Search

A new multicomponent A-site ordered perovskite-type oxide has been successfully synthesized in the BiFeO 3 and MnTiO 3 pseudobinary system at high pressure and temperature, 6 GPa and 1300 K. It is found that the oxide is an A-site ordered and B-site disordered perovskite Bi 3+ Mn 2+ 3 (Fe 3+ 0.25 Ti 4+ 0.75 ) 4 O 12 in the space group of the cubic high symmetry Im -3 with a lattice parameter a =7.5937(3) A. It should be noted that the Mn 2+ ions in the A ′-site show a site-splitting, while the Bi 3+ ones are in a regular icosahedron position of the A -site. On the other hand, the Fe 3+ and Ti 4+ ones in the B -site are disordered in this perovskite structure. The temperature dependence of magnetizations and specific heats at low temperatures shows spin-glass-like behaviors below 11 K.

Nb hydrides formation in 10-GPa supercritical water has been investigated by angle-dependent micro-beam hard X-ray photoemission spectroscopy. In the Nb 3d core-level spectra, Nb hydride components are found in the slightly high binding energy side of the metallic components, and the oxide ones are observed even though little oxides are recognized in X-ray diffraction patterns. Obtained emission-angle dependence of the Nb 3d core-level spectra of Nb hydride specimens shows that the Nb hydride components increase with the emission angle decreased i.e. the sampling depth increased, while the oxide ones decrease. The bulk valence-band spectrum is obtained by decomposing the measured valence-band spectra into a bulk and surface components with use of the emission-angle dependence of the core-level and valence-band spectra; it consists of two bands. This implies the Nb–H chemical bond formation and Nb in an oxidation state, consistent with reported band structure calculations and the observed core-level chemical shifts. Thus it is confirmed by valence-band and core-level photoelectron spectroscopy that the Nb hydrides are formed inside the specimen, irrespective to the well-known high oxidation ability of supercritical water.

We have characterized Nb hydrides synthesized in high-pressure supercritical water by hard X-ray photoelectron spectroscopy. Comparison is made, in particular, of the Nb 2p core level spectra and valence band ones for the Nb hydride specimens in different stages of hydrogenation with those for Nb oxide and metallic references. The Nb 2p core level spectra of the Nb hydride specimens synthesized at relatively low temperature show an intense Nb 2 O 5 component and a shoulder structure, which is attributed to Nb hydrides, at the high binding energy side of a metallic component of the Nb metal. The valence band spectra of the Nb hydride specimens also show a broad band at the binding energy E B between 5 and 9 eV, which is ascribed mainly to Nb oxides. The present results indicate that the surface of the synthesized Nb hydrides is covered with several 10 nm thick Nb oxides and suggest that the Nb hydrides are formed deep inside the specimens. The Nb 2p chemical shift implies the Nb valence of +1.4 for the synthesized hydride NbH x .

In order to verify pressure scales of gold, the atomic-volume dependence of Debye temperature under high pressure up to 14 GPa was measured based on Debye–Waller factor by an X-ray diffraction method. High-pressure and high-temperature X-ray powder diffraction patterns were collected by an energy-dispersive method using synchrotron radiation. The X-ray Debye temperature under high pressure was calculated from the integrated intensity ratio between the diffraction patterns collected at two different temperatures. The atomic-volume dependence of the Debye temperature obtained in the present study was consistent with that predicted by a first-principles calculation, in which Debye temperature and Gruneisen parameter of the volume at ambient condition were Θ D 0 = 180 K and γ 0 = 3.16 , respectively.

High-pressure and high-temperature behavior of Zn(OH)2 with a peculiar orthorhombic structure was examined using the in-situ X-ray powder diffraction method. Two high-pressure phases were observed by elevating temperature up to 400 ∘C at ca. 15 GPa. One was a new high-pressure and high-temperature phase discovered at 14.5 GPa and 300 ∘C, and the X-ray diffraction pattern could be indexed on an orthorhombic cell. The other was observed at 14.2 GPa and 400 ∘C and it had the hexagonal CdI2-type structure. The phase was finally quenchable to the ambient condition. The volume of the CdI2-type phase was 22.8% smaller than that of the peculiar orthorhombic phase at ambient condition. The bulk modulus was determined to be K 0 = 46.7 (2.6) GPa and K ′ = 8.6 (1.1). The c -axis was more compressive than the a -axis. The anisotropic behavior of Zn(OH)2 with the CdI2-type structure was consistent with that of other hydroxides.

High-pressure and high-temperature behavior of MgF2 was observed up to 15 GPa and 750 ∘C by an in-situ X-ray diffraction method. The single phase with the α-PbO2 type structure was obtained at 12.7 GPa and 750 ∘C. The phase was almost quenchable to ambient condition. Its orthorhombic cell parameters were a 0 = 4.590 ( 1 ) A , b 0 = 5.555 ( 1 ) A and c 0 = 5.048 ( 1 ) A and its volume per chemical formula was 1.1% smaller than that of the rutile phase at ambient condition. MgF2 was confirmed to have a stable region for the phase at around 13 GPa and 600 ∘C and to have the rutile–CaCl2–α-PbO2–PdF2 type phase transition series under high pressure and high temperature, as predicted by a previous theoretical calculation method. The bulk modulus of the α-PbO2 type phase was determined to be K 0 = 98.0 ( 7 ) GPa .

High-pressure and high-temperature behavior of ZnF2 with the rutile-type structure was investigated using an energy-dispersive-type X-ray diffraction method. Two high-pressure phases were found in the range up to 15 GPa and 400 ∘C. The CaCl2-type phase with an orthorhombic cell (space group: Pnnm) was clearly observed at 5.4 GPa and 400 ∘C. Further phase transition was induced above 10 GPa at room temperature. The single phase of the high-pressure phase was obtained at 15.3 GPa and 350 ∘C. The high-pressure phase was found to have the PdF2-type structure with a cubic cell (space group: Pa-3). The single phase was observed above 4 GPa in a pressure-release process at room temperature, and completely reverted to a mixture of the rutile-type phase and the α - PbO2-type phase at ambient condition. The high-pressure behavior of ZnF2 was similar to that of MgF2.

We determined the structural changes in CaSiO 3 and CaMgSi 2 O 6 glasses recovered from high pressure and temperature conditions (up to 7.5 GPa and 500 °C) using X-ray diffraction, Raman, infrared and X-ray emission spectroscopy. Densities of the metasilicate glasses increase with applied pressure at high temperature; CaMgSi 2 O 6 glass is more compressed than CaSiO 3 glass when recovered from 7.5 GPa and 500 °C. We propose a mechanism for densification of these glasses, that is mainly due to the compaction in medium-range scale (i.e. decrease in cluster size of SiO 4 anionic units with Ca, Mg polyhedra). Reduction of Si–O–Si bond angle is very small in the recovered CaSiO 3 and CaMgSi 2 O 6 glasses, as previously suggested.

Pressure-induced phase transitions are one of the most interesting fields in high-pressure research. The X-ray powder diffraction method is useful to detect such phase transition, although it can not provide information about the diffraction direction. Therefore the process of indexing the X-ray powder diffraction pattern of the high-pressure phase is the most important, because even the crystal system of the phase can not be determined without this process. Both classic and modern indexing methods for X-ray powder diffraction patterns are reviewed in this article. Several successful results are also introduced, using a computer code called “DICVOL91” for the indexing method.

High-pressure and high-temperature behavior of ZnSe was investigated by energy dispersive X-ray diffraction method up to 14 GPa and 800°C. A new high-pressure phase with B9 (HgS)-type structure is found near the B3–B1 phase boundary at room temperature, as predicted by an ab-initio calculation. The property and observed pressure region of the B9-type phase are in good agreement with the ab-initio calculation. At high-temperature condition above 300°C, only the direct transitions are observed between the B3 and B1 phases. The B3–B1 phase boundary is also determined to be P (GPa)=12.21−0.0039 T (°C) for the temperature range between 300 and 800°C.

High-pressure phase transition of Ta 2 NiO 6 with the trirutile-type structure was investigated from the viewpoint of crystal chemistry. A new quenchable high-pressure phase was found in the pressure range higher than 7 GPa and 900°C. The high-pressure phase has an orthorhombic cell ( a =4.797(1) A, b =5.153(2) A and c =14.85(1) A and space group; Abm 2), and it is more dense by 9.6% than the trirutile-structured phase. Infrared spectra of the trirutile-type phase and the high-pressure phase show that Ni 2+ ions in the high-pressure phase are still in octahedral sites. The crystal structure of the high-pressure phase is considered as a cation-ordering trifluorite-type structure, which can be stabilized by a crystal field effect of Ni 2+ ions.

The high-pressure and high-temperature behavior of V 2 O 5 with a layered-orthorhombic structure was studied by both in-situ X-ray diffraction observations and recovery experiments. Two quenchable high-pressure phases (HPP1 and HPP2) were observed in the pressure and temperature range up to 11 GPa and 700°C. The phase transition to the HPP1 was observed by elevating the temperature above 300°C in the pressure range up to 7GPa. The HPP1 was found to have an orthorhombic cell (a = 7.100(7) A, b = 6.294(5) A and c = 3.578(2) A at 0.1 MPa and 27°C). The phase transition to the HPP2 was also observed in an elevating temperature process above 9 GPa. Unit cell parameters of the HPP2 have not yet been determined.

We report a “ship-in-a-bottle” synthesis where encapsulation of copper phthalocyanines (CuPc) into mesoporous channels of silicate MCM-41 was achieved by chemical vapor deposition (CVD) using 1,2-dicyanobenzene (DCNB). Silanol protons of MCM-41 were ion-exchanged with copper ions before CVD, and when the initial amount of DCNB was much larger than that of copper ions, CuPc molecules in the channels were found to form a cofacial structure that was confirmed by diffuse reflectance spectra.

High-pressure and high-temperature behavior of FeS was investigated up to 16 GPa and 750°C . A temperature-induced phase transition was observed at 4.6 GPa. The NiAs type phase was stable above 420°C, and it transformed to its super-structured phase with a hexagonal cell below 420°C in a temperature cooling process. The phase transition could be explained as a second-order transition, based on the analysis of X-ray diffraction intensities from the super-lattice.

A temperature-induced second-order phase transition of FeS was observed at 4.6 GPa. The NiAs type phase was stable at 500°C, and it transformed to its super-structured phase with a hexagonal cell near-by 420°C in a temperature cooling process. An abnormal temperature behavior of the c -axis causes an unusually low thermal expansion of FeS in this pressure range, and they can be explained by a relaxation of a repulsion along the c -axis in the hexagonal phase.

Pressure induced B4 (wurtzite) -B1(rocksalt) transition of ZnO was investigated by energy dispersive X-ray diffraction method up to 12GPa and 1000°C. The phase boundary between the B4 and B1 phases can be described by a straight line with P/GPa=6.1-0.0012*T/°C. Under non-hydrostatic condition, the phase transition at 27°C is reversible with a large hysteresis about±4.0GPa, and the high pressure phase with the B1 structure is unquenchable at ambient condition. On the other hand, the B1 type high pressure phase is quenchable under hydrostatic condition. The unit cell parameter of the B1 phase at 0.1MPa and 27°C is determined to be a=4.2783(3)A. Bulk moduli of the B4 and B1 phases at 27°C are determined to be 128.4±0.9GPa and 197±3GPa, respectively. Furthermore, an anisotropic compression behavior of the B4 type ZnO is observed, in which the c axis of the B4 type structure is slightly more compressible than that of the a axis.

High pressure and temperature behavior of stoichiometric FeS (troilite) was studied up to 16 GPa and 800 °C using a combination of a large volume press apparatus and a synchrotron X-ray source. A pressuretemperature phase diagram of FeS was determined from more than 200 data points. The phase diagram shows that there are four stable phases; the troilite phase, the hexagonal phase, the NiAs type phase and the high pressure phase with a monoclinic cell. In the compression curve of FeS at 300 °C, an inflection was observed at 7.5 GPa. Minimum value of cubical expansion under high pressure was also observed around 6 GPa. These results suggested an electronic transition of the hexagonal phase between 6 and 8 GPa. The transition might explain a curved boundary between the hexagonal phase and the monoclinic high pressure phase.

Shock-synthesis experiments of REBa 2 Cu 3 O y (RE=Y, Eu, and La) were carried out for the mixture of component oxides as starting materials using a 25 mm-bore propellant gun. Both tetragonal EuBa 2 Cu 3 O y with c / a =3.00 and cubic LaBa 2 Cu 3 O y were successfully synthesized by shock compression, but YBa 2 Cu 3 O y was synthesized only partly. The optimum condition for obtaining maximum yield of shock-synthesized EuBa 2 Cu 3 O y and LaBa 2 Cu 3 O y was shock compression of the starting materials with 40% porosity to 30 GPa. La 1+ x Ba 2− x Cu 3 O y could also be synthesized, but Eu 1+ x Ba 2− x Cu 3 O y could not. Shock-synthesized EuBa 2 Cu 3 O y and LaBa 2 Cu 3 O y were in a metastable phase in which RE 3+ and Ba 2+ were not ordered perfectly; they converted to the phase synthesized by conventional solid state reaction when annealed above 900°C. Only after annealing above 900°C, followed by oxidation at 400°C, did EuBa 2 Cu 3 O y exhibit superconductivity with T c ≒71 K. These results suggest that shock synthesis of REBa 2 Cu 3 O y becomes easier with a decrease in the difference between ionic radii of RE 3+ and Ba 2+ .

Compression behavior of FeS at room temperature up to 15 GPa is investigated using a combination of a synchrotron white X-ray source and a large volume press (MAX80). Two high pressure phase transitions at 3 and 7 GPa are reconfirmed. The high pressure phase between 3 and 7 GPa can be explained by a MnP type related structure. From 26 diffraction lines at 10.30 GPa, unit cell dimensions of the higher pressure phase, of which the crystal structure has been unknown, are determined to be a = 8.044(3) A, b = 5.611(2) A, c = 6.433(4) A, β = 93.11(4)° and Z = 12 for a monoclinic system. Possible space group for the cell is P2 1 or P2 1 /m, and there are multi-sites for iron atoms in the cell. The cell dimensions show that the higher pressure phase still has a NiAs type framework in the structure. The high pressure phase is about 6% denser than the MnP type phase at 7 GPa, and is estimated to be 12% denser than the troilite phase at ambient condition. © 1997 Elsevier Science Ltd. All rights reserved

Shock compression experiments on single crystal MnO grown by the Verneuil method have been carried out for the pressure range of 41–114GPa using both propellant and two-stage light-gas guns. The shock states, recorded with the inclined mirror method, were analyzed by the free-surface approximation and impedance-match solution. The observed shock compression curve of MnO with the rock salt structure(B1) is found to be slightly more compressible than that measured statically to 60GPa using a diamond-anvil cell. We observed a phase transition around 90GPa with a volume decrease of approximately 8%. The present phase transition pressure falls on a trend of B1-B2(CsCl-type structure) transformation among alkaline earth metal monoxides, rather than transformation to the B8(NiAs-type structure) that wustite (FeO) demonstrates.

Inclined‐mirror Hugoniot measurements of yttria (Y2O3) ‐doped (9.6 and 8.0 mol %) cubic zirconia single crystal and polycrystal were performed in the pressure range up to 120 GPa to study yielding and phase transition. The Hugoniot‐elastic limit (HEL) stresses parallel to the 〈100〉 and 〈110〉 axes were approximately 14 and 25 GPa, respectively, while that of the polycrystal was approximately 13 GPa. Above the HELs the Hugoniot data parallel toward the 〈100〉 and 〈110〉 axes converged on each other, and showed large relief to an isotropic compression state, while those of the polycrystal preserved a considerably larger shear strength. A phase transformation took place at approximately 53 GPa (both 〈100〉 and 〈110〉 axis directions), and was completed by about 70 GPa. The phase transition pressure was much higher than those of the monoclinic‐ or tetragonal‐orthorhombic II phase transitions under static compression. The shock velocity Us versus particle velocity Up relation of the final phase of the single crysta...

In situ observation of the structural changes in the eutectic Au-Ge and Ag-Ge alloys was carried out under the combined conditions of high pressure and temperature by synchrotron X-ray diffraction. In the alloys with compositions near to the eutectic composition, the initial two-phase state of α (primary solid solution of Au or Ag) and β (primary solid solution of Ge) has been converted to a single-phase state of ζ, an intermediate phase with a hexagonal close-packed structure with an axial ratio close to the ideal value. A possible form of the phase diagram for the two alloy systems at a pressure of 7 GPa has been constructed on the basis of the results of the in situ observation and high-pressure quenching experiment.

In situ observation of the structural changes in the eutectic Au-Ge and Ag-Ge alloys was carried out under the combined conditions of high pressure and temperature by synchrotron X-ray diffraction. In the alloys with compositions near to the eutectic composition, the initial two-phase state of α (primary solid solution of Au or Ag) and β (primary solid solution of Ge) has been converted to a single-phase state of ζ, an intermediate phase with a hexagonal close-packed structure with an axial ratio close to the ideal value. A possible form of the phase diagram for the two alloy systems at a pressure of 7 GPa has been constructed on the basis of the results of the in situ observation and high-pressure quenching experiment.

Sintered specimens of cubic Sc2O3-type structure (C-type, Ia 3 ), Sc2O3, Y2O3, Sm2O3, and In2O3, and monoclinic Sm2O3-type structure (B-type, C2 m ) Sm2O3, and powdered specimens of C-type Gd2O3 were shock-loaded to 2–50 GPa using flyer plates accelerated by a propellant gun. Recovered specimens were studied by X-ray powder diffraction analysis at room and high temperature. Y2O3 began to transform to the B-type structure above 12 GPa, and the transformation was completed at 20 GPa. Gd2O3 also transformed to the B-type structure, but residual temperature effects were observed in the yield and crystallinity of the high pressure phase. In2O3 transformed to the corundum structure ( R 3 c ) in the pressure range of 15–25 GPa, although the yield was very small. Shock-induced phase transition from the C-type to the B-type structure was inferred to proceed via hexagonal La2O3-type structure (A-type, P 3 m1 ), in comparison with static high pressure experiments.

High pressure structural change of an obsidian from Iceland has been investigated using X-ray radial distribution function (RDF) analysis and Raman spectroscopy. Obsidians have been compressed under 4 GPa at 20°C and 500°C by a cubic anvil apparatus. The obsidian treated under 4 GPa-20°C condition shows almost the same density and RDF curve as the original obsidian. However, the permanent densification of about 9% was observed by the compression under 4 GPa-500°C Based on RDF and Raman analyses, the structure of obsidian may change in the dominant TO4 (T=Si and Al) from 5 and 6 to 4 and 3 membered rings by the compression at 500°C.

Rutile type MnF2 was shock‐loaded to 3.6 – 33.4 GPa by impact of flyer plates accelerated by a propellant gun. Recovered samples were studied by X‐ray powder diffraction and transmission electron microscope (TEM). The phase transition of rutile type to the α‐PbO2 type structure was found in the recovered sample. The yield of α‐PbO2 phase in the recovered sample increases up to about 10 GPa, and decreased at high pressures. The XRD line width of rutile phase (110) also has maximum at pressure of 10 GPa, and that of α‐PbO2 phase (111) is broader than rutile phase and almost constant against shock pressure. The lamellae pattern, which consists of two crystal phases (rutile and α‐PbO2 phase), was observed in the shock recovered sample from 8.3 GPa by TEM.

A high-pressure phase of TiO(2), which had been observed by shock-wave experiments and remained unresolved, has been studied by in situ x-ray diffraction. The single phase was formed at 20 gigapascals and 770 degrees C with the use of sintered-diamond multianvils; it has the same structure as baddeleyite, the stable phase of ZrO(2) at ambient conditions. The coordination number of Ti increases from six to seven across the rutile to baddeleyite transition, and the volume is reduced by approximately 9 percent.

Shock‐loading experiments were done for as‐prepared nonsuperconducting specimens of Tl2Ba2CuO6. The shocked specimens which were encased in the stainless‐steel container with small holes exhibited a superconductivity of about Tc−75 K at 18 GPa, indicating that the overdoping state was released by oxygen loss during shock‐loading. The x‐ray powder diffraction pattern of the recovered specimens after shock‐loading showed broadening of diffraction lines and a distortion to the orthorhombic symmetry. A transmission electron microscope image of the shocked specimen in which the orthorhombic distortion was observed in the x‐ray powder diffraction patterns showed a twin structure.

Shock compression measurements of MnO have been carried out up to 120 GPa, and a phase transition with a volume decrease, -ΔV/V 0 , of about 6 percent is observed at 90 f 3 GPa. Release adiabat measurements revealed that the high pressure phase was retained down to 37 GPa and the volume difference with respect to the rock salt (B1) phase was estimated to be about 23 percent. The observed large volume change in the phase transition of MnO excludes the possibility of the nickel arsenide (B8) structure for the high pressure phase, unlike the high pressure phase of Fe 1-x O. The cesium chloride (B2) structure is suggested to be a possible candidate from the systematics obtained for the B1-B2 transformation in alkaline earth monoxides, although the observed volume change would be too large. Furthermore, a possibility of change in the electronic configuration of transition metal ions at very high pressures, such as spin-pairing transition, is also inferred to assess the observed large volume change in MnO.

High-pressure behavior of FeS up to 16 GPa and 800°C is investigated by energy-dispersive type X ray powder diffraction method. Four phases (the troilife phase, MnP-related phase, NiAs type phase, and a high-pressure phase) are observed in this pressure and temperature range. The high-pressure phase at 10.30 GPa and 27°C, the structure of which has been unknown, can be indexed on a monoclinic system: α=8.044(3)A, b=5.611(2)A, c=6.433 (4)A, β=93.11(4)°, and Z=12. The high pressure phase is calculated to be 12% denser than the troilite phase at ambient conditions. All these four phases are found to have an NiAs-type framework in their structures. Phase equilibria of FeS are determined by paying attention to diffraction lines with d-spacings larger than 3A, due to a long-range order of the NiAs-type framework. The phase boundary between the MnP-related phase and the simple NiAs-type phase can be described by a straight line (P/GPa = 0.0212 × T/°C - 3.38) in the pressure and temperature range up to 11GPa and 700°C. The result shows that high-pressure behavior of the simple NiAs-type phase may play an important role in the interior of the terrestrial planets.

The crystal structure of a high pressure phase of ZnTe at 11.5 GPa is proposed based on energy dispersive x‐ray powder diffraction patterns using a DIA type device (SAM‐85). Its unit cell parameters are a=4.045(1) A and c=9.342(4) A for a hexagonal lattice. Its space group is P31, and positional parameters of Zn and Te atoms are (0.35, 0.20, 0.00) and (0.49, 0.49, 0.47) in 3a site, respectively. The crystal structure can be understood as an intermediate structure between the zinc blende structure and the rock salt. The property of the structure can be explained by a strong tetrahedral site preference of Zn.

Pressure behavior of ZnTe at room temperature was studied using an X-ray energy dispersive method on a DIA type cubic anvil apparatus (SAM-85) at NSLS-X17B1. By using powdered polyethylene, the sample and NaCl for a pressure scale were held under quasihydrostatic conditions, which were confirmed by X-ray diffraction method. Two high-pressure phase transitions were confirmed using X-ray powder diffraction simultaneously with electrical resistance measurements. The phase transition pressures under quasihydrostatic conditions were determined to be 9.6 GPa, at which the resistance increased, and 12.0 GPa, which was the midpoint of a large resistance decrease. Errors in the pressure determinations were estimated to be less than 0.2 GPa. These pressure values may depend on grain size and anisotropic stress effects on the calibrant. From X-ray observation of ZnTe, the bulk modulus of the zinc blende structure was calculated to be K 0 = 51(3) GPa and K′0 = 3.6(0.8), and the first transition at 9.6 GPa was found to have about 9% volume change. It was consistent with an anomaly in the pressure generating curves.

Pressure-induced phase transitions of Zn(OH)2 were investigated under hydrostatic condition at room temperature by an in-situ X-ray powder diffraction method and a visible observation method for a single-crystalline specimen. Two phase transitions were observed in the pressure range up to 4GPa. The first transition occurred at 1.1 GPa and it was a quick single crystal – single crystal transition. The high-pressure phase 1 with a tetragonal α-cristobalite-related structure was stable up to 2.1GPa. The coordination number of zinc atoms was 4+2. The second phase transition was observed above 2.1GPa. The high-pressure phase 2 was quenchable to ambient condition. The crystal structure has not been determined yet because the X-ray powder diffraction pattern was too broad to be even indexed. Comparison of polymorphs in Zn(OH)2 suggests that the volume per chemical formula of the high-pressure phase 2 is in 40.0 – 44.5 A3 at 2.1 GPa and room temperature and that the coordination number of zinc atoms in the phase is probably 4+2 or 5.

High-pressure behaviour of Ta3Si intermetallic compound was investigated by shock compression and static compression methods. Superconducting phase with TC = 9.3 K was found in the sample shocked to 50-61 GPa, however most of the shock recovered sample indicated the starting stable phase with the Ti3P-type structure. The new superconducting phase was not obtained from static compression up to 15 GPa and 800 ?C. Bulk modulus of Ta3Si with the Ti3P-type structure was determined to be K0 = 246(4) GPa. The present results suggest that a rapid phase transformation occurred during shock compression, but most of the high-pressure phase was reverted to the stable phase in the decompression process.

Polymorphic phase transformations have been found in many substances by shock compression. The transition pressures observed by dynamic and static compression are generally in good agreement, provided that the kinetics of phase changes, such as those which are displacive or electronic in origin, is sufficiently fast to be completed within the short time interval of a shock process. Molecular dynamical calculations of rutile under uniaxial stress showed that the phase transition to high pressure fluorite phase could be completed within a few picoseconds, much shorter than the shock rise time within the shock front. The fact that the phase transition pressures of rutile single crystals depends on the shock loading directions can also be explained, given the uniaxial nature of the plane shock loading within the shock front. On the other hand, there are also many examples in which the recovered materials cannot be considered as due to the shock-induced high pressure phase itself, but metastably formed during the unloading process. To apply the shock wave technique for materials synthesis, the importance of the knowledge on the shock-induced phase transformations as well as pressure-temperature history of shock process is mentioned.

Hugoniot-measurement experiments of the Y2O3-doped (9.6 mol%) stabilized zirconia in the pressure range up to 120 GPa were performed by using single crystals to study cubic directly the yielding property, phase transition and their crystal-axis effects to shock propagation. The Hugoniot parameters were measured by means of the inclined-mirror method combined with a powder gun and a two-stage light gas gun in the impact velocity range of 1.2-3.6 km/s. The Hugoniot-elastic limits (HEL) parallel to (100) and (110) axes showed large difference. Above the HEL’s, the Hugoniot data parallel to (100) and (110) axes converged each other, and showed large relief to an isotropic compression state. In addition, this material transformed to the high pressure phase up to 70 GPa.

Shock loading effects on Bi-Sr-Ca-Cu-O superconductor were studied for the pressure to 10 GPa by TEM/SEM observations and magnetic measurements. Shock deformation of Bi-compounds showed very unique texture of kink bands which were characteristic deformation structure in mica-like compounds. Bi2Sr2CaCu2O8 shocked to 10 GPa showed considerable degradation of Tc in contrast to other superconducting oxides. Annealing of the shocked specimen at 870 C in air for 10 hours recovered superconductivity with improvement in Tc. The comparison of shocked and subsequently annealed specimen by TEM/SEM observation explained the characteristic change in superconductivity.

Shock residual effects on pinning energy of La 1.85 Sr 0.15 CuO 4 (LSCO) and YBa 2 Cu 3 O 7 (YBCO) were examined by measuring the relaxation of diamagnetic magnetization. In both LSCO and YBCO shocked to 11 GPa pinning energy was observed to increase. By annealing of LSCO at 930°C and YBCO at 890°C. ΔM increased from that of unshocked specimens.

We synthesized a homogeneous, tetragonal EuBa2Cu3O y with c/a=3.00 by the shock compression method. The phase is considered to be similar to the tetragonal YBa2Cu3O y metastably formed at relatively low temperature with the c/a ratio=3.00. Electron diffraction patterns indicate ordering of Eu and Ba atoms to some extent, but ordering is presumably not perfect. High resolution trasmission electron microscory images show that shock-synthesized EuBa2Cu3O y consists of 60-80-Å-size domains, whose principal axes are perpendicular to each other. Perfect ordering of Eu and Ba atoms was achieved by annealing the shock-synthesized specimen above 900° C, resulting in the increase of the c/a ratio from 3.00 to 3.05 as well as superconduction upon O2 annealing. This result is explained by the shortness of the reaction time in shock processes.