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Under strong gravitational fields, the unique uniaxially distorted crystalline state induces structural changes in compounds other than those caused by high pressure and high temperature. We subjected the hexagonal YMnO3 single crystal to a strong-gravitational field (0.78 × 106 G, 400 °C) and determined the changes in the crystalline structure and physical properties of the recovered metastable sample. According to four-circle single-crystal X-ray diffraction data, the structural analyses indicated changes in the inequivalent nearest-neighbor Mn-Mn and Mn-O bond distances, thereby demonstrating that trimerization distortion occurred in the ab plane under the strong gravitational field. Magnetic measurements indicated that there were changes in the magnetic anisotropy, which were explained by changes in the spin–orbit interaction due to lattice distortion.

The local coordination environments of Ti in Cretaceous–Paleogene (K–Pg) from Stevns Klint and Devonian–Carboniferous (D–C) boundary from western part of Cat Co Beach on Cat Ba Island sediments are studied by K-edge X-ray absorption fine structure (XAFS) in order to provide local atomic information by X-ray absorption near edge structure (XANES) and coordination environments by extended X-ray absorption fine structure (EXAFS). Ti K-edge XAFS spectra in bulk part of K–Pg and D–C boundary sediments are compared with those of reference materials such as TiO2 (rutile, anatase and brookite polymorph), CaTiO3, MgTiO3, SrTiO3, PbTiO3, moldavite-brownish, moldavite-green, suevite from Ries crater, impactite, obsidian and Kilauea volcanic glass. The shapes of XANES and EXAFS spectra in K–Pg sediments are similar to those in suevite. Suevite was formed under meteorite impact and its glass component was formed under high temperature and high pressure. Similarities of XANES and EXAFS between K–Pg sediments and suevite indicate that formation process of K–Pg sediments is related to a meteorite impact event. On the other hand, the shape of XANES spectrum in D–C sediments is similar to those in anatase and obsidian. However, the shape of EXAFS spectra in D–C sediments is similar to those in obsidian, rather than anatase. Coordination environments of Ti in D–C sediments suggest that the original glass-like local environments were changed to anatase-like local environments by devitrification. This leads to the conclusion that the analysis of the atomic coordination environments of Ti in boundary sediments can in principle be used as a marker of large meteorite impact, though this Ti local environmental information is actually lost due to the devitrification phenomenon to anatase by quenching process or long-time diagenesis. This may be compensated by the XAFS analysis of Zr because local coordination environments of Zr in same analytical point of K–Pg sediments were not affected by diagenesis (Tobase et al., J Miner Petrol Sci 110:88–91, 2015a).

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.

Iron meteorites record the evolutionary and cosmochemical processes of their parent bodies. Fe–Ni phases in iron meteorites show complex textures from various thermal histories of parent bodies as well as the phase relationships and crystal chemistry of Fe–Ni metal. Synchrotron radiation-based X-ray absorption fine structure spectra and X-ray diffraction were applied herein to the study of iron meteorite NWA 859 Fe, Ni, and Ge contents at the K-edge, since they are effective techniques in identifying crystal structures in iron meteorites. The bond distances of Fe and Ni in tetrataenite and kamacite were detected. Field-emission scanning electron microscopy and energy-dispersive spectroscopy were used to observe the petrological and chemical characteristics of the main minerals, kamacite and tetrataenite, and the trace mineral schreibersite. The tetrataenite phase and body-centered cubic kamacite formed a Widmanstatten pattern and cloudy zone. The extended X-ray absorption fine structure (EXAFS) analyses of NWA 859 and a single-crystal diffraction of tetrataenite show that it has a near-face-centered cubic (FCC) tetragonal structure with 12 nearest-neighboring Ni, Fe, and Ge atoms at distances of rNi-(Ni, Fe) = 2.5170(13) A, rFe-(Ni, Fe) = 2.534(3) A, and rGe-(Ni, Fe) = 2.524(5) A, respectively. Moreover, the X-ray absorption near-edge structure (XANES) spectra suggest that the Ge in tetrataenite exhibits a specific local structure with coordination number 12, suggesting that a new local structure of Ge-(Ni, Fe) was first discovered in extraterrestrial material, forming a stable tetragonal structure at approximately 688–618 K. X-ray absorption fine structure (XAFS) is an efficient technique that could provide us further information about local atomic structures and forming conditions in extraterrestrial materials without damage.

We report the preparation of single-crystal rutile (TiO2) with a unique structure prepared by ultracentrifugation at high temperature (strong gravitational field). Single-crystal rutile was subjected along the c-axis direction to a gravitational field of 0.4 × 106 G at 400 °C, and the uniquely structured single-crystal rutile, which did not conform to Pauling’s third rule, was quenched at ambient conditions. The anisotropy (a/c ratio) of the tetragonal phase increased by 2%. The (Ti–Oa)/(Ti–Ob) and Os/Ou ratios increased by 1.6% and 3%, respectively, and approached 1; Ti–Oa and Ti–Ob are the two Ti–O interatomic distances, and Os and Ou are the shared edge Oa–Oa and the unshared edge Oa–Ob, respectively. This means that the TiO6 octahedral group became isotropic. Os was expanded from its normal size, in contradiction to the usual laws, by the strong gravitational force. Such a structural change has not previously been achieved under high-pressure or high-temperature conditions, and may be related to struc...

We report the effect of a strong gravitational field on oriented crystalline perovskite-type manganese oxide La1−x Sr x MnO3 (LSMO). The perovskite-type manganese oxides La1−x Sr x MnO3 (LSMO) have been investigated for giant magnetoresistance (GMR) by controlling the hole-doping level (x). A strong gravitational field can change in crystalline state and the enhancement of usual diffusion. We subjected oriented crystalline La1−x Sr x MnO3 with different grain and grain-boundary (GBs) Sr concentrations to a strong gravitational field and investigated the resulting changes in the A-site cation diffusion and physical properties of the material. Electron probe micro-analysis (EPMA) results showed appearance of the GBs where the Sr concentration was quite high compared with in other GBs. The quantitative analysis at the grain and GBs indicated that cation diffusion was more enhanced than the annealed one. The temperature dependence of the magnetic susceptibility of the gravity samples changed with the Sr concentration in the grains. The temperature dependence of the resistivity curves of the gravity sample showed several abrupt changes, which corresponded to phase transitions at the grains and GBs, which may be caused by composition changes.

We synthesized Pd-Fe series nanoparticles in solid solution using pulsed plasma in liquid with Pd-Fe bulk mixture electrodes. The Pd-Fe atomic percent ratios were 1:3, 1:1, and 3:1, and the particle size was measured to be less than 10 nm by high-resolution transmission electron microscopy (HR-TEM). The nanoparticles showed face-centered cubic structure. The lattice parameter increased with increasing Pd content and followed Vegard&rsquo, s law, and energy-dispersive X-ray spectra were consistent with the ratios of the starting samples, which showed a solid solution state. The solid solution structure and local structure were confirmed by HR-TEM and X-ray absorption fine structure.

International audience; The first step in the structure solution process is the determination of candidate space groups on the basis of the symmetry of the diffraction pattern, in particular through the analysis of the reflection conditions. Sometimes it may happen that the diffraction pattern is indexed in an alternative setting of the space group, in which the reflection conditions appear different. The discrepancy between the observed reflection conditions and those published in the standard setting of space groups may lead the investigator to erroneously assume his sample is less symmetric than it actually is. After discussing a case from the literature where tetragonal samples were incorrectly described as orthorhombic due to an unusual indexing of the diffraction pattern, we present an example in which diffractions from a pyrite sample were indexed in the Pb3 setting of the space group, instead of the standard Pa3 setting, where the large set of strong violations of reflection conditions with respect to those of the standard setting could have been interpreted as a signature of symmetry lowering to P213. The structure being well-known, the real origin of the apparent violation *

The high-pressure phase of SrGeO3 synthesized at 6 GPa and 1223 K adopts the ideal cubic perovskite-type structure. The Ge—O bond is largely covalent, which influences the thermal vibration behavior of the O atom., Single crystals of the SrGeO3 (strontium germanium trioxide) high-pressure phase have been synthesized successfully at 6 GPa and 1223 K. The compound crystallizes with the ideal cubic perovskite-type structure (space group Pm-3m), which consists of a network of corner-linked regular GeO6 octa­hedra (point-group symmetry m-3m), with the larger Sr atoms located at the centers of cavities in the form of SrO12 cubocta­hedra (point-group symmetry m-3m) in the network. The degrees of covalencies included in the Sr—O and the Ge—O bonds calculated from bond valences are 20.4 and 48.9%, respectively. Thus, the Ge—O bond of the GeO6 octa­hedron in the SrGeO3 perovskite has a strong covalency, comparable to those of the Si—O bonds of the SiO4 tetra­hedra in silicates with about 50% covalency. The thermal vibrations of the O atoms in the title compound are remarkably suppressed in the directions of the Ge—O bonds. This anisotropy ranks among the largest observed in stoichiometric cubic perovskites.

Gallium oxynitrides were prepared in the copresence of various amounts of Fe 3+ by ammonia nitridation of oxide precursors. Their crystallinity reduced in a compositional range up to 3 mol% and improved again above 4 mol% with an appearance of a nitride impurity. The product with 2 mol% of Fe 3+ showed the maximum oxygen content of 21 mol% and minimum nitrogen content of 24 mol%. X-ray absorption spectroscopy, Mossbauer and magnetic measurements suggested a small amount of Fe 3 O 4 -like clusters in the oxynitride products. Density-functional calculations supported that the Fe-O-clustered system is more preferable than the statistical distribution of iron in the hexagonal gallium oxynitride structure.

Single crystals of CaIrO3 were grown from a CaCl2 flux at atmospheric pressure and crystallized with the post-perovskite type of structure. The crystal structure is reinvestigated on the basis of single-crystal X-ray diffraction data measured using a high-power X-ray source, and the atomic thermal vibration behavior is discussed in terms of the coordination environments., Single crystals of the title compound, the post-perovskite-type CaIrO3 [calcium iridium(IV) trioxide], have been grown from a CaCl2 flux at atmospheric pressure. The crystal structure consists of an alternate stacking of IrO6 octa­hedral layers and CaO8 hendeca­hedral layers along [010]. Chains formed by edge-sharing of IrO6 octa­hedra (point-group symmetry 2/m..) run along [100] and are inter­connected along [001] by sharing apical O atoms to build up the IrO6 octa­hedral layers. Chains formed by face-sharing of CaO8 hendeca­hedra (point-group symmetry m2m) run along [100] and are inter­connected along [001] by edge-sharing to build up the CaO8 hendeca­hedral layers. The IrO6 octa­hedral layers and CaO8 hendeca­hedral layers are inter­connected by sharing edges. The present structure refinement using a high-power X-ray source confirms the atomic positions determined by Hirai et al. (2009 ▸) [Z. Kristallogr. 224, 345–350], who had revised our previous report [Sugahara et al. (2008 ▸). Am. Mineral. 93, 1148–1152]. However, the displacement ellipsoids of the Ir and Ca atoms based on the present refinement can be approximated as uniaxial ellipsoids elongating along [100], unlike those reported by Hirai et al. (2009 ▸). This suggests that the thermal vibrations of the Ir and Ca atoms are mutually suppressed towards the Ir⋯Ca direction across the shared edge because of the dominant repulsion between the two atoms.

Crystallographic space group and structural parameters of oxide ion conductor La 9.33 (SiO 4 ) 6 O 2 were investigated based on single-crystal X-ray diffraction data at room temperature (296 K). Results of structure refinements with various structure models indicated that the subjected compound has an apatite structure (space group P 6 3 / m ) with no symmetry lowering and site splitting. The structure refinement was converged at R , w R , and S of 0.018, 0.026, and 0.90, respectively, with 41 parameters. Thermal displacements of the oxide ion at the hexagonal channel site (at 0,0,1/4) were extremely large along the c -axis direction. Seven-coordinated cation sites (6 h La site) were basically fully occupied and cation vacancies were found at the nine-coordinated 4 f La site. These results showed good coincidence with the compound's high oxide ion conductivity. Crystallographic data at 296 K: cell dimensions a = 9.714(1) A and c = 7.183(2) A; F (000) = 824; Z = 1; D c = 5.464(2) g cm −3 .

Local structures around germanium in liquid germanate have been investigated by in-situ X-ray absorption measurements up to 9 GPa at 1000°C. Liquid germanate consisting of tetrahedrally coordinated germanium contracts with increasing pressure without significant changes in the local structure up to 2.5 GPa and then shows an abrupt fourfold-sixfold coordination change around 3 GPa. The coordination change is completed below 4 GPa and a high-density liquid consisting of octahedrally coordinated germanium is stable to 9 GPa. GeO6 octahedron in the high-density liquid is more compressible than that in solids, suggesting the possibility of a density inversion between liquid and solid at higher pressure. By considering the analogy of germanates to silicates, these results give some far-reaching implications for the evolution and dynamics of the Earth’s deep interior.

The anharmonic effective pair potentials V(u) = au2/2 + bu3/3! + cu4/4! for I–Cu bond in γ-, β- and α-CuI have been investigated by the EXAFS technique. The EXAFS spectra near the I L3-edge were measured from 73 to 873 K. In the parameter fitting, we have directly carried out the numerical integration of EXAFS function and evaluated the precise anharmonic effective pair potentials. The effective pair potentials do not change appreciably through the phase transitions, though the extent of anharmonicity is larger in α-CuI than in γ- and β-CuI. The superionic conducting α-CuI has a broad interatomic potential which is similar to those in CuBr and CuCl and the displacements of cation and anion correlate strongly with each other in thermal vibration.

In this paper we report single crystal X-ray diffraction study of an oxide-ion-conductor Nd9.33(SiO4)6O2 at 150 K. By detailed examinations of the atomic positions and an electron density distribution, it was clearly shown that Nd9.33(SiO4)6O2 has an apatite structure (space group P63/m) with no symmetry lowering or site-splitting. All oxygens in the hexagonal channel were located at their ideal positions (2a site at 0, 0, ¼) of the apatite structure, while their thermal displacements were highly anisotropic and that in the c-axis direction was more than four-times larger than those in other directions. Cation vacancies were located at the nine-coordinated 4f Nd site. The other Nd site (seven-coordinated 6h site) were basically fully occupied. This full occupation of the 6h Nd site makes potential waves inside the hexagonal channel smooth and transports of oxide-ions in the channel much easier. The distortion of SiO4 tetrahedron was not apparent. Crystallographic data at 150 K: Cell dimensions a = 9.5556(6) Å and c = 7.019(2) Å; F (000) = 852; Z = 1; D c = 5.779(2) g/cm3.

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We have set up an electrical conductivity measurement system under high-pressure and high-temperature conditions with a multi-anvil high-pressure apparatus based on an AC complex impedance method. With this system, we have successfully measured the electrical conductivity of San Carlos olivine under pressure up to 5 GPa. We explain the physical meaning of the activation enthalpies and activation volumes and give values for these data, which will be a great help for understanding the conduction mechanism for olivine.

In order to examine the effect of pressure on the anharmonicity of Au, extended x-ray absorption fine-structure spectra near the Au L3 edge were measured in the temperature range from 300 to 1100 K under pressures up to 14 GPa using large-volume high-pressure devices and synchrotron radiation. The anharmonic effective pair potentials of Au, V (u) = au2 /2! + bu3 /3!, at 0.1 MPa, 6 and 14 GPa have been calculated. The pressure dependence of the thermal expansion coefficients has also been evaluated. The reliability of the anharmonic correction proposed on the basis of the Anderson scale has been discussed.

Using a large-volume high-pressure apparatus, Li2O–4GeO2 glass and pure GeO2 gel have been compressed to 14 GPa at room temperature and their local structural changes have been investigated by an in situ XAFS (x-ray absorption fine-structure) method. On compression of Li2O–4GeO2 glass, the Ge–O distance gradually becomes short below 7 GPa, showing the conventional compression of the GeO4 tetrahedron. Abrupt increase in the Ge–O distance occurs between 8 and 10 GPa, which corresponds to the coordination number (CN) changing from 4 to 6. The CN change is completed at 10 GPa. On decompression, the reverse transition occurs gradually below 10 GPa. In contrast to the case for Li2O–4GeO2 glass, the Ge–O distance in GeO2 gel gradually increases over a pressure range from 2 to 12 GPa, indicating that continuous change in CN occurs. The Ge–O distance at 12 GPa is shorter than that of Li–4GeO2 indicating that the change in CN is not completed even at this pressure. On complete release of pressure, the Ge–O distance reverts to that of the starting gel.

The single-crystal x-ray diffraction method using a diamond anvil cell is an important method for crystal structure determination under high-pressure. The x-ray absorption spectroscopy under high-pressure provides the detailed information on local structure around particular kinds of atoms, even if the crystal structure is unknown. Extended x-ray absorption fine structure (EXAFS) spectroscopy is useful as a probe of vibration dynamics under pressure. An anharmonic effective pair potential can be investigated using the EXAFS technique. The knowledge of the local structure is of primary importance for the understanding of the complicated physical properties of solid solutions. The change of the spin state of the Co4+ ion in the perovskite-type Sr (Co, Mn) O3 solid solution whose magnetic properties varies according to the compositions have been explained based on the local structure analysis.

The anharmonic effective pair potentials V(u)=au2/2+bu3/3!+cu4/4! for the I–Ag bond in β- and α-AgI have been investigated by the EXAFS technique. The EXAFS spectra near the I K-edge were measured from 7 to 800 K. The measurement near the I K-edge has the advantage for the preparation of uniform specimens to precise measurements at high temperatures. In the parameter fitting, we have directly carried out the numerical integration of EXAFS function and evaluated the precise anharmonic effective pair potentials. The phonon energies have been estimated using the potential parameter a by calculating the dynamical matrix. The Gruneisen parameters γG are calculated from the obtained values of a and b as 2.05 and 1.75 for β- and α-AgI, respectively. The extent of anharmonicity is larger in β-AgI than in α-AgI though the effective pair potentials do not change appreciably through the β–α phase transition. The statistical distribution of Ag in α-AgI and superionic conduction mechanism have been discussed based on the effective pair potential and distribution of I–Ag distances. The time spent on a lattice site is greater than the time spent between the potential-energy minima. However, the probability of finding mobile ions at saddle-point position can be regarded as significant and is several percent at higher temperature in the superionic conducting AgI. The superionic conducting α-AgI has a broad interatomic potential which is similar to that of the octahedrally coordinated compounds and strongly correlated displacement in thermal vibration between cation and anion. The strongly correlated displacement can be attributed to covalent bonds which interact locally. Covalency is important to achieve large mean square displacements.

The structure of Sr4Fe6O13is orthorhombic, space groupIba2, with unit cell dimensionsa= 11.278(3) Å,b= 18.953(6) Å,c= 5.546(3) Å,Z= 4. The crystal structure was refined by full-matrix leastsquares toR= 0.010 using 301 reflections measured with an imaging plate using a Weissenberg camera and mono-chromatized synchrotron radiation of wavelength 1.000 Å. The result is essentially the same with the previously reported structure (Yoshiasa, Ueno, Kanamaru, Horiuchi, 1986) but has yielded some details of the structure in which Fe–O bondings are involved. The polyhedral distortions and ionic radii for the five coordinated Fe3+ions in the structure have been discussed in comparison with those of related structures.

Anomalies in the heat capacity curves of AgI have been detected near the temperature of 150 K. Powder X-ray diffraction experiments have been performed in the temperature range 23–299 K. These anomalies were observed for the specimens which experienced the α- to β/γ-phase transition (heated up to 773 K and then quenched to room temperature) but became unobservable in the subsequent heating cycles. The various values (1.5, 13.0 and 4.1 Jmol −1 ) of the enthalpy of transition obtained depend on the thermal history. It can be considered that the anomaly is a transformation from the intermediate (high-pressure) phase to the β/γ phase.

In order to examine the pressure-induced structural change of liquid silver iodide (AgI), high-pressure and high-temperature in situ x-ray absorption fine structure (XAFS) and x-ray diffraction (XRD) studies have been carried out up to 1200 K and 6 GPa. The modifications in the x-ray absorption near edge structure (XANES) spectra and x-ray structure factors, S(Q), with increasing pressure provide evidence for changes in the short-range order of liquid AgI. The I–Ag bond length in liquid AgI increases by compression up to 2 GPa, which proposes that components with higher coordination than fourfold are introduced. The I–Ag bond length decreases monotonically with compression above 2 GPa, indicating that the structural change involving a coordination-number change is completed below 2 GPa and then a high-pressure form of liquid AgI is stabilized. Comparing the I–Ag bond lengths of liquid AgI with those of crystalline phases, we conclude that the high-pressure form of liquid AgI has a rocksalt-like structure with large vacancies.

The phase transformation from β-Ag 3 SI with Pm3m to α-Ag 3 SI with Im3m occurs with an order-disorder transition of anions. This observation was discussed on the base of the local anion ordered structure in α-Ag 3 SI at 519 K. On the β-α transformation, abnormally large lattice expansion of α-Ag 3 SI was observed in a temperature range of 520 K to 590 K. Structure refinements of α-Ag 3 SI were carried out at high temperatures above 590 K and the weighted R values were in a range between 0.027 and 0.041. Structure analysis was also carried out at 153 K on the α-Ag 3 SI crystal which was obtained by quenching to 153 K from 703 K. These structure analyses revealed that Ag ions in α-Ag 3 SI statistically distribute on 8c and 24g sites with Ag occupancies of about 0.07 and 0.10, respectively.

The local structures of the fluorite-type compounds with a composition of Zr 2 Ln 2 O 7 ( Ln = Gd, Dy, Ho, Er and Yb) have been studied by means of EXAFS spectroscopy. The EXAFS results indicate that Ln 3+ ions are essentially 8-coordinated by oxide ions but Zr 4+ ions are 6-coordinated. The distinct difference in coordination number between Zr 4+ and Ln 3+ ions means that the local structures of the fluorite-type Zr 2 Ln 2 O 7 are similar to the pyrochlore-type structure, even though both Zr 4+ and Ln 3+3 ions are located statistically at the cation sites (4a site) in the fluorite-type lattice. The local structure of the fluorite-type solid solution in the system ( 1 − x )ZrO 2 − x YbO 1.5 (0.18≦ x ≦0.50) has been also studied by EXAFS spectroscopy. The result indicates that the coordination numbers of Zr 4+ and Yb 3+ ions are 6 and 8, respectively, in the solid solution in the compositional range 0.18≦ x ≦0.50, and that the oxygen vacancies are located adjacent to Zr 4+ ions.

(Mg 1 − x Fe x ) 1 − δ O ( x = 0.01–0.43) single crystals (~ 8 mm in diameter) were made by a melt-growth method. Electrical conductivity measurements were carried out as functions of temperature and frequency by a complex impedance method under pressure (~ 43 GPa and ~ 673 K and at 0.1 MPa and ~ 1400 K). Our experimental results show a change in charge transport mechanism in the (Mg 1 − x Fe x ) 1 − δ O solid solution at high temperature. The temperature of inflection point of the slope in Arrhenius plots depend greatly on both composition and extrinsic factors of crystals. The low-temperature conduction mechanism in (Mg 1 − x Fe x ) 1 − δ O solid solution is small polaron. Pressure effect of the electric conductivity was observed and the conductivity increased to 0.5 at log scale of S/m with increasing pressure up to 43.4 GPa. The activation energy was decreased linearly with increasing pressure. Chemical composition and homogeneity of specimen rather than pressure greatly influence the electric conductivity. The activation energy of 2.37(4) eV for the (Mg 0.99 Fe 0.01 ) 1 − δ O solid solution might correspond to a migration enthalpy of O ions through thermally formed defects. It is proposed that a possible dominant electrical conduction mechanism in ferropericlase under the lower mantle conditions, at least in the higher temperature region, is super ionic conduction.

International audience; X-ray absorption and photoluminescence were used to investigate the structure of rare-earth tantalum oxynitrides RTa-(O, N) (R = Nd, Gd, Y). Owing to the size of the rare-earth element, the crystal structure tends towards the pyrochlore or defect fluorite-type structure. EXAFS suggested neodymium and yttrium atoms are coordinated either by 6 + 2 or 6 oxygen/nitrogen atoms in the Nd or Y respective oxynitrides although the coordination number of tantalum is six in both compounds. Photoluminescence for 5 at.% doped europium showed the spectra compatible with the point symmetry C3v lower than Oh in fluorite and D3d in pyrochlore structure type for both the Gd and Y tantalum oxynitrides. These measurements supported that their structure types were basically pyrochlore for Nd and Gd tantalum oxynitrides and defect fluorite for Y tantalum oxynitride but they are highly defective.

The thermal behaviour of atoms in β- and α-AgI has been investigated by means of the EXAFS method in the temperature range 73–815 K. The EXAFS data were analyzed using a formula expressed by the cumulant expansion up to fourth-order terms. The experimental results can be explained satisfactorily by the anharmonic model. The position of each peak in the radial structure function around Ag ions observed in both β- and α-AgI is significantly shorter than that of the simulation of a harmonic model, and shifts apparently to a shorter distance with increasing temperature due to the contributions of third-order terms. The third and fourth cumulants are significant even at 73 K. The temperature dependence for the values of cumulants are different between β- and α-AgI.

Raman spectra were measured on the pyrochlore- and fluorite-type Zr2Gd7 (x=0.50) in the system (1−x)ZrO2−xGdO 1.5 and structure refinements were carried out for both structure types with a composition of x=0.43 by means of single crystal X-ray diffraction. Bond distances in the fluorite-type structure with x=0.43 were in good agreement with those calculated from the effective ionic radii, assuming that Gd3+ ion was coordinated by eight oxygens and oxygen vacancies were adjacent to Zr4+ ion. A Raman spectrum of the fluorite-type Zr2Gd2O7 was very similar to that of the pyrochlore-type, and had the line near 220 cm−1 attributed to the pyrochlore-type Gd4O tetrahedra. Coordination states and stability of the pyrochlore- and fluorite-type structures are discussed based on the present results.

The local structure of the fluorite-type compounds in the system (1− x )Bi 2 O 3 · x Gd 2 O 3 (0⩽x⩽0.45) has been studied by EXAFS. The differential XANES spectra near the Bi-L3 edge slightly change with composition, whereas no change was observed in those near the Gd-L3 edge, indicating a slightly different geometry of coordination polyhedra around Bi ions with composition. The Gd-O and Bi-O distances in the fluorite structure measured at room temperature are almost constant with Gd 2 O 3 content in the composition range studied, except slight abrupt decrease of Bi-O distance at about x =0.37. The Bi-O distances at room temperature and 700°C are the same value for the composition x =0.40. The results in this study indicate that the coordination polyhedra of the dopant Gd ions are rather regular than those of Bi ions and introduction of Gd 2 O 3 into Bi 2 O 3 stabilizes the fluorite structure by forming a cluster of Gd polyhedra.

EXAFS studies on CuBr of α, β and γ-phases are made on the basis of the anharmonic vibration model. It is found that the anharmonic vibrations are quite strong, even at 20 K, which is consistent with an investigation by means of infrared spectroscopy. Also obtained is a negative expansion of the Cu-Br distance at a temperature region higher than 300 K.

The Debye-Waller factor of tetrahedrally coordinated binary crystals such as AgI, CuCl, CuBr, CdSe, CdS, and ZnO is studied by the EXAFS spectroscopy and shows a sharp divergent-like curve with increasing Phillips' ionicity.

The local structures of tektites and natural glasses were studied by Zr K-edge XANES and EXAFS in order to provide quantitative data on bonding distances and coordination numbers. The XAFS measurements were performed at the beam line BL-NW10A of the PF-AR in National Laboratory for High Energy Physics (KEK), Tsukuba, Japan. Zr4+ ion in tektite has different kinds of coordination environment. Various natural glasses are formed under different physical conditions. Impact-related glass, fulgurite and volcanic glasses are typical natural glasses. Upon a devastating impact of a giant meteoroid on the Earth, particles of the Earth's surface were melted and catapulted into outer space, where they finally solidified and fell back to the Earth. Tektites should be formed by this series of processes [1]. Tektite has special local structure of Ca[2]. Glass structure is affected by the pressure and temperature conditions during the glass formation and quenching process. This study indicated that different formation process of natural glasses gives different local structure of zirconium ions. The Zr K-edge XANES spectra of tektite have the double post-edge peaks with different heights. The volcanic glasses and other impact-related glasses such as impactite possessed more simple XANES patterns. The average coordination number of Zr4+ in darwin glass, LDG, volcanic glass and tektite are between 6 and 7. The eight-coordinated Zr4+ shows different XAFS pattern in suevite and köfelsite. All tektites are classified in same type. According to EXAFS measurements, Zr-O distances in tektites are 2.198 – 2.215Å and XANES spectra of tektites have similar shape. It indicates that tektites have similar Zr local structure with 7-fold coordination Zr ions. Impact-related glasses are classified to different types. Volcanic glasses are classified to same types. Impact glasses are formed under different geological processes at impact event and are experienced different physical environments.

Kottogite and symplesite are zinc and ferrous arsenate minerals, respectively. These minerals make the Zn3-x,Fex(AsO4)2·8H2O solid-solution and belongs to the vivianite group of minerals with the chemical formula M3(TO4)2·8H2O. The structure of vivianite and symplesite were determined firstly by Mori and Ito, (1950). The structure of kottigite was refined by Hill, (1979). The strucrure of Zn1.63Fe1.37(AsO4)2·8H2O solid-solution crystallize in space group C2/m with a= 10.342(1), b= 13.484(2), c= 4.7756(5), β=105. 306(4), and Z=2. We performed the structure refinements of (Zn,Fe)3(AsO4)2·8H2O solid-solutions, Ojuela mine, Mapimi Durango, Mexico and Kiura mine, Ohita, Japan by RIGAKU single-crystal structure analysis system RAPID. The R and S values are around 0.03 and 1.08. We determined detail atomic coordinate and hydrogen atom positions. The hydrogen bonds were revealed based on hydrogen positions and bond valence caluculations. The octahedral edge-shareing M2O6(H2O)4 dimers and insular MO2(H2O)4 octahedra are linked by AsO4 terahedra. Two H2O group bonds to (Zn,Fe). Four hydrogen atoms are in the normal hydrogen bonds. Hydrogen atom positions have a tunnel structure and there is a path of proton-conduction and we conjecture that proton conductivity has large anisotropy of one direction. The related minerals, such as paradamite, legrandite and warikahnite have tunnel structure similar to vivianite group.

The high-temperature clinoenstatite (HT-CEn) is one of the important MgSiO3 pyroxene polymorph. The single-crystal of C2/c HT-CEn endmember is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 900-19000C [1]. No report that it is produced as single crystal or large domain has been made on the MgSiO3 endmember. The HT-CEn-type modifications are observed in Ca-poor Mg-Fe clinoenstatite and pigeonite and are always found to be unquenchable in rapid cooling. The high pressure and high temperature experiments of MgSiO3 composition were carried out with a Kawai-type multi-anvil apparatus. The samples were quenched by rapidly releasing the oil pressure load and/or by blow out of anvil cell gasket. The space group of C2/c is strictly determined by Rigaku RAPID Weissenberg photographs and synchrotron radiation. Single-crystal X-ray diffraction experiments were performed at ambient conditions using a Rigaku AFC-5 four circle diffractometer. A total of 9383 reflections was measured and averaged in Laue symmetry 2/m to give 766 independent reflections used for the structure refinements. Final reliability factors converged smoothly to R = 0.029. The single-crystal diffraction analysis shows that the unusual bonding distances frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 1750for HT-CEn. The chain angle for HP-CEn is substantially smaller (1350) and the angle for L-CEn turned to the opposite direction at -1600(=2000). The degree of kinking increases by being curved in more than 1800in the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists in the point of the continuity. It is suggested that the reason which can quench structure under ambient conditions is the present HT-CEn single crystal was formed by the isosymmetric phase transition from HP-CEn. HT-CEn type single-crystals cannot be frozen without pressure.

The local structure around Co, Zn and Sr atoms in incommensurately modulated, melilite-type X2T1 T 2 2 O7 (X=Ca and Sr, T1=Mg, Co and Zn, T2=Si) solid-solutions has been investigated by EXAFS analyses. The modulated structure was confirmed in Ca2-xSrxCoSi2O7 solid-solutions with X=0.0 to 0.6 and for both Ca2Mg1-YCoYSi2O7 and Ca2Mg1-YZnYSi2O7 solid-solutions over the whole compositional range at room temperature. The actual bond-distances determined by the EXAFS method for the T1 site (Co-, Zn-O) in the modulated structure are longer than the mean bond-distances obtained from the X-ray diffraction method. This is attributable to the libration of the T1 tetrahedra. In the Ca1-XSrXCoSi2O7 solid-solution both the Sr-O and Co-O distances by the EXAFS method for the X-site increase from Ca end-member to Sr end-member. These increases are respectively 0.8% and 0.6%. This means the local expansions of the tetrahedral sheets and of the XO polyhedra are well matched. In the modulated Ca2Co1-YMgYSi2O7 and Ca2Zn1-YMgYSi2O7 solid-solutions, the actual Co-O and Zn-O distances for the T1-sites are nearly constant in the whole compositional range. The compositional variations of the local structure around the cations in the solid-solution are different for the X and T1 sites. It is concluded that the local geometric restriction for the size of substituted cation in X site is larger than that in T1 site. The dimension of the tetrahedral sheet puts restriction on the size of the cations situated at the interlayer X sites. In other words, the different behavior of the local geometric restriction between the X and T1 sites is an important feature of the melilite structure and is also related to the modulated structure.

CoC(x) nanoparticles encapsulated in carbon shells were synthesized using a pulsed plasma in liquid ethanol. This is the first time that monolithic cubic phase cobalt carbide nanoparticles have been obtained. X-ray diffraction refinement of the nanoparticles showed that the lattice parameter of prepared cubic phase cobalt carbide is larger than that of CoC(x) (44-0962) and cubic phase Co (15-0806 and 01-1259). The x-ray absorption fine structure spectra near the Co K-edge of the synthesized sample indicated differences from commercial metallic cobalt and cobalt oxide samples. High resolution transmission electron microscopy revealed that a thin carbon coating covered the surface of the nanoparticles. These carbon layers might isolate core CoC(x) material from the outside environment, and allow functionalization by carboxyl groups for the further purpose of targeted drug delivery. The obtained CoC(x)@C particles, with a crystallite size of about 10 nm confirmed by the electron microscope, aggregate into 20-40 nm secondary particles in distilled water as shown by dynamic light scattering, and possess high saturation magnetization of about 120 emu g(-1). The sodium 3'-[1-(phenylaminocarbonyl)-3,4-tetrazolium]-bis(4-methoxy-6-nitro)benzene sulfonic acid hydrate assay and defragmentation of deoxyribonucleic acid on MCF-7 cells after incubation with particles indicate relatively low cytotoxicity of CoC(x)@C nanoparticles, compared with micro-sized and nano-sized metallic cobalt particles and commonly used iron oxides. For the small sized CoC(x)@C particles, the release of cobalt ions was checked by a chelation method with ethylenediaminetetraacetic acid solution to be at a very low level compared with other reference materials.

The synthesis of wurtzite-type ZnS nanoparticles by an electric discharge submerged in molten sulfur is reported. Using a pulsed plasma between two zinc electrodes of diameter 5 mm in molten sulfur, we have synthesized high-temperature phase (wurtzite-type) ZnS nanocrystals with an average size of about 20 nm. The refined lattice parameters of the synthesized wurtzite-type ZnS nanoparticles were found to be larger than those of the reported ZnS (JCPDS card no 36-1450). Synthesis of ZnMgS (solid solution of ZnS and MgS) was achieved by using ZnMg alloys as both cathode and anode electrodes. UV-visible absorption spectroscopy analysis showed that the absorption peak of the as-prepared ZnS sample (319 nm) displays a blue-shift compared to the bulk ZnS (335 nm). Photoluminescence spectra of the samples revealed peaks at 340, 397, 423, 455 and 471 nm, which were related to excitonic emission and stoichiometric defects.

Crystal structure of Sr 4 Fe 6 O 13 was studied by means of a single-crystal X-ray diffraction method. The crystal structure is orthorhombic and belongs to one of perovskite-derivatives constructed from Fe 2 O 3 - and Sr 2 Fe 2 O 5 -slabs perpendicular to the b-axis. One third of ferric ions occupies a distorted octahedral site and others locates at two different lattice sites with five oxygen-coordination. In the SrFeO system, Sr 4 Fe 6 O 13 with a chemical composition of Sr 3 -slabs.

The local structure of the AgBr 1−x I x rock-salt type solid-solution (0≤×≤0.4) was investigated by both EXAFS and single crystal X-ray diffraction. The first nearest neighbor distances from Br to Ag, and those from Ag to Br in the solid-solution can be determined from EXAFS method. Because Ag + surrounded by both Br − and I − ions is locally attracted to Br − , which has larger effective negative charge than I − , the Ag-Br distances gradually decrease with AgI content. There are observed systematic changes in both Br K- and Ag K-edge XANES spectra with increasing AgI content in connection with the change of the local structure in the solid-solution. The Br and I ions are distributed at random over the 4( a ) sites of space group Fm3m without forming clusters. Both cation and anion are displaced from the lattice site because the Ag-Br and Ag-I distances in the solid-solution are close, respectively, to the distances in the pure rock-salt type AgBr and a hypothetical rock-salt type AgI. The particular increase in temperature factors by X-ray diffraction results from the static displacements of both cations and anions from the normal octahedral site. A large enhancement of ionic conductivity in AgI rich region will be ascribed to an increase in the concentration of the Frenkel defect caused by changes in local structures in an equilibrium state.

The detailed structure investigations of Zr2Gd2O7 with pyrochlore- and fluorite-type structures have been carried out by X-ray single crystal method at room temperature. The bond distances between cations and oxide ions versus the site population for cations reasonably support that the fluorite phase is made up of the structure with microdomains of the pyrochlore. Sharp fundamental and diffuse superstructure reflections of the pyrochlore are interpreted assuming that anti-phase domain boundaries lie parallel to the &{211} and that domain sizes are not uniform. It should be proposed that the layers composed of the 48f site oxide ions are anti-phase boundaries. The probability density function maps and effective one-particle potentials of the pyrochlore structure reveal that the magnitudes of anharmonic thermal motions for the 48f site oxide ions are large toward the unoccupied 8b site. Compared to the s-pyrochlore phase (with sharp superstructure reflections), the 48f site oxide ions of the d-pyrochlore (with diffuse superstructure reflections) and fluorite phases have larger temperature factors and gentler potential curves. This is due to that the anti-phase domains are coherent each other and that their electron density distributions are the averages of individual domains.

The local structures of the α-AgI type AgI 1− x Br x solid-solution (0⩽×⩽0.4) at 573 K have been determined by EXAFS and XANES analyses. The AgI and AgBr distances in the solid-solution remain constant values of 2.76 A and 2.69 A, respectively. There are little changes in the Br K and Ag K edge XANES spectra in the solid-solution. It is concluded that only tetrahedral sites are occupied at equilibrium in the solid-solution though the α-AgI type structure has several kinds of sites among interstices of the b.c.c. lattice formed by anions. The AgI distance in α-AgI obtained by EXAFS is significantly shorter than that by diffraction experiments, indicating that the average volume of tetrahedra occupied by Ag ions is smaller than that of unoccupied tetrahedra. The effective one-particle potentials (O.P.P.) and the probability-density functions (P.D.F.) Ag and I atoms in α-AgI are calculated. The potentials along the Ag-I bond do not change appreciably through the βα phase transition. The widespread distribution obtained for both atoms in the P.D.F. maps exhibits that the periodicity is substantially disturbed by the large thermal motion of the atoms. The Ag ion can jump to the neighboring site with appreciable probability by the thermal motion, while the I ion is localized on the b.c.c. lattice. The diffusion path of the Ag ions is determined from the P.D.F. maps. The potential barrier along the diffusion path is evaluated to be 0.07 eV from the O.P.P..