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Metastable solid electrolytes exhibit superior conductivity compared to stable ones, making them a subject of considerable interest. However, solid-state synthesis of the metastable phase is affected by multiple thermodynamic and kinetic parameters, leading to ambiguity in the categorization of stability and metastability. This study categorizes remnant and intermediate metastability based on thermodynamic principles. The intermediate metastable phase, which is less stable than the temperature-independent stable phase, typically transforms into the stable phase(s) at high temperatures. In contrast, the remnant metastable phase, such as the high-temperature stable phase obtained by fast cooling, becomes the most stable phase, and annealing of the remnant metastable phase causes the phase transition to the low-temperature stable phase. Investigating Li+ conducting chlorides, Li3MCl6 (M = Y and Ho), this study shows that heating starting materials to approximately 600 K produced low-temperature Li3MCl6 phase with one formula unit; high-temperature Li3MCl6 with three formula units were observed by further heating. Annealing of quenched Li3MCl6 at 573 K resulted in a phase transition from high-temperature to low-temperature, indicating that the high-temperature phase was remnant metastable at low temperatures. XRD patterns of low-temperature phases suggest the presence of stacking faults that stabilize low-temperature structures with high symmetry.

We report on the crystal structure and electronic properties of the heavy fermion superconductor UTe2 at high pressure up to 11 GPa, as investigated by X-ray diffraction and electrical resistivity experiments. The X-ray diffraction measurements under high pressure using a synchrotron light source reveal anisotropic linear compressibility of the unit cell up to 3.5 GPa, while a pressure-induced structural phase transition is observed above 3.5-4GPa at room temperature, where the body-centered orthorhombic crystal structure with the space group Immm changes into a body-centered tetragonal structure with the space group I4/mmm. The molar volume drops abruptly at the critical pressure, while the distance between the first-nearest neighbor of U atoms increases, implying a switch from the heavy electronic states to the weakly correlated electronic states. Surprisingly, a new superconducting phase at pressures higher than 7 GPa was detected at Tsc above 2K with a relatively low upper-critical field, Hc2(0). The resistivity above 3.5GPa, thus, in the high-pressure tetragonal phase, shows a large drop below 230 K, which may also be related to a considerable change from the heavy electronic states to the weakly correlated electronic states., Comment: 11 pages, 9 figures

We report our investigations on the effects of pressure on the electronic and magnetic properties of magnetic Dirac semimetal ${\mathrm{EuMnBi}}_{2}$ by using electrical transport, synchrotron x-ray diffraction, and x-ray absorption spectroscopy. The antiferromagnetic interaction due to the Eu magnetic moment in ${\mathrm{EuMnBi}}_{2}$ is enhanced under pressure up to $\ensuremath{\sim}3.9\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. The N\'eel temperature (${T}_{N}$) is found to disappear above 4 GPa and a new transition ${T}_{t}$ at around 29 K emerges above 6 GPa. ${T}_{t}$ remains relatively constant up to 15 GPa, above which it increases with further compression, reaching $\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 22 GPa. Eu $L$-edge x-ray absorption spectroscopy revealed a valence change of Eu toward a trivalent state that begins above 6 GPa, which indicates that ${T}_{t}$ is likely related to the valence transition temperature of Eu. Sign reversal of the Hall resistivity above 7 GPa suggests that the valence change of Eu also induces a Fermi surface modification.

We present the first application of double-stage diamond anvil cells (ds-DACs) to X-ray absorption spectroscopy (XAS) of Rhenium (Re) metal. By using highly stable and sub-micron sized X-ray beam, ...

We present the element-selective local structure analysis of ferromagnetic Fe65Ni35 Invar alloy and Fe72Pt28 alloy under high pressures as a recent application of nano-polycrystalline diamond (NPD)...

Both micro-paired and conical support type double-stage diamond anvil cells (ds-DAC) were tested using a newly synthesized ultra-fine nano-polycrystalline diamond (NPD). Well-focused X-ray sub-micr...

In this study, atomic-scale origin of the Invar effect, which is nearly-zero thermal expansion observed in the Invar alloy ${\mathrm{Fe}}_{65}{\mathrm{Ni}}_{35}$, was investigated by reverse Monte Carlo analysis using complementary data sets of extended x-ray absorption fine structure and x-ray diffraction. The interatomic distances of the nearest neighboring Fe-Fe atomic pairs were $\ensuremath{\sim}0.02$ \AA{} longer than those of the Fe-Ni and Ni-Ni pairs at the minimum pressure in this study (0.6 GPa). The elongation in the Fe-Fe pairs was suppressed with increasing pressure, and the distances of the three pairs were comparable under pressures above the magnetic transition from ferromagnetic to paramagnetic phase at ${P}_{\text{c}}\ensuremath{\approx}7$ GPa. Therefore, the Fe-Fe pairs dominantly contribute to the volume expansion due to the magnetovolume effect. Because a similar magnitude of elongation was observed in the Fe-Fe pairs of a non-Invar Fe-Ni alloy, we conclude that the Invar effect originates from the delicate balance between the number of Fe-Fe pairs and their elongation depending on the magnetization.

The $\ensuremath{\alpha}$ (bcc) phase of single-crystalline iron was compressed along the ${[111]}_{\ensuremath{\alpha}}$ direction under quasihydrostatic and nonhydrostatic conditions. The emergence of the $\ensuremath{\epsilon}$ (hcp) phase variants via the pressure-induced martensitic transformation was investigated using x-ray diffraction and optical observations of the sample surface. In quasihydrostatic compression, the $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\epsilon}$ transition occurred at approximately 14 GPa accompanied by the sudden appearance of texture structures on the mirror-polished sample surface. The texture structure divided the sample surface into two characteristic regions: distorted regions with undulations and flat regions without undulations. Although martensitic transformation based on the Burgers model allows for the emergence of 12 $\ensuremath{\epsilon}$ variants from one single-crystalline phase, the transition proceeded according to the Burgers model, but selected variants preferably emerged depending on the regions in the texture structure. The flat region consisted of only three variants whose $c$ axes were parallel to the sample surface. The region near the undulation exhibited a large number of variants whose $c$ axes aligned parallel and nonparallel to the sample surface. The $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\epsilon}$ transition under nonhydrostatic compression deviated from the Burgers model, and the variant selection was not observed. This study demonstrates that the quasihydrostatic compression along ${[111]}_{\ensuremath{\alpha}}$ reduces the number of variants via strong variant selection. The strong preferred orientation is useful for investigating the anisotropy of physical properties in the $\ensuremath{\epsilon}$ phase.

We have measured the X-ray absorption spectra (XAS), electrical resistivity and magnetic susceptibility of EuRh2Si2, which undergoes a valence transition under high pressures. A sharp decrease in the Eu valence determined from the XAS was observed at around 70 K in the temperature dependence at P = 1.2–1.9 GPa. In the temperature dependence of electrical resistivity and magnetic susceptibility, we observed jumps associated with the temperature-induced valence transition under high pressures. The magnetoresistance detected a field-induced valence transition. The results are discussed from the thermodynamic point of view.

We report the results of the X-ray absorption spectroscopy (XAS) on the intermediate valence compound SmB6. The XAS measurements were performed near the nonmagnetic-magnetic phase boundary. Mean Sm valence v Sm was estimated from absorption spectra, and we found that v Sm near the boundary ( P ≥ 10 GPa and T ∼ 12 K ) is far below a trivalent state with magnetic characteristics. Although the result is markedly different from the cases of pressure induced magnetic orders in Yb and Ce compounds, it is likely that the large deviation from the trivalent state seems to be common in some Sm compounds which possess electronic configuration between 4 f 5 and 4 f 6 with multi 4 f electrons.

In strongly correlated electron systems, a fundamental understanding of the quantum critical behavior in the vicinity of a magnetic quantum critical point (QCP) remains one of the important issues for decades. In particular, the unconventional criticality, which cannot be explained by the spin fluctuation theory, has attracted much attention in 4f electron systems, and the role of the valence instability has been discussed both from theoretical and experimental points of view. Here, we present our systematic high pressure study of X-ray absorption spectra on YbNi3Ga9 and EuFe2As2, revealing the characteristic pressure-induced valence crossover and possibly the relevance of the valence instability to the physical properties near the magnetic QCP.

We report a systematic study of Sm valence in the prototypical intermediate valence compound ${\mathrm{SmB}}_{6}$. Sm mean valence ${v}_{\mathrm{Sm}}$ was measured by x-ray absorption spectroscopy as a function of pressure $(1lPl13\phantom{\rule{0.28em}{0ex}}\mathrm{GPa})$ and temperature $(3lTl300\phantom{\rule{0.28em}{0ex}}\mathrm{K})$. Pressure-induced magnetic order was detected above ${P}_{c}=10\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ by resistivity measurements. A shift toward the localized $4f$ state with increasing $P$ and/or $T$ is evident from an increase in ${v}_{\mathrm{Sm}}$. However ${v}_{\mathrm{Sm}}$ at ${P}_{c}$ is anomalously far below 3, which differs from the general case of nonmagnetic-magnetic transition in Yb and Ce compounds. From the $T$ dependence of ${v}_{\mathrm{Sm}}(P,T)$, we found that ${v}_{\mathrm{Sm}}(P,T)$ consists of two different characteristic components: One is associated with low-energy electronic correlations involving Kondo-like behavior, and the other is associated with high-energy valence fluctuations.

The layered hexagonal EuPtP is a rare substance that exhibits two successive valence transitions occurring simultaneously with valence ordering transitions and an antiferromagnetic order. Anticipating that the application of pressure to this sample would induce a new valence-ordered structure and/or a new phenomenon associated with valence fluctuation, we examined the electrical resistivity ρ, the Eu L3-edge x-ray absorption spectroscopy, and the powder x-ray diffraction under high pressure. We found a new valence transition at around P = 2.5 GPa. After the transition, a new valence-ordered structure is realized at the lowest temperature. The valence-ordered structure is inferred to be stacking of (2+: Eu2+ layer, 3+: Eu3+ layer) along the c-axis. Upon further increases in pressure, the valence-ordered structure is suppressed and another valance-ordered phase is realized up to P = 6 GPa. The antiferromagnetic order collapses in the pressure range between 6 GPa and 8 GPa.

X-ray absorption spectra at the Ti K-edge of a SrTiO

To understand how the constituent atoms participate in the hydrogenation of Pd-based alloys at $\ensuremath{\sim}0.1$ MPa of hydrogen pressure $({P}_{{\mathrm{H}}_{2}})$, we investigated the electronic states in Pd-$M$ $(M=\text{Ru},\text{Rh},\text{Ag},\text{and Au})$ alloys and their hydrides element-selectively by using x-ray absorption spectroscopy at the ${L}_{2,3}$ edges. Spectral changes near the absorption edge demonstrate that both Pd and $M$ atoms form bonds with H atoms in the Pd-$M$ $(M=\text{Ru} \text{and Rh})$ alloys even at ${P}_{{\mathrm{H}}_{2}}\ensuremath{\sim}0.1$ MPa. This is a striking result because high pressures of more than 1 GPa are required for the hydrogenation of Rh and Ru pure metals. In contrast, only Pd atoms bond with H atoms and the $M$-H bond is absent in the case of Pd-$M$ $(M=\text{Ag} \text{and Au})$ alloys. Therefore, the hydrogen-induced changes in the electronic states differ between $M\mathrm{s}$ with fully occupied $d$ shells and $M\mathrm{s}$ with partially occupied $d$ shells. This study reveals that the thermodynamic hydrogenation properties of Pd-$M$ alloys can be determined by a combination of the formation of the $M$-H bond and lattice expansion or compression by alloying Pd metal with $M$.

We have revealed the pressure-induced collapse of the guest Eu off-centering in type-I clathrate Eu8Ga16Ge30 by the measurements of extended X-ray absorption fine structure (EXAFS) at the Ge K-edge...

X-ray absorption spectra under uniaxial pressure were measured at the Ti K-edge of a SrTiO3 single crystal in order to obtain direct evidence for the ferroelectric transition that is expected on the basis of second harmonic generation studies. A uniaxial pressure was applied perpendicular to the ab-plane. The pre-edge peak, which corresponds to Ti 3d e g -O 2pσ bonding, shows little change across the transition temperature of 40 K at 1 GPa. This indicates that a local electric dipole moment is not induced under uniaxial pressure, as opposed to the macroscopic ferroelectric moments that are predicted to be induced along the ab-plane.

We report a novel pressure-driven spin crossover in layered cobalt oxyfluoride Sr2CoO3F with a distorted CoO5 square pyramid loosely bound with a fluoride ion. Upon increasing pressure, the spin state of the Co(III) cation gradually changes from a high spin state (S = 2) to a low spin state (S = 0) accompanied by a anomalously large volume contraction (bulk modulus, 76.8(5) GPa). The spin state change occurs on the CoO5 pyramid in a wide pressure range, but the concomitant gradual shrinkage of the Co–F bond length with pressure gives rise to a polyhedral transformation to the CoO5F octahedron without a structural phase transition, leading to the full conversion to the LS state at 12 GPa. The present results provide new effective strategy to fine-tune electronic properties of mixed anion systems by controlling the covalency in metal-ligand bonds under pressure.

Nano-polycrystalline diamond has been used to obtain a glitch-free X-ray absorption spectrum under high pressure. The advantage and capability of nano-polycrystalline diamond anvils is discussed by a comparison of the glitch map with that of single-crystal diamond anvils., Nano-polycrystalline diamond (NPD) [Irifune et al. (2003 ▶), Nature (London), 421, 599] has been used to obtain a glitch-free X-ray absorption spectrum under high pressure. In the case of conventional single-crystal diamond (SCD) anvils, glitches owing to Bragg diffraction from the anvils are superimposed on X-ray absorption spectra. The glitch has long been a serious problem for high-pressure research activities using X-ray spectroscopy because of the difficulties of its complete removal. It is demonstrated that NPD is one of the best candidate materials to overcome this problem. Here a glitch-free absorption spectrum using the NPD anvils over a wide energy range is shown. The advantage and capability of NPD anvils is discussed by a comparison of the glitch map with that of SCD anvils.

The structural and electronic properties of BiCoO(3) under high pressure have been investigated. Synchrotron X-ray and neutron powder diffraction studies show that the structure changes from a polar PbTiO(3) type to a centrosymmetric GdFeO(3) type above 3 GPa with a large volume decrease of 13% at room temperature revealing a spin-state change. The first-order transition is accompanied by a drop of electrical resistivity. Structural results show that Co(3+) is present in the low spin state at high pressures, but X-ray emission spectra suggest that the intermediate spin state is present. The pressure-temperature phase diagram of BiCoO(3) has been constructed enabling the transition temperature at ambient pressure to be estimated as 800-900 K.

An X-ray magnetic circular dichroism experiment under multiple extreme conditions, 2

We observed the spatially resolved X-ray absorption fine structure of meteoritic inclusion by photoelectron emission microscopy in conjunction with hard-X-ray synchrotron radiation. The cracked domain in the inclusion is identified as Cr 2 FeO 4 (chromite), and its electronic structure shows identical behavior with that of synthetic chromite. The photon energy is also scanned over the extended region to obtain the radial distribution function. It finally shows almost identical behavior as synthetic chromite.

X-ray magnetic circular dichroism (XMCD) is a powerful tool for studying the electronic and magnetic states in ferromagnetic materials. Beamline 39XU at SPring-8 has currently developed the material science using XMCD under high pressures. Here, we briefly review the experimental techniques and the recent outcome of the pressure-dependent XMCD in ferromagnetic Fe, Co, and Ni metals and itinerant ferromagnetic Mn3GaC. The extension to the experiment under multiple extreme conditions, i.e. low temperature, high magnetic field, and high pressure, is also prospected.

The local structures around Co and Fe in ${\mathrm{BiCo}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{3}$ (BCFO) have been determined element-selectively by means of extended x-ray absorption fine structure (EXAFS) measurements at the Co and Fe $K$ edges. In the tetragonal (T) phase at $x\ensuremath{\le}0.63$, both Fe and Co ions are trivalent and locate in the ${\mathrm{O}}_{5}$ pyramidal coordination. The four in-plane Fe bonds with transverse oxygen (Fe-O2) split into $2\ifmmode\times\else\texttimes\fi{}2$ bonds in the monoclinic (M) phase at $0.63\ensuremath{\le}x\ensuremath{\le}0.73$ whereas the Co-O2 bonds do not show a split exceeding the resolution of our EXAFS analysis. This result is an element-specific interpretation of the polarization rotation in the M phase around the morphotropic phase boundary. The components of thermal vibration and static disorder are evaluated separately from the temperature dependence of the Debye Waller factor from $T=8\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ to 300 K. The static disorder of the Fe site is large compared to that of the Co site, thereby indicating that Fe is unstable in the ${\mathrm{O}}_{5}$ pyramidal coordination of the T and M phases. This study demonstrates that the instability of Fe ions plays an important role in the sequential structural distortion of the BCFO system.

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence ${\mathrm{YbNi}}_{3}{\mathrm{Ga}}_{9}$ under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below ${P}_{c}\ensuremath{\sim}9\text{ }\text{ }\mathrm{GPa}$ where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

We demonstrate a new use for photoelectron emission microscopy (PEEM) in combination with hard X-ray synchrotron radiation. With this technique, an X-ray absorption fine structure spectrum can be acquired on each pixel in the observed image, thereby enabling analysis of the electronic properties in nanometer scale. Here, we report the local chemical composition and electronic structure of the Widmanstatten pattern in the Gibeon iron meteorite and clarify that the α lamella exhibits bcc structure with a spatially homogeneous Fe concentration. [DOI: 10.1380/ejssnt.2006.490]

Pressure effects of the magnetic phase transition in DyCo 2 were studied by XRD and XMCD. The magnetic transition changes from 1st order to 2nd order in a range of 4–5 GPa. The Co K -edge XMCD is insensitive to the pressure, which is interpreted as resulting mainly from the pressure variation of Dy 4f magnetic polarization.

The equations of state of CeCu2Si2 and CeCu2Ge2 to about 60 GPa, as well as that of CeNi2Ge2 to 22 GPa and the valence state of Ce in CeCu2Ge2 to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr2Si2-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi2Ge2 at ∼5 GPa and CeCu2Ge2 at ∼7 GPa, respectively, approached that of CeCu2Si2 taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu2Si2, 125.6±4.3 GPa for CeCu2Ge2, and 178.4±14.3 GPa for CeNi2Ge2. The valence state of Ce in CeCu2Ge2 remained trivalent throughout the pressure range investigated.

An experimental system for X-ray magnetic diffraction (XMD) under extreme conditions was constructed on the beamline BL39XU at SPring-8. This system aims at studying magnetic properties of ferromagnets through the measurements of magnetic form factors under the conditions of low temperature (5 K), high magnetic field (6 T) and high pressure (10 GPa). This system consists of a superconducting magnet (SCM), a diamond anvil cell (DAC), a two-axis manipulator for the DAC, a five-axis goniometer for the SCM, and an X-ray polarizer with a phase plate. Details of this system are presented. Experimental results on uranium telluride are shown as a performance test with this instrumentation.

Direct observation of aqueous fluids coexisting with MgSiO 3 (enstatite) and/or Mg2SiO4 (forsterite) was performed at 0.5–5.8 GPa and 800–1000 °C with an externally heated diamond-anvil cell and synchrotron X-rays. At 1000 °C in the MgSiO3 –H2O system, forsterite crystallizes below 3 GPa but not above that pressure. At 1000 °C in the Mg2SiO4 –H2O system, forsterite congruently dissolves into the aqueous fluids up to 5 GPa. These observations suggest that the aqueous fluids coexisting with enstatite and forsterite have Mg/Si < 1 below 3 GPa and 1 < Mg/Si < 2 above that pressure. Comparison with the previous studies reporting Mg/Si ratios of the aqueous fluid coexisting with enstatite and forsterite indicates that the Mg/Si ratios change rapidly from SiO2-rich to MgO-rich at around 3 GPa and 1000 °C. This change can be related to possible structural changes of liquid water under these conditions. The aqueous fluids coexisting with enstatite and forsterite do have Mg/Si ratios similar to those found in the partial melts of H2O-saturated peridotite. Somewhere within the upper mantle, these two fluids unite to form a single regime and cannot be distinguished from each other.

In order to study the magnetic phase transition in Mn3ZnC at 233 K, X-ray magnetic circular dichroism (XMCD) has been measured at the Mn K-edge as a function of temperature and magnetic field. When the transition appears, the spectral intensity shows an abrupt increase with decreasing temperature and a linear reduction with increasing magnetic field. The present results provide evidence that orbital angular momentum is closely associated with the appearance of non-collinear magnetic structure due to the phase transition.

The purpose of this study was to accurately determine the valency of Yb at high pressure and room temperature and to clarify the relation between the valence state and the crystal structure of Yb metal. LIII-edge X-ray absorption near-edge structure (XANES) spectra were measured to determine the valence state of Yb metal in the pressure range from 0 to 34.6 GPa at room temperature, using a diamond anvil cell (DAC) and synchrotron radiation at SPring-8. In the fcc phase, Yb metal exhibits mixed valence (the mean valence v >2.1 ). At the fcc-to-bcc phase transition, a 0.1 jump is found in v . In the bcc phase, v (P) is an increasing function of pressure with downward curvature, reaching only 2.55 at 26 GPa. The v is only 2.65 in the hcp phase at 34.6 GPa. A tendency for saturation in v (P) to values smaller than 3.0 is found.

X-ray magnetic circular dichroism (XMCD) of γ'-iron nitride (Fe 4 N) was recorded at Fe K -edge under high pressue up to 27 GPa. The XMCD intensity decreased remarkably with pressure, and vanished at 24 GPa. Compressibility was measured by the X-ray diffraction method. These results indicate that Fe 4 N undergoes a second-order phase transition from the ferromagnetic state to a paramagnetic state without any structural change. The pressure-induced demagnetizing process is discussed in terms of the Fe magnetic states in the local environment.

By use of synchrotron radiation the powder X-ray diffraction of lanthanide monoarsenides LaAs and LuAs with a NaCl-type structure has been studied up to 60 GPa at room temperature. First-order phase transitions with the crystallographic change were found at around 20 GPa for LaAs, and 57 GPa for LuAs. The high-pressure form of LaAs is a tetragonal structure and can be viewed as a distorted CsCl-type structure. The atoms in the tetragonal structure are located at La: 0, 0, 0; As: 1/2, 1/2, 1/2. The space group is P4/mmm. The structural change to the tetragonal structure occurs with the volume collapse of about 10%. The structure of these high-pressure phases of LuAs is unknown. The volume vs. pressure curves for LaAs and LuAs are fitted by a Birch equation of state. The bulk moduli of both arsenides are 92±6 GPa for LaAs and 85±3 GPa for LuAs. The high-pressure structural behavior of LaX (X=P, As and Sb) and LnAs (Ln=lanthanide) with the NaCl-type structure is discussed.

Ce unoccupied 5d electronic states of the nonmagnetic heavy-fermion compound CeRu 2 Si 2 have been investigated by means of x-ray magnetic circular dichroism (XMCD) experiments. We measure the magnetic field dependences of the CeL 2,3 -edge XMCD of a powder sample with a transmission mode at about 2 K. The magnetic field dependence of the L 2 -edge x-ray absorption spectrum shows a slight enhancement of the white line with metamagnetic behaviour, indicating reduction of the c-f hybridization. The L 2 XMCD spectrum shows a single positive lobe, while the L 3 XMCD spectrum consists of a main negative peak and two small negative satellite peaks. The main structure of CeRu 2 Si 2 is similar to that of CeRu 2 Ge 2 .

By use of synchrotron radiation, powder X-ray diffraction studies for cerium and praseodymium monopnictides [CeX and PrX (X=P, As, Sb and Bi)] with the NaCl-type structure have been carried out up to 40 GPa at room temperature. We have investigated in detail the pressure (P) vs. cell volume (V) relationship for CeP, CeAs and CeSb. The phase transition from the NaCl-type (B1) to the CsCl-type (B2) structure is observed at around 25 GPa for CeP and 21 GPa for CeAs. The transition pressures of both compounds are about 6 GPa higher than the results previously reported. Sevan et al. have predicted that a second isostructural B2–B2 transition for CeSb occurs at around 25.2 GPa with a volume collapse of 4%. However, we cannot find the volume collapse for CeSb at least up to 35 GPa. First-order phase transitions with the crystallographic change for PrX (X=P, As and Sb) are found at 26 GPa for PrP, 27 GPa for PrAs, 13 GPa for PrSb. The structure of the high-pressure phase of these compounds is tetragonal (distorted CsCl-type, P4/mmm). For PrBi, anomalous behavior in the X-ray diffraction pattern is observed around 4 GPa. This may be due to a pressure-induced intermediate phase. The structural phase transition in PrBi occurs at about 14 GPa. The high-pressure phases of PrBi consists of coexisting of tetragonal (distorted CsCl-type, P4/mmm) and cubic (CsCl-type, Pm3m) modifications at about 14 GPa. The bulk modulus of CeX and PrX (X=P, As, Sb and Bi) is obtained from the P–V curve fitted by the Birch equation of state. The relationship between bulk modulus and cell volume for these compounds is studied.

By use of synchrotron radiation, powder X-ray diffraction of ScSb and YSb with a NaCl-type structure has been studied up to 45 GPa at room temperature. A first-order phase transition from the NaCl-type (B1) to a CsCl-type structure (B2) began to occur at around 28 GPa for ScSb and at around 26 GPa for YSb. Crystal data of the high-pressure phase of both antimonides are obtained. The high-pressure structural behavior of ScSb and YSb is similar to that of heavier LnSb (Ln=Dy–Lu). The B1–B2 transition for ScSb and YSb can be understood according to the rigid sphere model. The bulk moduli of ScSb and YSb are about 58 GPa at ambient pressure.

The physical properties relating to 4f electrons in cerium phosphide, especially the temperature dependence and the isomorphous transition that occurs at around 10 GPa, were studied by means of x-ray powder diffraction and charge density distribution maps derived by the maximum-entropy method. The compressibility of CeP was exactly determined using a helium pressure medium and the anomaly that indicated the isomorphous transition was observed in the compressibility. We also discuss the anisotropic charge density distribution of Ce ions and its temperature dependence.

Magnetization-versus-applied-field curves M(H) are calculated for an [Fe(3.48 nm)/Gd(5.43 nm)]15 multilayer film using the Gd magnetization depth profiles derived from the resonant x-ray magnetic scattering data collected with an applied field of 2.4 kOe. Stable magnetic structures for other field strengths are calculated by minimizing the sum of the Fe-Fe, Gd-Gd and Gd-Fe exchange energies and the Zeeman energy in a temperature range of 140-240 K. The calculated curves fit very well the slowly rising M(H) curves observed at temperatures between 140 and 200 K, where the Gd layers are ferromagnetic, over a wide field range up to 50 kOe on adjusting a molecular-field constant for the Fe-Gd interfaces, the only one free parameter used. The concave magnetization depth profiles in the Gd layers are essential to reproduce the observed M(H) curves. The discrepancies between the observed and calculated curves in low-field regions represent the limitation of the single-magnetic-domain model used in the calculation.

Low-temperature magnetic structures of an [Fe/Gd]15 multilayer are determined using the resonant X-ray magnetic scattering technique at a synchrotron source. The difference intensities of specular Bragg reflections observed by flipping the helicity of circularly polarized probing X-rays of energy close to the L3 absorption edge of Gd show that the multilayer is in the Gd-aligned state with the magnetic moments of the Gd layers oriented parallel to the applied in-plane field at H=0.5 kOe, T=10 K. This transforms into the twisted state with canted Gd moments by raising field strength H and/or temperature T. In the twisted state, the Gd moments at the interfaces and the core of the Gd layers show distinctive canting angles. Temperature and field-dependent in-plane rotations of local Gd moments have been visualized.

The effect of Fe-site substitution on structural and physical properties of the infinite layer iron oxide SrFeO2 was investigated under high pressure by 57Fe Mossbauer spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, X-ray magnetic circular dichroism, and electrical resistance measurements using a diamond-anvil cell. Both 20% Mn- and Co-substituted samples exhibit spin transitions from a high-spin (S = 2) to an intermediate-spin (S = 1) state at Pc ∼ 32 GPa, which is much the same pressure 33 GPa observed in SrFeO2. This result indicates that the spin transition pressure is insensitive to the d-orbital electron counts [Mn2+ (d5), Fe2+ (d6), Co2+ (d7)], but is governed by the local structure around the Fe site.

X-ray absorption spectra at the Ti K-edge of a SrTiO3 single crystal under uniaxial pressure were measured to obtain evidence of uniaxial pressure-induced polarization predicted in SrTiO3 from the electronic viewpoint. The pre-edge 3d-e g peak decreases in intensity with increasing uniaxial pressure, together with an energy shift to higher energy side. Contrary to uniaxial deformation, these changes were independent of incident x-ray polarization. This implies the presence of a mechanism that maintains the isotropic coordination environment around a Ti atom, i.e. a tilt and rotation of the TiO6 octahedron accompanied by its isotropic shrinkage, hence the local polarization essential to the ferroelectric order cannot be observed.

We have carried out the high-pressure measurement of X-ray absorption spectroscopy on the intermediate valence compound SmB6 which shows magnetic ordering as well as an insulator-metal transition at critical pressure Pc ~ 10 GPa. The valence of Sm atom at room temperature increases with increasing pressure, however it is far below a trivalent state at Pc . In contrast to cases of pressure-induced nonmagnetic-magnetic transition in Yb compounds, which mostly occurs in the scheme of well localized 4f electrons, the present observation suggests that electronic system in SmB6 still possesses strong delocalized characters at Pc .

We have carefully investigated the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ transition pathway of iron under quasihydrostatic pressures. For this purpose, combined measurements of extended x-ray absorption fine structure (EXAFS) and x-ray magnetic circular dichroism at the Fe $K$ edge were performed using a helium pressure-transmitting medium. Collapse of the ferromagnetism simultaneously occurs with the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ structural transition, which is in contrast to the scenario that the transition is driven by the pressure-induced instability of the ferromagnetism in $\ensuremath{\alpha}$ phase of iron. We conclude that shear stress is important to initiate the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ transition. Our model to fit the EXAFS profile demonstrates that the local atomic arrangement in $\ensuremath{\epsilon}$ phase is slightly distorted due to unfinished shuffle motion, whereas shear motion finishes at the beginning of the transition.