High-temperature X-ray Powder Diffraction Data Research Articles

Structure refinement and thermal properties of novel cubic borate Lu2Ba3B6O15

Abstract Novel borate Lu2Ba3B6O15 was prepared using a multi-step high-temperature solid-state synthesis. It crystallizes in the cubic system, Ia 3 ¯ space group, a = 14.18197(3) A, V = 2852.396(18) A3, Z = 8, and it is isostructural with Y2Ba3B6O15. The crystal structure is described as a framework composed of the edge-sharing large irregular BaO9 polyhedra. The intersecting tunnels in this framework are filled with the lutetium atoms. Two planar BO3 triangles are connected to each other by the vertices, forming the isolated B2O5 pyroborate groups. The Lu2Ba3B6O15 thermal behavior was investigated by thermal analysis and high-temperature X-ray powder diffraction (HTXRD). The Lu2Ba3B6O15 sample starts to melt at 1058 °C. As the temperature increases, the coefficient of linear expansion increases (αa = 5.7 at 25 °C and 8.9 × 10−6 C−1 at 800 °C). The Rietveld refinement of the HTXRD data showed that thermal deformations of the non-rigid BaO9 polyhedra have the greatest influence on the Lu2Ba3B6O15 expansion among those of the other constituent polyhedra.

Crystal structure and thermal properties of the LixNa1–xKZnP2O7 solid solutions and its relation to the MM′ZnP2O7 diphosphate family

New solid solutions of LixNa1–xKZnP2O7, belonging to the MM’ZnP2O7 structural family (M = Li+, Na+, Zn2+; M’ = Na+, K+), were prepared and phase equilibria along the LiKZnP2O7–NaKZnP2O7 section were reported. These solid solutions were investigated single-crystal X-ray diffraction, high-temperature X-ray powder diffraction (HTXRD), differential scanning calorimetry, and impedance spectroscopy. A miscibility gap was found within the range of 0.8 < x < 1.0, and a binodal curve was constructed using HTXRD data. The similarity of the thermal and compositional deformation of LixNa1–xKZnP2O7 solid solutions is revealed: increasing the radius of the metal by 0.01 Å leads to the same deformations of the crystal structure as increasing the temperature by 31 °C. The Li/Na↔Zn cation exchange lead to an increase in conductivity above 300 °C. The alkali mixed effect in activation energy occurs for LixNa1–xKZnP2O7 solid solutions near x = 0.5. The phase with the 2a×2b×c superstructure ordering was observed as a result of the solid solution melting.

Structure and high-temperature properties of the (Sr,Ca,Y)(Co, Mn)O3−y perovskites — perspective cathode materials for IT-SOFC

Oxygen deficient perovskites Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75, were prepared by using the citrate route at 1373–1573K for 48h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=2×aper, b=2×aper, c=2×aper (a0b−b− tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤x≤0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573K for 48h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4)Å, Rp=0.057, Rwp=0.056, χ2=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298–1073K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1−xMnxO3−y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8ppmK−1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3−y and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1−xMnxO3−y, x=0.5 and 0.75 increases with the temperature reaching 110S/cm for x=0.5 and 44S/cm for x=0.75 at 1173K. Samples of Sr0.75−xCaxY0.25Co0.25Mn0.75O3−y, 0.1≤y≤0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the σ value from ∼1 to ∼50S/cm as the temperature increases from 300 to 1173K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (Ep) increasing from 340 to 430meV with an increase of the calcium content from x=0 to x=0.6.

Structural characterisation of the Ce 1−xLa xNbO 4+δ solid solution series: In-situ high-temperature powder diffraction studies

High-resolution neutron powder diffraction has been utilised to investigate the effect of lanthanum substitution on the structure of cerium niobate, CeNbO 4+ δ , as a function of temperature. Two members of the Ce 1− x La x NbO 4+ δ solid solution series, Ce 0.8La 0.2NbO 4+ δ and Ce 0.2La 0.8NbO 4+ δ , were examined over a temperature range of 293–923 K under a positive pressure of O 2 (500 mbar). From this data it was found that on increasing lanthanum substitution there was an associated reduction in the temperature of the monoclinic-to-tetragonal phase transition. The data also suggested that increasing lanthanum substitution caused an associated decrease in the excess oxygen content. In addition, high-temperature X-ray powder diffraction data recorded in static air were also examined for four compositions of the Ce 1− x La x NbO 4+ δ series ( x=0.2, 0.4, 0.6 and 0.8). These data corroborated the results of the neutron diffraction experiments and also suggested that there was formation of an intermediate phase, analogous to the CeNbO 4.08 phase of the parent material, during the phase transitions of the x=0.8 and 0.6 compositions.

Atomic displacements in the normal-incommensurate phase transition in Co-åkermanite (Ca2CoSi2O7)

New in-situ high-temperature X-ray powder diffraction data on the normal-incommensurate phase transition in Co-akermanite (Ca2CoSi2O7) are presented. Evidence for the phase transition is found in the abrupt change in the thermal expansivity of the c lattice parameter at 220° C. In addition, the c lattice parameter exhibits premonitory effects of the phase transition through the leveling out of the thermal expansivity at temperatures from 87 to 220° C.

Thermal expansion of hydroxyapatite-β-tricalcium phosphate ceramics

The thermal lattice expansion of calcined hydroxyapatite and β-tricalcium phosphate single-phase powder was investigated by high-temperature X-ray diffractometry. The thermal expansion of densely sintered hydroxyapatite-β-tricalcium phosphate composite ceramics was examined by thermomechanical analysis. Hydroxyapatite-β-tricalcium phosphate mixtures with a Ca/P atomic ratio varying from 1.50 to 1.67 were precipitated from Ca(OH) 2 and H 3PO 4 solution at room temperature. The powder, calcined in air at 800°C for 3 h, was pressed in a mould at 98 MPa. The pressed powder pellets were sintered in air at 1150°C for 1 h. High-temperature X-ray powder diffraction data were measured in the temperature range from 25 °C to 1150 °C and calibrated by a platinum internal standard technique. Thermo- mechanical analysis was carried out with a 0.08 kPa compressive load in the range from 25 °C to 1250° C with an α-Al 2O 3 polycrystalline standard. The hydroxyapatite and β-tricalcium phosphate are characterised by non-linear thermal expansion between 25 ° C and 600° C because of HPO 4 2− condensation and dehydration. In the upper temperature region, the hydroxyapatite c-axial dimension expanded sharply from 1000° C to 1150° C owing to the formation of oxyapatite. The c-axial dimension of β-tricalcium phosphate shrank from 850 to 950° C which was ascribed to the formation of an intermediate phase between the β- and α-tricalcium phosphate phases. The mean (25–1000 °C) thermal expansion coefficient of the densely sintered hydroxyapatite-β-tricalcium phosphate ceramics increased almost linearly with an increase in β-tricalcium phosphate content.

Structural changes within the plastic phase of diamantane

Structural changes within the pre-melting plastic phase of diamantane have been revealed from high-temperature X-ray powder diffraction data. A gradual transition to a more disordered state is suggested, and hexagonal symmetry ( a = 14.1 A ̊ , c = 11.0 A ̊ ) for the plastic phase is firmly established.