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Single crystals of Ir2S3 (diiridium trisulfide) and Rh2S3 (dirhodium trisulfide) were grown in evacuated silica-glass tubes using a chemical transport method and their crystal structures were determined by single-crystal X-ray diffraction analysis. These compounds have a unique sesquisulfide structure in which pairs of face-sharing octahedra are linked into a three-dimensional structure by further edge- and vertex-sharing. Ir2S3 and Rh2S3 had similar unit-cell parameters and bond distances. The atomic displacement parameter (MSD: mean-square displacement) of each atom in Ir2S3 was considerably smaller than that in Rh2S3. The Debye temperatures (ΘD) estimated from the observed MSDs for the Ir, S1 and S2 sites in Ir2S3 were 259, 576 and 546 K, respectively, and those for Rh, S1 and S2 in Rh2S3 were 337, 533 and 530 K, respectively. The bulk Debye temperature for Ir2S3 kashinite (576 K) was found to rank among the higher values reported for many known sulfides. The bulk Debye temperature for Rh2S3 bowieite (533 K) was lower than that for Ir2S3 kashinite, which crystallizes in the early sequences of mineral crystallization differentiation from the primitive magma in the Earth's mantle.

Single crystals of Ni3Se2 (trinickel diselenide) and NiSe (nickel selenide) with stoichiometric chemical compositions were grown in evacuated silica-glass tubes. The chemical compositions of the single crystals of Ni3Se2 and NiSe were determined by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS). The crystal structures of Ni3Se2 [rhombohedral, space group R32, a = 6.02813 (13), c = 7.24883 (16) Å, Z = 3] and NiSe [hexagonal, space group P63/mmc, a = 3.66147 (10), c = 5.35766 (16) Å, Z = 2] were analyzed by single-crystal X-ray diffraction and refined to yield R values of 0.020 and 0.018 for 117 and 85 unique reflections, respectively, with F o > 4σ(F o). R32 is a Sohncke type of space group where enantiomeric structures can exist; the single-domain structure obtained by the refinement was confirmed to be correct by a Flack parameter of −0.05 (2). The existence of Ni—Ni bonds was confirmed in both compounds, in addition to the Ni—Se bonds. The value of the atomic displacement parameter (mean-square displacement) of each atom in NiSe was larger than that in Ni3Se2. The larger amplitude of the atoms in NiSe corresponds to longer Ni—Se and Ni—Ni bond lengths in NiSe than in Ni3Se2. The Debye temperatures, θD, estimated from observed mean-square displacements for Ni and Se in Ni3Se2, were 322 and 298 K, respectively, while those for Ni and Se in NiSe were 246 and 241 K, respectively. The existence of large cavities in the structure and the weak bonding force are likely responsible for the brittle and soft nature of the NiSe crystal.

Single crystals of Ni

The stability of hauerite (MnS2) as compared to that of pyrite (FeS2) can be explained by the long Mn–S distance and departure from the typical pyrite-type structures. The structural differences of MnX2 compounds (X=S, Se, and Te) are the result of spin configurations that are different than those of other MX2 compounds; however, the arrangement of d-electrons and the size of the ions in MnX2 compounds do not clearly explain why Mn2+ in MnX2 does not exist as a low spin state. To investigate the structural differences of MnX2 compounds, we synthesized single-crystal MnTe2 and MnSe2 and performed single-crsytal X-ray diffraction experiments. The single-crystal X-ray diffraction experiments were conducted on MnTe2 [a=6.9513(1) Å, u-parameter=0.38554(2), space group Pa3̅, Z=4], MnSe2 [a=6.4275(2) Å, u-parameter=0.39358(2)], MnS2 [hauerite; a=6.1013(1) Å, u-parameter=0.40105(4), obtained from Osorezan, Aomori, Japan], and FeS2 [pyrite; a=5.4190(1) Å, u-parameter 0.38484(5), obtained from Kawarakoba, Nagasaki, Japan]. The X-ray intensity datasets of these compounds do not show any evidence of symmetry reduction. In MnS2, the S–S distance is 2.0915(8) Å, which is significantly shorter than that of FeS2 (2.1618(9) Å), and the mean square displacement of S (U 11=0.00915(9) Å2) is smaller than that of Mn (U 11=0.01137(9) Å2). The thermal vibration characteristics of MnX2 compounds are significantly different than those of FeS2. Based on structural refinement data, we discuss the low spin state of MnX2 compounds and the structural stability of pyrite-type structures.

Pre-edge peaks in 3d transition-metal element (Sc, Ti, V, Cr and Mn) K-edge XANES (X-ray absorption near-edge structure) spectra in AO2 (A = Ti and V), A 2O3 (A = Sc, Cr and Mn) and AO (A = Mn) are measured at various temperatures. Quantitative comparisons for the XANES spectra were investigated by using absorption intensity invariant point normalization. The energy position of the difference peak (D peak) is obtained from the difference between the low- and high-temperature XANES spectra. There are two kinds of temperature dependence for pre-edge peak intensity: rutile- and anatase-type. The true temperature dependence of a transition to each orbital is obtained from the difference spectrum. In both anatase and rutile, the pre-edge peak positions of A2 and A3 are clearly different from the D1- and D2-peak positions. The A1 peak-top energies in both phases of VO2 differ from the D1 peak-top energies. The D-peak energy position determined by the difference spectrum should represent one of the true energies for the transition to an independent orbital. The peak-top positions for pre-edge peaks in XANES do not always represent the true energy for independent transitions to orbitals because several orbital transitions overlap with similar energies. This work suggests that deformation vibration (bending mode) is effective in determining the temperature dependence for the D-peak intensity.

Single crystals of the vanadate garnet Ca2NaCd2V3O12 (dicalcium sodium dicadmium trivanadate) were synthesized using the floating-zone method and the crystal structure was investigated using single-crystal X-ray diffraction. We considered the effectiveness of substitution of the Y-site cation with reference to previous structural studies of vanadate garnets. The structures of vanadate garnets are subject to geometric constraints similar to those of silicate garnets. These constraints force the tetrahedral–dodecahedral shared edge length in vanadate garnets to become shorter than the unshared dodecahedral edge length, as in ugrandite (uvarovite, grossular and andradite) garnets. However, the vanadate garnet Ca2NaCd2V3O12 exhibits the normal structural feature, similar to pyralspite (pyrope, almandine and spessartine) garnets, namely that the dodecahedral–dodecahedral shared edge length is shorter than the unshared dodecahedral edge length. With increasing ionic radius of the Y-site cation, the atomic coordinates x, y and z of oxygen adopt values which satisfy Pauling's third rule.

Single crystals of pyrite-type PdSb2 were grown by sealing a stoichiometric proportion of the elements in an evacuated silica glass tube and heating the tube in a furnace at 930 K for 20 days. The crystal structure of PdSb2 [space group Pa 3 ¯ , a = 6.4659(2) A, u = 0.37331(3), Z = 4] was refined to R1 = 0.0171 for 374 unique reflections obtained by single-crystal X-ray diffraction experiments. The lattice constant, a, and anion-anion distance of 2.8677(3) A are slightly different from the previously reported values. The single crystal diffraction method has excellent advantages such that the Debye temperature can be determined for each crystallographically independent site. The obtained ΘD values for Pd and Sb in PdSb2 are 258 K and 214 K, respectively. Characteristically, the Debye temperatures, ΘD, of both atoms in PdSb2 were found to be very low among the pyrite-type transition metal pnictides and chalcogenides. Certain regularities between the cation–anion bonding distances and Debye temperatures were found in pyrite-type compounds. The vibration of anion contributes to the highest energy part of the normal mode of thermal vibration, when the cation–anion bonding distances in pyrite-type compounds are shorter than 2.6 A.

The Sr–Ge–O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca–Si–O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr–Ge–O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3perovskite single crystals in the sample recovered in the compression experiment of SrGeO3pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium–oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6octahedra and between GeO6octahedra and GeO4tetrahedra. The present SrGe2O5is thus isostructural with the high-pressure phases of SrSi2O5and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6and GeO4polyhedra to cation substitution at the Sr site are much less than that of the SrO12cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

Dehydration behavior of a natural hydrated Ca-chabazite with composition (Ca1.57Na0.49)(Al3.39Si8.55)O24·12.47H2O has been studied by the structure analyses based on the in-situ high-temperature single-crystal X-ray diffraction data at 100, 200 and 250 °C. Among the five water sites (OW1–OW5) and four exchangeable-cation sites (Ca1–Ca4) found previously in the room-temperature (RT) structure, the present structure analyses revealed the presence of OW1, OW4, Ca3 sites at 100 °C and of OW3, Ca3, Ca4 sites at 200 and 250 °C. The presence of the new extraframework sites was also revealed: OW2’ site at 100 °C and Ca5 site at 200 and 250 °C. From the temperature dependence of the occupation for these extraframework sites, the dehydration and cation migration processes are summarized and rationalized as follows. With heating up to 100 °C, OW3 water molecules, having no bonds to exchangeable cations, are completely desorbed. Simultaneously, Ca1 and Ca2 cations lose the large amounts of water molecules as ligands (OW1 and OW5 for Ca1, OW4 for Ca2); this brings about the simultaneous migration of both cations to adjacent Ca3 site, surrounded by more ligands. With further heating up to 250 °C, OW2’ water molecules, having no bonds to exchangeable cations, are completely desorbed. Simultaneously, most of the Ca3 cations migrate to adjacent Ca4 and Ca5 sites by losing the large amounts of water molecules as ligands (OW1, OW4). A part of the water molecules desorbed in the temperature range of 100–250 °C migrate to OW3 site to be bonded to the remaining Ca3 cations. The peculiar temperature dependence of Si/Al−O1, −O2 and −O3 bond lengths in the framework structure can be explained in terms of their bond-valence variations due to such dehydration and cation migration processes. On the other hand, the variation of Si/Al−O4 bond length is dominated by thermal expansion effect rather than the bond valence effect.

Study of arsenic (As) provides guidelines for the development of next-generation materials. We clarify the unique structure of the third crystalline polymorph of natural As (Pnm21-As) by crystallographical experiment and the electronic structure by first-principles computational method. The crystal structure of Pnm21-As is a novel structure in which the basic portions of semi-metalic grey-As and semi-conductor black-As are alternately arranged at the atomic level. For both covalent and van der Waals bonding, the contributions of sd and pd hybridizations are important. Van der Waals bonding characteristics and d orbital contributions can be varied by control of layer stacking. Total charges are clearly divided into positive and negative in the same elements for the grey-As and black-As portions, respectively, is of importance. The sequence in which one-dimensional electron donor and acceptor portions alternate in the layer will be the first description.

Single-crystal X-ray diffraction study of CaGeO3 perovskite has been conducted over the temperature range of 98 to 1048 K. The crystal begins to deteriorate at a temperature above about 900 K and completely amorphizes by 980 K. The diffraction-intensity distribution and the structure refinements indicate that the Pbnm structure is kept until the occurrence of amorphization. The obtained unit-cell parameters, unit-cell volumes, bond lengths, and displacement parameters increase monotonously with increasing temperature. Thus, no evidence for the existence of the Cmcm high-temperature phase, previously suggested above 520 K, is observed. The Ge-O bond lengths show much smaller thermal expansions than the Ca-O bond lengths; the former ranges between 0.42(2) × 10−5 K−1 and 0.57(2) × 10−5 K−1, and the latter between 1.58(4) × 10−5 K−1 and 3.96(6) × 10−5 K−1. The Debye temperatures and static disorder components for each constituent atom were determined by applying the Debye model to the temperature dependence of mean square displacements (MSDs) of the atoms. Consequently, no significant static disorder components can be detected in each atom. The Debye temperatures averaged over all directions, obtained from the Debye model fitting to U eq, yield the harmonic one particle potential coefficients of 4.76(2) eVA−2 for Ca, 11.0(1) eVA−2 for Ge, 5.02(2) eVA−2 for O1, and 5.33(5) eVA−2 for O2. These values become larger in order of Ca < O1 < O2 << Ge, which shows that the one particle potential of Ge is much narrower than that of Ca. This relationship between Ca and Ge is consistent reasonably with bonding stiffness expected from the thermal expansion coefficients of the bond lengths. The anisotropies of MSDs are remarkable in O1 and O2 atoms as a consequence of the strong interaction with adjacent Ge atoms, forming the rigid bonds with these O atoms. In comparison of the three Pbnm orthorhombic perovskites of CaGeO3, CaTiO3, and MgSiO3, all of these have the BO6 octahedra more rigid than the AO12 polyhedra (A = Ca or Mg; B = Ge, Ti, or Si) and the tilt angles of BO6 octahedra are the largest in MgSiO3 perovskite. These observations indicate that if MgSiO3 perovskite under high pressures undergoes the same sequence of the high-temperature phase transitions as CaTiO3 perovskite, the phase boundaries have positive Clapeyron slopes and the phase transition temperatures should become further much higher than those (1512 K for the Pbnm to I 4/ mcm transition and 1635 K for the I 4/ mcm to Pm 3 m transition) observed in CaTiO3 perovskite at ambient pressure. This leads to the conclusion that the high-temperature phase transition to a perovskite phase with different symmetry under high pressures previously suggested in MgSiO3 perovskite is unlikely.

Single crystals of the vanadate garnet Ca

Pre-edge peaks in 3d transition-metal element (Sc, Ti, V, Cr and Mn) K-edge XANES (X-ray absorption near-edge structure) spectra in AO

The Sr-Ge-O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca-Si-O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO

A high-temperature single-crystal X-ray diffraction study of a synthetic PbTiO3perovskite was carried out over the wide temperature range 298–928 K. A transition from a tetragonal (P4mm) to a cubic (Pm \bar 3 m) phase has been revealed near 753 K. In the non-centrosymmetricP4mmsymmetry group, the difference in relative displacement between Pb and O along thec-axis is much larger than that between Ti and O. The Pb and Ti cations contribute sufficiently to polarization being shifted in the opposite direction compared with the shift of O atoms. Deviation from the linear changes in Debye–Waller factors and bonding distances in the tetragonal phases can be interpreted as a precursor phenomenon before the phase transition. Disturbance of the temperature factorUeqfor O is observed in the vicinity of the transition point, whileUeqvalues for Pb and Ti are continuously changing with increasing temperature. The O site includes the clear configurational disorder in the cubic phase. The polar local positional distortions remain in the cubic phase and are regarded as the cause of the paraelectricity. Estimated values of the Debye temperature ΘDfor Pb and Ti are 154 and 467 K in the tetragonal phase and decrease 22% in the high-temperature phase. Effective potentials for Pb and Ti change significantly and become soft after the phase transition.

Single crystals of the SrGeO3 high-pressure phase are prepared by hot pressing of the polycrystalline pseudowollastonite SrGeO3 (BN anvil press, 6 GPa, 1223 K, 1 h).

Powder samples of Na-GTS have been prepared using a hydrothermal method. Er3+- exchanged Na-GTS [Na4(1-x)Er(4/3)x Ti4Si3O16nH2O] with the compositions in the range of 0.28 ≤ x ≤ 0.64 was obtained by shaking the single-phase sample of Na-GTS in the ErC13 aqueous solutions (25 mL, 0.01~0.1 M) at 25 °C for 6 hours. The chemical analyses by atomic absorption spectrometry (AAS) show that the maximum allowance of Er3+ incorporated into Na-GTS is x = 0.64. TG-DTA measurements show that the incorporation of Er3+ slightly decreases the water contents and the dehydration temperatures. The powder X-ray diffraction (XRD) patterns indicate that the diffraction-peak intensities vary systematically with increasing the Er3+ composition (x). The simulation of XRD patterns suggests the cation-distribution model that Er3+ and Na+ ions preferentially occupy the 4e and 6g sites, respectively.

Single-crystal X-ray diffraction study of SrGeO3 perovskite (cubic; space group Pmɜm) synthesized at 6 GPa and 1223 K was conducted at a low temperature of 100 K. The residual electron density revealed the presence of the bonding electron at the center of the Ge–O bond, in accordance with our previous conclusion that the Ge–O bond is strongly covalent. From comparison with our previous structure-refinement result at 296 K, the mean square displacement (MSD) of the O atom in the direction of the Ge–O bond is suggested to exhibit no significant temperature dependence, in contrast to that in the direction perpendicular to the bond. Thus, the strong covalency of the Ge–O bond can have a large influence on the temperature dependence of thermal vibration of the O atom.

Zr and Ti K-edge XANES spectra of PbZrO3, PbTiO3 and BaTiO3 perovskite-type compounds were measured in the temperature range from 10K to 850K. Quantitative comparisons for the near-edge spectra were performed in a wide temperature range using the absorption intensity invariant point (AIIP) standardization. Clear temperature dependence for pre-edge shoulder is identified by the calculating the temperature difference of the XANES spectrum intensity. Decrease of pre-edge shoulder and peak intensity is observed only in the para- and ferro-electric phases and draw curves, not straight lines. The gradients for shoulder and pre-edge peak intensity are rich in a variety. The decrease in absorption of pre-edge peak and shoulder is speculated due to the shift from the off-centre position of the Zr atom with respect to the oxygen octahedron to center position. The Zr ion in the PbZrO3 para-electric phase has same temperature behaviors of Ti ions in the ferroelectric perovskite.

Ni, Cr, Fe, Ca and Mn K-edge XANES and EXAFS spectra were measured on K-T boundary clays from Stevns Klint in Denmark. According to XANES spectra and EXAFS analyses, the local structures of Ni, Cr and Fe in K-T boundary clays is similar to Ni(OH)2, Cr2O3 and FeOOH, respectively. It is assumed that the Ni, Cr and Fe elements in impact related glasses is changing into stable hydrate and oxide by the weathering and diagenesis at the surface of the Earth. Ca in K-T boundary clays maintains the diopside-like structure. Local structure of Ca in K-T clays seems to keep information on the condition at meteorite impact. Mn has a local structure like MnCO3 with divalent state. It is assumed that the origin on low abundant of Mn in the Fe-group element in K-T clays was the consumption by life activity and the diffusion to other parts.

The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy. The surface of meteorites were melted and volatilized with extreme high temperature and large temperature gradient when meteorites were rushed into atmosphere. This study indicated that meteorite fusion crusts have unique local structures. The local structures of fusion crusts differ from tektites especially in intensity of the shoulder in the rising flank of the edge in Ca XANES spectra. It is consistent with chemical composition change by the volatilization of Si at fusion during atmospheric entry. The high estimated Fe3+/ (Fe2++Fe3+) ratio in meteorite fusion crusts indicates that meteorite fusion crusts are formed into atmospheric oxidation condition. The Ca-O distances in meteorite fusion crusts are 2.612.66 A and are extremely longer than in other natural glasses. The fusion crusts have unique local structure since they experienced extremely high temperature and short quenching time. The XAFS method is effective in distinction of meteorite fusion crusts and classification of natural glass.

A variable-temperature single-crystal X-ray diffraction study of a synthetic BaTiO3perovskite has been performed over the temperature range 298–778 K. A transition from a tetragonal (P4mm) to a cubic (Pm \overline 3 m) phase has been revealed near 413 K. In the non-centrosymmetricP4mmsymmetry group, both Ti and O atoms are displaced along thec-axis in opposite directions with regard to the Ba position fixed at the origin, so that Ti4+and Ba2+cations occupy off-center positions in the TiO6and BaO12polyhedra, respectively. Smooth temperature-dependent changes of the atomic coordinates become discontinuous with the phase transition. Our observations imply that the cations remain off-center even in the high-temperature cubic phase. The temperature dependence of the mean-square displacements of Ti in the cubic phase includes a significant static component which means that Ti atoms are statistically distributed in the off-center positions.

High-temperature powder X-ray diffraction measurements for ScAlMgO4 ( in space group) grown by Czochralski method were carried out from 303 to 1473 K. The obtained temperature-dependent unit cell parameters were expressed as for the a-axis and for the c-axis, where T is temperature in kelvin. The axial thermal expansion coefficients for the a-axis estimated from the unit cell parameters were comparable to those of GaN and ZnO. A c-plane ScAlMgO4 substrate can be easily obtained with using cleavage plane along c-plane, which is parallel to a-axis. Thus, ScAlMgO4 is one of the promising substrates for c-plane epitaxial growth of GaN and ZnO. High temperature X-ray single crystal structural analysis of ScAlMgO4 demonstrated the mechanism of the nonlinear variation of the obtained cell parameters as a function of temperature.