1/GPa for Pd(dpg)2. A new pressure-induced absorption band at around 410nm was observed for Pd(niox)2 above 10GPa. The electronic states of the palladium complexes are discussed. The colors of the complexes in the diamond-anvil pressure cell were observed visually at various pressures. The colors of the complexes turn from yellow to orange and then to successive colors in the visible spectrum with increasing pressure. These materials can be utilized as a pressure indicator over the wide pressure range.

A newly developed diamond composite (Advanced Diamond Composite, ADC) was tested as the anvil material for a double-stage multianvil (MA6-8) apparatus. Pressures over 30GPa at room temperature were produced at relatively small press loads without any significant damages on the ADC anvils. The ADC anvil was found to be more transparent to X-ray beams of a wide range of energy as compared with a competitive sintered polycrystalline diamond (SYNDIE), and is accordingly suitable for an X-ray window under pressure. Electrical resistivity of ADC, however, is higher by about one order of magnitude than that of SYNDIE, which would restrict its use as a lead for electric power supply to the furnace. A hybrid anvil system with four ADC anvils plus four tungsten carbide anvils, the latter being used as the electric leads, was introduced for high temperature runs. This system has enabled to generate temperatures to 1500°C at pressures of 25-33GPa and to synthesize high-pressure phases relevant to the lower mantle mineralogy.

Recent high pressure and high temperature in situ X-ray experiments using synchrotron radiation are reviewed. Among them are the behavior of Fe-H system, the conversion of graphite into hexagonal diamond, and an in situ observation of the formation of MgSiO3 perovskite from enstatite. The latter two studies were made by the newly developed Drick-amer-type high pressure apparatus using sintered diamond anvil, which is capable up to at least 30 GPa and 1500°C. Experiments up to 210 GPa were performed using diamond anvil apparatus combined with a very thin collimator system. A design of the apparatus to be constructed in the new synchrotron facility is discussed.

Ternary metal arsenides LaT 4 As 12 (T=Fe, Ru and Os) with a skutterudite-type structure have been prepared at high temperatures and high pressures. These arsenides showed the superconducting transition at around 10.3 K for LaRu 4 As 12 and 3.2 K for LaOs 4 As 12 . The T c s of both these arsenides are considerably higher than those of the corresponding phosphides. LaOs 4 As 12 is a new superconductor. On the other hand, LaFe 4 As 12 did not show the superconducting transition down to 2 K.

We report a novel superconducting (SC) and antiferromagnetic (AF) hybrid state in ${\mathrm{SrFe}}_{2}{\mathrm{As}}_{2}$ revealed by $^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) experiments on a single crystal under highly hydrostatic pressure up to 7 GPa. The NMR spectra at 5.4 GPa indicate simultaneous development of the SC and AF orders below 30 K. The nuclear spin-lattice relaxation rate in the SC domains shows a substantial residual density of states, suggesting proximity effects due to the spontaneous formation of a nanoscale SC-AF hybrid structure. This entangled behavior is a remarkable example of a self-organized heterogeneous structure in a clean system.

The hollandite chromium oxide K2Cr8O16 has been synthesized in both powder and single-crystal form under high pressure. Combining electrical resistivity, magnetic susceptibility, and x-ray diffraction, we found that K2Cr8O16 is a ferromagnetic metal (or half-metal) with T(C)=180 K and shows a transition to an insulator at 95 K without any apparent structural change but retaining ferromagnetism. K2Cr8O16 is quite unique in three aspects: It has a rare mixed valence of Cr3+ and Cr4+; it has a metal (or half-metal)-to-insulator transition in a ferromagnetic state; and the resulting low-temperature phase is a rare case of a ferromagnetic insulator. This discovery could open a new frontier on the relation of magnetism and conducting properties in strongly correlated electron systems.

The hollandite chromium oxide K2Cr8O16 has been synthesized in both powder and single-crystal form under high pressure. Combining electrical resistivity, magnetic susceptibility, and x-ray diffraction, we found that K2Cr8O16 is a ferromagnetic metal (or half-metal) with T(C)=180 K and shows a transition to an insulator at 95 K without any apparent structural change but retaining ferromagnetism. K2Cr8O16 is quite unique in three aspects: It has a rare mixed valence of Cr3+ and Cr4+; it has a metal (or half-metal)-to-insulator transition in a ferromagnetic state; and the resulting low-temperature phase is a rare case of a ferromagnetic insulator. This discovery could open a new frontier on the relation of magnetism and conducting properties in strongly correlated electron systems.

The electrical resistivities and absorption spectra of one-dimensional bis(1,2-dione dioximato)Pt(II) have been studied at high pressures. The resistivities of needle crystals of Pt(dmg)2 and Pt(bqd)2 were measured in detail under a quasi-hydrostatic pressure of up to 7 GPa. Pt(dmg)2 is an insulator with a resistivity of 1015 Ω cm, and Pt(bqd)2 is a semiconductor with 103 Ω cm at atmospheric pressure. A pressure-induced insulator (semiconductor)-to-metal transition was observed for both complexes. This transition arises from a crossing of the 5dz2 valence and 6pz conduction bands. When the pressure was further increasued, a metal-to-semiconductor transition took place at around the pressure that showed a resistivity minimum. A new pressure-induced absorption band was found in the visible region for the Pt complexes. The new band did not shift with pressure; the intensity of the band, however, increased with pressure over a narrow pressure region. The pressure-induced band may be due to intramolecular d–d ...

High-pressure and high-temperature stability of MgCO3 magnesite was investigated using a lever and spring type of diamond anvil cell up to 55GPa at about 1300°C. No phase transformation was observed in magnesite at the pressures investigated. Magnesite would be a dominant carbon-reservoir in the lower mantle. The volume of magnesite at 55GPa is 77% of that at the atmospheric pressure. The compressibility in the c-axis is 8% larger than that in the a-axis.

In situ X-ray observation under high pressure was carried out to investigate the phase transformation in graphite induced by room temperature compression. Several diffraction peaks of the high pressure phase were clearly observed and could be indexed as a hexagonal diamond structure. The diffraction profiles from two different directions support the orientation relationship of the martensitic transformation from graphite to hexagonal diamond previously proposed. This hexagonal diamond has a large bulk modulus comparable to the cubic diamond.

The origin of photoluminescence quenching due to the application of hydrostatic pressure on a-Si:H has been elucidated by the optically detected magnetic resonance (ODMR) measurements. Hydrostatic pressure of ∼ 5 GPa was applied on a sample by a wedge type cubic anvil apparatus, and after the release of pressure the ODMR measurement was carried out. As a result, it has been found that the quenching signal due to dangling bonds was increased by pressure. This result has also been confirmed by electron spin resonance (ESR) measurement. Photo-induced defect creation was examined for the sample treated by pressure. Further increase of dangling bond density has been observed. These results are discussed on the basis of a model that both of the photo-induced and pressure-induced defect creation are related to void and microvoid in the samples which contain Si-H bond cluster on their internal surface.

Combining infrared reflectivity, transport, susceptibility, and several diffraction techniques, we find compelling evidence that CaCrO3 is a rare case of a metallic and antiferromagnetic transition-metal oxide with a three-dimensional electronic structure. Local spin density approximation calculations correctly describe the metallic behavior as well as the anisotropic magnetic ordering pattern of C type: The high Cr valence state induces via sizable pd hybridization remarkably strong next-nearest-neighbor interactions stabilizing this ordering. The subtle balance of magnetic interactions gives rise to magnetoelastic coupling, explaining pronounced structural anomalies observed at the magnetic ordering transition.

Phase transformations of pure ${\mathrm{ZrO}}_{2}$ at high pressure up to 60 GPa were investigated by using x-ray diffraction and micro-Raman-scattering methods. The existence of phase transformation at about 13 GPa was reconfirmed by the spectral change of in situ Raman scattering. A new phase transformation at 35 GPa was observed from both of the experimental methods employed. A new high-pressure phase is stable up to 60 GPa and quenchable to ambient conditions. The measured x-ray diffraction pattern for this high-pressure phase was indexed on the basis of tetragonal symmetry. Eight Raman bands were observed for the quenched high-pressure phase. Candidate space groups that are consistent with the obtained experimental results were deduced. The most plausible space group is considered as one of ${\mathit{C}}_{4\mathit{h}}^{1}$, ${\mathit{C}}_{4\mathit{h}}^{4}$, ${\mathit{D}}_{4\mathit{h}}^{1}$, or ${\mathit{D}}_{4\mathit{h}}^{5}$ (P4/m, ${\mathrm{P}4}_{2}$/n, P4/mmm, or P4/mbm). The molar volume for the new high-pressure phase is smallest in the high-pressure phases so far reported for ${\mathrm{ZrO}}_{2}$. .AE

A cylindrical furnace with a homogeneous temperature distribution was designed for use in a cubic press by using the difference method. This method consists of three tubes and is applicable to the very small sample chamber of high‐pressure apparatus. The temperature distribution in the furnace thus designed was measured at high pressure and temperature using two methods: (1) by measuring the thermal expansion of NaCl contained in the sample chamber; and (2) by observing the area of molten Pb which was mixed with the NaCl. Both of these measurements were performed by high‐pressure and temperature in situ x‐ray techniques. It was confirmed from these experiments that the furnace has a homogeneous temperature distribution and the difference in temperature is less than 5 °C when the center is about 600 °C. The homogeneity in temperature is nearly constant, even when the thermal conductivity of the sample is decreased by two orders of magnitude.

ZnSiO3 clinopyroxene stable above 3 GPa transforms to ilmenite at 10–12 GPa, which further decomposes into ZnO (rock salt) plus stishovite at 20–30 GPa. The enthalpy of the clinopyroxene-ilmenite transition was measured by high-temperature solution calorimetry, giving ΔH0=51.71 ±3.18 kJ/mol at 298 K. The heat capacities of clinopyroxene and ilmenite were measured by differential scanning calorimetry at 343–733 and 343–633 K, respectively. The Cp of ilmenite is 3–5% smaller than that of clinopyroxene. The entropy of transition was calculated using the measured enthalpy and the free energy calculated from the phase equilibrium data. The enthalpy, entropy and volume changes of the pyroxene-ilmenite transition in ZnSiO3 are similar in magnitude to those in MgSiO3. The present thermochemical data are used to calculate the phase boundary of the ZnSiO3 clinopyroxene-ilmenite transition. The calculated boundary, $$P(Gpa) = 8.9( \pm 0.6) + 1.7(\bar + 0.5)$$ . 10−3, is more tightly constrained than those determined previously by high-pressure high-temperature experiments, and can be used as a pressure calibration at 10–12 GPa and 1000–2000 K. The disproportionation of ZnSiO3 ilmenite to ZnO (rock salt) plus stishovite is calculated to occur at about 25 GPa at 1000–2000 K.

Melting curve of methane was measured up to 4.8GPa and 260°C using a diamond anvil type high pressure-temperature apparatus. Pressure and temperature in the sample chamber were measured from the wavelength and the line width of the fluorescence line emitted from a ruby chip placed in the sample chamber. This melting curve provides important constraint on the evolution of the icy satellites.

We report on systematic study of superconducting characteristics and Pr crystalline-electric-field (CEF) levels of filled-skutterudite \pra ($T_{\rm c}$ = 2.33 K). The temperature dependences of the upper critical field $H_{\rm c2}$ and the Ginzburg-Landau (Maki) parameter $\kappa_2$ suggest an s-wave clean-limit superconductivity. The electronic specific heat coefficient $\gamma \sim 95$ mJ/K$^2$mol, being $\sim 1.5$ times larger than that for \lra, indicates $4f$-originating quasiparticle mass enhancement. Magnetic susceptibility $\chi(T)$ indicates that the CEF ground state is a $\Gamma_1$ singlet and a $\Gamma_4^{(1)}$ triplet first excited state lies at $\Delta_{\rm CEF}\sim 30$ K above. Systematic comparison among \pos, \prs, \pra and La-based reference compounds suggests that inelastic exchange- and aspherical-charge-scatterings of conduction electrons from CEF-split $4f$ levels play an essential role for the quasiparticle mass enhancement and the value of $T_{\rm c}$ in the Pr-based filled skutterudites., Comment: 4 pages, 6 figures

Compression curves and stability of melanophlogite, a natural mineral formed by $\mathrm{Si}{\mathrm{O}}_{2}$ clathrate, have been studied up to about $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ by using various pressure-transmitting media. We have studied both unheated and preheated samples to understand the role of guest gas molecules in clathrate. All the high-pressure experiments were made at room temperature using a diamond-anvil apparatus combined with synchrotron radiation. Unheated melanophlogite amorphized irreversibly without any structural transition at about $17\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, where the volume was decreased to about 70% of its original volume. Identical results were obtained in experiments using methane or an alcohol-water mixture as pressure-transmitting media or when direct compression was applied. Preheated melanophlogite, on the other hand, became much more compressible and amorphized only at around $3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ when the volume was decreased to 80%. The behavior changed completely when helium was used as the pressure-transmitting medium. The unheated sample was much less compressible but neither phase transition nor amorphization was observed up to about $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Preheated samples had the same compression curve up to about $17\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, where an isostructural transition occurred, accompanied by a 10% increase in volume. This isostructural transition was a reversible process with a hysteresis of about $6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Completely different behaviors observed using helium media suggest that the small helium atom can penetrate into the cage structure of clathrate on compression. Present experimental results will provide useful information to consider the interaction of $\mathrm{Si}{\mathrm{O}}_{2}$ cages and guest molecules in the clathrate structure.

In situ proton NMR spectra and ${T}_{1}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}$ and ${T}_{2}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}$ relaxation rates of filled-ice hydrogen hydrates at pressure reveal fast translational motion of the ${\mathrm{H}}_{2}$ molecules within the ice frameworks. The NMR spectra to $3.6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ gave surprisingly narrow resonances of the ${\mathrm{H}}_{2}$ guests. Pressure effects on ${T}_{1}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}$ and ${T}_{2}^{\phantom{\rule{0.2em}{0ex}}\ensuremath{-}1}$ of the ${\mathrm{H}}_{2}$ indicate that molecular rotation and diffusion contribute together to the relaxation, from which correlation times ${\ensuremath{\tau}}_{\mathrm{rot}}$ and ${\ensuremath{\tau}}_{\mathrm{dif}}$ were separately determined. Liquidlike fast diffusion of the ${\mathrm{H}}_{2}$ with little pressure sensitivity was deduced from ${\ensuremath{\tau}}_{\mathrm{dif}}$, indicating that the ice framework allows active guest translation even in extensively compressed states.

The new filled skutterudite TbFe 4 P 12 has been prepared at around 4 GPa and 1050 °C. Powder X-ray diffraction of TbT 4 P 12 (T = Fe and Ru) has been studied with synchrotron radiation at ambient pressure. The crystal structures of both compounds were refined by Rietveld methods at ambient pressure. The positional parameters, bond lengths and bond angles have been obtained for TbT 4 P 12 (T = Fe and Ru). The electrical and magnetic properties of TbFe 4 P 12 have been investigated at low temperatures. The susceptibility of this phosphide follows a Curie-Weiss behavior at higher temperatures. The linear slope of the Χ -1 vs. T curve from 15 to 300 K yields an effective magnetic moment of 9.48 μ B . This value is close to the magnetic moment of the Tb 3+ ion calculated from Hund's rule, 9.72 μ B . The ferromagnetic transition of TbFe 4 P 12 was observed at around 10 K, and an electrical anomaly based on the magnetic ordering was detected. The relationship between the crystal structure and the physical properties of TbT 4 P 12 (T = Fe and Ru) is discussed.

Progress in experimental studies to clarify the nature of the discontinuities in the Earth's mantle is reviewed. Developments of high-pressure and high-temperature experimental techniques played an essential role to extend studies to deeper parts of the mantle. Studies on analog materials also played an important role, particularly to clarify the nature of 410 km and 660 km discontinuities, but the experiments on the real material lead to the most unexpected discoveries and conclusive results. Findings of the modified-spinel phase and the post-perovskite phase are good examples. Developments of high-pressure and high-temperature in situ X-ray diffraction using a laser-heated diamond anvil combined with synchrotron radiation dramatically extended the pressure range of the experiments and led to the discovery of the post-perovskite phase at a condition corresponding to the bottom of the mantle. For findings of the post-perovskite phase, various computer simulations also played a very important role once experimental evidence of the phase transition had been obtained.

Micron-sized diamond anvils with a 3 μm culet were successfully processed using a focused ion beam (FIB) system and the generation of high pressures was confirmed using the double stage diamond anvil cell technique. The difficulty of aligning two second-stage micro-anvils was solved via the paired micro-anvil method. Micro-manufacturing using a FIB system enables us to control anvil shape, process any materials, including nano-polycrystalline diamond and single crystal diamond, and assemble the sample exactly in a very small space between the second-stage anvils. This method is highly reproducible. High pressures over 300 GPa were achieved, and the pressure distribution around the micro-anvil culet was evaluated by using a well-focused synchrotron micro-X-ray beam.

Phase relations of garnet with variable compositions were studied using different types of high pressure apparatus and synchrotron radiation. The results of in situ X-ray observations and transmitting electron microscope (TEM) analysis of the recovered samples revealed that garnet first breakdown into an assemblage consisted of aluminous perovskite and other phase (s) under the lower mantle condition. The solubility of aluminum into the perovskite phase is likely to be enhanced by pressure and an existence of iron and calcium.

High pressure in situ x-ray observations of silica (cristobalite) clarified very large effect of non-hydrostaticity on the crystal structure of high pressure polymorph and the apparent compressibility. Under quasi-hydrostatic compression, cristobalite transformed to a new polymorph, which gives very similar diffraction profile to that of stishovite, while under strongly non-hydrostatic compression, a completely different phase named "X-I" was formed. Very different compression curves of cristobalite were observed, depending on the hydrostaticity of applied pressure, which is well explained using the elastic theory.

High pressure in situ X-ray diffraction measurements have been carried out using Drickamer-type high pressure apparatus. Observations were made in two independent directions relative to the compression axis. Observed strains varied systematically in the two directions depending on the Miller indices of the diffraction lines. These systematic variations can be explained by the combined effect of uniaxial compression and the elastic anisotropy of crystals. Present results indicate that careful analysis is required to derive pressure value and equation of state from in situ X-ray diffraction study.

Three phase transitions in MnO are newly found through in situ X-ray observation up to about 140 GPa using diamond anvil cell combined with synchrotron radiation. The rhombohedral distortion from B1 structure at 30 GPa continues to the next phase transition at 90 GPa. A change of the X-ray pattern is also observed at about 120 GPa and its crystal structure is successfully explained by B8 (NiAs) structure. The phase above 90 GPa is expected to be metallic from the highly reflective nature.

Breakdown reaction of natural garnet was studied by an in situ x-ray observation using an MA8-type multi-anvil apparatus up to about 32 GPa. Natural garnet with a composition (Mg0. 72Fe0. l7Ca0. 11) 3Al2Si3O12 breaks down at a pressure between 24 and 27 GPa to a mixture of sub-aluminous orthorhombic silicate perovskite, stishovite, Al-rich phase with unknown structure, and possibly CaSiO3 perovskite. The unreacted garnet was observed even after heating the sample at 31. 7 GPa and 2000 K for 6000 sec. This result implies that the transition rate of the garnet is lower than that of Al-free system such as olivine and pyroxene.

We develop a solid solution ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{Na}}_{x}\mathrm{Ir}{\mathrm{O}}_{3}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.37)$, which exhibits a filling-control metal-insulator transition on a quasi-two-dimensional lattice. The carrier doping into the $S=1∕2$ antiferromagnetic Mott insulator $\mathrm{Ca}\mathrm{Ir}{\mathrm{O}}_{3}$ destabilizes the magnetic long-range order, culminating in a paramagnetic state at $xg0.30$, with simultaneous change from insulating to metallic behavior. The temperature $(T)$ dependence of the resistivity for metallic samples $(0.31\ensuremath{\leqslant}x\ensuremath{\leqslant}0.37)$ exhibits several characteristic features: (1) a ${T}^{\ensuremath{\alpha}}$ dependence with $\ensuremath{\alpha}\ensuremath{\sim}1.2$ in a metallic range, (2) $\mathrm{ln}\phantom{\rule{0.2em}{0ex}}T$ dependence in a weak-localization regime, and (3) positive magnetoresistance violating Kohler's rule. These observations offer a solid foundation to unravel anomalous properties in the normal state of high-${T}_{c}$ cuprates.

Synchrotron X-ray diffraction measurements confirmed that a new polymorph of FeAlO3 could be synthesized at about 1800 K and 72 GPa. This phase can be indexed on an orthorhombic cell and transforms into the trigonal form on release of pressure. The c/a ratio of about 2.71 of the trigonal phase suggests corundum structure of FeAlO3 rather than LiNbO3 or ilmenite structure. This conclusion also suggests that the high-pressure orthorhombic phase could be the Rh2O3(II) structure rather than the GdFeO3-type perovskite structure.

The tetragonal hollandite structure (KAlSi3O8 hollandite) has been studied up to 32 GPa at room temperature using high-pressure in-situ X-ray diffraction techniques. A phase transformation from tetragonal I4/m phase to a new phase was found to occur at about 20 GPa. This transition is reversible on release of pressure without noticeable hysteresis and hence this new high-pressure phase is unquenchable to ambient conditions. The volume change associated with the transition is found to be small (not measurable), suggesting a second order transition. The diffraction pattern of the high-pressure phase can be indexed in a monoclinic unit cell (space group I2/m), which is isostructual with BaMn8O16 hollandite. The {gamma} angle of the monoclinic unit cell increases continuously above the transition. A Birch-Murnaghan equation of state fit to pressure-volume data obtained for KAlSi3O8 hollandite yields a bulk modulus K0 = 201.4 (7) GPa with K'0 = 4.0.

International audience; The results of x-ray diffraction data of a polycrystal under nonhydrostatic compression are analyzed for lattice preferred orientation and stress using lattice strain theories with an application to hcp-Co deformed up to 42.6 GPa in the diamond anvil cell. We obtain a pure 001 fiber texture that develops primarily between 0 and 15 GPa. We also show that for hcp metals the hypothesis of uniform stress across grains and lattice planes cannot be applied. This implies that the effective single crystal elastic moduli deduced from x-ray diffraction under Reuss or geometric averages consistently differ from those measured with other techniques, even after including effects of lattice preferred orientations. These results can be interpreted as an hkl -dependent effective differential stress resulting from plastic deformation.

[1] Polycrystalline CaIrO3 phase, synthesized in a cubic-anvil type high pressure apparatus at 4 GPa and 1473 K, has been investigated using transmission electron microscopy (TEM). Individual crystallites have a platy crystal habit elongated parallel to the crystallographic a-axis, which is the direction of the edge-shared octahedral chain. The dislocations with Burgers vectors b = [100] and 〈u0w〉 nucleated in the CaIrO3 phase during the synthesis experiments. The potential slip plane could be (010), the most likely having with the (010)-layered structure of IrO6 octahedrons. The crystal morphology and dislocation microstructures of CaIrO3 should provide important constraints for the discussion of the deformation behaviour and polarization anisotropy of the post-perovskite phase in the lowermost mantle.

A compound ZrRuP was prepared with a wedge-type cubic-anvil C.gh pressure apparatus at around 4 GPa and 1400°C. The X-ray diffraction pattern of ZrRuGe prepared at high pressure is assigned by the index of the TiFeSi-type structure. The resistivity of the compound decreased slowly with decreasing temperature, and sharply dropped at around 11 K. The superconducting transition temperature (Tc) of 11 K is the highest one obtained during various sample preparations and the annealing conditions. The Tc's observed for ZrRuGe are between 8 and 11 K. The Tc of ZrRuGe decreased rapidly with increasing applied magnetic field. The upper critical field(Hc2) obtained from the Hc2 vs. temperature curve was 0.5 tesla at 0 K when the midpoint was taken as the Tc. The superconductivity of the compound ZrRuGe is discussed.

High-pressure in situ x-ray diffraction and transmission electron microscopy on quenched samples show that natural garnet transforms to orthorhombic perovskite (and minor coexisting phases) containing increasing amounts of aluminum with increasing pressure. This suggests that the perovskite is the dominant host mineral for aluminum in Earth's lower mantle. Orthorhombic perovskite is quenched from ∼35 gigapascals but, because of the increased aluminum content, transforms to the LiNbO 3 structure upon quenching from ∼60 gigapascals.

[1] We report here new data on pressure dependence of Fe-Mg partitioning between (Mg, Fe)SiO3 perovskite (Pv) and magnesiowustite (Mw), KPv/Mw, and (Mg, Fe)SiO3 post-perovskite (PPv) and Mw, KPPv/Mw, up to 123.6 GPa at 1600 K measured by synchrotron X-ray diffraction method and analytical transmission electron microscopy (ATEM). We observed a high FeO content in PPv coexisting with Mw [KPPv/Mw = (FeO/MgO)PPv/(FeO/MgO)Mw = 0.30] compared to that in Pv [KPv/Mw = (FeO/MgO)Pv/(FeO/MgO)Mw = 0.12] observed from 23.0 to 95.4 GPa. KPv/Mw keeps a constant value of 0.12 up to the PPv phase boundary. Our results also support the possibility that a metallic phase may form in the lower mantle. The assemblage of PPv and Mw is 1.5–1.7% denser than the Pv bearing assemblage, which results in a gravitational stabilization of the lowermost mantle.

The behavior of negative thermal-expansion material scandium molybdate Sc2(MoO4)3 is investigated at high pressure (HP) and high temperature (HT) using x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The compound exhibits unusually high compressibility (bulk modulus ~6 GPa) and undergoes amorphization at 12 GPa. On the other hand, in situ laser heating of amorphous samples inside the diamond-anvil cell is found to result in crystalline diffraction pattern and Raman spectrum different from those of the original compound. Upon release of the pressure subsequent to laser heating, the Raman spectrum and the diffraction pattern remain unchanged. Matching of several of the diffraction lines and Raman peaks in the laser-heated samples with those of MoO3 suggests a solid-state decomposition of the parent compound under HP-HT conditions into MoO3 and other compounds. Other diffraction lines are found to correspond to Sc2Mo2O9, Sc2O3, and the parent compound. Quantitative analysis of the characteristic x-ray emission from different regions of the sample during scanning electron microscopic observations is used for obtaining the compositions of the daughter compounds. The stoichiometries of two main phases are found to be close to those of MoO3 and Sc2Mo2O9. These results support the model that the pressure-induced amorphization occurred in this system because a pressure-induced decomposition was kinetically constrained.

The soft transverse acoustic mode of TeO2 has been investigated in detail by the microscopic Brillouin scattering in the backward geometry as a function of pressure. Both of quasi-transverse mode (T′) and quasi-longitudinal mode (L′) have been measured from 1 atm to 1.6 GPa (transition pressure Pc = 0.9 GPa) using Diamond Anvil Cell for phonons with various propagation directions at different angles of 7.6°, 4° and 2.3°, respectively, from [110]-direction. The T′-mode for 2.3° decreased till the lowest value ∼1.37 GHz at Pc. The L′-mode showed no dramatic change. We will explain these results according to a Landau theory of the ferroelastic transition under pressure.

[1] In situ X-ray diffraction measurements have been made on KAlSi3O8 hollandite using diamond anvil cell and multianvil apparatus combined with synchrotron radiation. Both of the measurements with different techniques demonstrated that K-hollandite transforms to a new high-pressure phase (hollandite II) at ∼22 GPa upon increasing pressure at room temperature. The X-ray diffraction peaks of the new phase were reasonably indexed on the basis of a monoclinic cell with I2/m space group. Hollandite II was also confirmed to be formed at high temperatures to 1200°C and pressures to 35 GPa, which was quenched to room temperature under pressure but converted back to hollandite at about 20 GPa on release of pressure. The present result is contradictory to earlier studies based mainly on quench method, which concluded that hollandite is stable up to 95 GPa at both room temperature and high temperatures up to 2300°C.

[1] We have developed synchrotron X-ray diffraction techniques for studying the structure of silicate melts and have applied them to measuring the structures of MgSiO3 and CaSiO3 melts up to 6 GPa. In both melts, it appears that the changes in the local structure around the divalent ions and in the network structure of SiO4 tetrahedra are the dominant compression mechanisms while a change in the local structure around the Si ion is a secondary mechanism up to at least 6 GPa. The structural changes appear to be larger in CaSiO3 melt than in MgSiO3 melt, especially in the vicinity of ambient pressure. These results are consistent with available experimental and theoretical information on MgSiO3 and CaSiO3, and explain discrepancies in previous work.