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A SnI4 molecule lowers its symmetry from T d to [Formula: see text] on the liquid-liquid transition. Because it is possible to lower the molecular symmetry without violating the crystalline symmetry, it is worth examining whether the deformation occurs in the crystalline phase field. Extended x-ray absorption fine structure (EXAFS) measurements on the crystalline state were carried out to investigate the change in the environment around a Sn atom at high pressures and temperatures. We could not find clear evidence on the symmetry change of molecules even close to the melting points, where the melting curve becomes abnormally flat against pressure. Indeed, no inconsistency was found when we assumed that the coordination number of a Sn atom remains unchanged in the temperature and pressure range examined. The situation remains true when the system entered the high-pressure crystalline phase on compression. We can propose a consistent scenario as to the structural change on the phase transformation. The incompressibility of a SnI4 molecule could be suitably quantified. The procedure enabled us to conclude the molecule is more than an order of magnitude incompressible than the lattice.

Non-uniform distortion induced by superstructure domains has been observed during the ordering process of an order–disorder transformation in a single decagonal quasicrystal of Al72Ni20Co8. The full width at half maximum (FWHM) of the fundamental reflections increased below the transformation temperature, Tc. At the same time, the integrated intensity of the fundamental reflections varied drastically at Tc. A small hysteresis was also observed in the temperature dependences of both the FWHM and the integrated intensity of the fundamental reflections. Peak broadening of the fundamental reflections is predominantly dependent on |G∥ | below Tc. In addition, the weak dependence of the peak broadening with |G⊥ | is extracted from the observed FWHM of the fundamental reflections. After deconvolution, the FWHM of the fundamental reflections appears to be a linear combination of |G∥ | and |G⊥ |. Coexistence of the non-uniform distortion and of the random phason strain contributes to the ordering process below Tc. The diffuse scattering from atomic short-range order (SRO) was distributed around the ideal positions of the superstructure reflections. The SRO diffuse scattering disappeared completely above Tc + 10 K. In addition, a small hysteresis of the SRO diffuse scattering was found in the temperature cycle.

The similarity in the shape of the melting curve of GeI4 to that of SnI4 suggests that a liquid–liquid transition as observed in liquid SnI4 is also expected to occur in liquid GeI4. Because the slope of the melting curve of GeI4 abruptly changes at around 3 GPa, in situ synchrotron diffraction measurements were conducted to examine closely the structural changes upon compression at around 3 GPa. The reduced radial distribution functions of the high- and low-pressure liquid states of GeI4 share the same feature inherent in the high-pressure (high-density) and low-pressure (low-density) radial distribution functions of liquid SnI4. This feature allows us to introduce local order parameters that we may use to observe the transition. Unlike the transition in liquid SnI4, the transition from the low-pressure to the high-pressure structure seems sluggish. We speculate that the liquid–liquid critical point of GeI4 is no longer a thermodynamically stable state and is slightly located below the melting curve. As a result, the structural change is said to be a crossover rather than a transition. The behavior of the local-order parameters implies a metastable extension of the liquid–liquid phase boundary with a negative slope.

We have investigated the magnetic properties of a single crystal of multiferroic YbFe2O4. Ferrimagnetic ordering of Fe spins is observed at ~250 K. The magnetization measured during field cooling becomes negative below ~10 K owing to the antiparallel coupling between the Fe and Yb sublattices. The magnetization below ~10 K is flipped by changing the applied magnetic field in a positive direction, a property which may be used to the development of magnetic devices. Magnetocaloric measurements show a broad peak of the entropy change, likely owing to a multiple magnetic transition.

B-site mixed bismuth perovskite oxide of Bi(Mg0.5Ti0.5)O3 (BMT) was grown by high-pressure and high-temperature synthesis to achieve a morphotropic phase boundary induced by pressure. Two types of BMT crystal were obtained: one has an orthorhombic structure and the other has a rhombohedral structure. In situ high-pressure and high-temperature X-ray diffraction measurements were performed. It was clarified that the orthorhombic structure is stabilized in the ambient-pressure phase and the rhombohedral structure is stabilized in the high pressure phase. We also performed local structure analysis by atomic pair-distribution function analysis. The similarity of local structures in the orthorhombic and rhombohedral BMT crystals was revealed, and this similarity enables phase transition under pressure.

Pristine aluminum was hydrogenated to form AlH3 at 8.9 GPa and 600 °C. The cyclic formation and decomposition of the hydride were measured by in situ synchrotron X-ray diffraction measurement. AlH3 synthesized under high pressure and temperature was recovered at ambient conditions. The recovered AlH3 was characterized by conventional powder X-ray diffraction measurement and Raman spectroscopy. The results of the characterization were consistent with that obtained for chemically prepared AlH3 and indicated that single phase α-AlH3 was obtained.

We present the in situ high-pressure-high-temperature x-ray diffraction study of the liquid AlCl(3) and ZnCl(2) halogenides having a quasi-molecular network structure in liquid state at normal pressure. These liquids are intermediate between pure covalent and ionic melts. Structural study of these liquid halogenides is indicative of a rapid and strong breakdown of an intermediate-range order in a tetrahedral network of melts for the initial pressure range, 0-2.5 GPa for AlCl(3) and 0-1.8 GPa for ZnCl(2), and points to rather sharp transitions in liquids with the formation of a short-range order structure similar to ionic melt structures around 4 GPa for AlCl(3) and 3 GPa for ZnCl(2). Thus, pseudo-covalent liquid halogenides like AlCl(3) and ZnCl(2) provide testimony to two phenomena under high pressures, namely, a gradual decay of structural correlations in the tetrahedral network of the melt and a sharp transition from molecular-network to ionic structure in liquid on further compression. Such a two-stage structural transformation under pressure is the general feature for a wide class of simple melts, including most of the pseudo-covalent halogenides.

Bulk specimens of Al x Ga1-x N alloys covering a composition range of 0≤x≤1 were synthesized by a solid-phase reaction under high pressure. In situ X-ray diffraction profiles were measured to observe the alloying process, which began at around 800°C under 6.0 GPa. SEM observation and X-ray analysis of the recovered specimen indicated a uniform distribution of Al and Ga and continuous variations of the lattice constants against the composition, which implies that a solid solution of AlN and GaN is formed regardless of atomic composition.