High-pressure Synchrotron X-ray Powder Research Articles

Pressure induced octahedral tilting distortion in Ba2YTaO6

Herein we communicate the first example of a pressure induced octahedral tilting distortion in a double perovskite phase, which was observed during the structural characterization of Ba2YTaO6 using high-pressure synchrotron X-ray powder diffraction.

High pressure synchrotron x-ray powder diffraction study ofSc2Mo3O12 and Al2W3O12

Synchrotron x-ray powder diffraction was used to studySc2Mo3O12 and Al2W3O12 at high pressure in a DAC. Both compounds adopt the orthorhombicSc2W3O12 structure under ambient conditions and exhibit anisotropicnegative thermal expansion. A phase transition from orthorhombic(Pnca) to monoclinic(P 21/a) symmetrywas observed at ∼0.25 GPa for Sc2Mo3O12 andat ∼0.1 GPa forAl2W3O12 associated with avolume reduction of ∼1.5–2%. A second crystalline to crystalline phase transition was clearly seen only forSc2Mo3O12 (2.5–3.0 GPa). Peak broadening and almost complete amorphization were observed forSc2Mo3O12 at∼8 GPa, and this was not fully reversible on decompression. At 7 GPa, the amorphization ofAl2W3O12 was not as advanced as for the molybdate and on decompressioncrystalline material was recovered. The compressibility of orthorhombicSc2Mo3O12 is highly anisotropic, but it is almost isotropic for both monoclinicSc2Mo3O12 and Al2W3O12. Both compounds show a reduction in their bulk moduli(K0) atthe orthorhombic to monoclinic transition: 32(2) GPa for orthorhombic and 16(1) GPa for monoclinicSc2Mo3O12, and 48 GPa for orthorhombic and 28(1) GPa for monoclinicAl2W3O12.Sc2Mo3O12 displays very similar high pressure behaviour to the previously studiedSc2W3O12.

Synchrotron X-ray powder diffraction and computational investigation of purely siliceous zeolite Y under pressure.

High-pressure synchrotron X-ray powder diffraction measurements of a sample of purely siliceous zeolite Y (faujasite) were carried out up to 8.0 GPa at room temperature using a diamond anvil cell. Measurements using silicone oil as the pressure-transmitting medium show compression of the zeolite followed by a loss of long-range ordering at 2.2 GPa. The experimentally determined bulk modulus, 38(2) GPa, is, within experimental error, identical to that of quartz. When using a methanol:ethanol:water mixture (16:3:1) as the pressure-transmitting medium, two distinct compressibility regions are observed with a dramatic change in the compression mechanism at 4 GPa. Rietveld refinement analysis of the powder patterns provides a detailed description of the underlying chemistry, with sequential pore filling the main response up to 4 GPa and framework distortions at higher pressures.

The equation of state of PbTiO3 up to 37 GPa: a synchrotron x-ray powderdiffraction study

High-pressure synchrotron x-ray powder diffraction patterns were collected usingID09 of ESRF (Grenoble, France) for a powder sample of PbTiO3, placed in adiamond anvil cell. The patterns were collected at room temperature usingnitrogen (up to 37 GPa) and methanol–ethanol solution (up to 7 GPa) aspressure-transmitting media. The bulk moduli were calculated for the first timeusing the Vinet equation of state and they were compared to those of isostructuralcompounds. The trend of the spontaneous polarization as a function of pressureconfirms that the ferroelectric–paraelectric phase transition at 11.2 GPa possessesa second-order character.

High-pressure structures of alpha- and delta-ZrMo2O8.

In situ high-pressure synchrotron X-ray powder diffraction studies of trigonal alpha-ZrMo(2)O(8), zirconium molybdate, have been performed from ambient conditions to 1.9 GPa, over the alpha-delta phase transition at 1.06-1.11 GPa. The monoclinic structure of delta-ZrMo(2)O(8), stable between 1.1 and 2.5 GPa at 298 K, has been solved by direct methods and refined using the Rietveld method. Significant distortions of the ZrO(6) and MoO(4) polyhedral elements are observed for delta-ZrMo(2)O(8), as compared to the ambient conditions of the alpha-phase, while the packing of anions becomes more symmetric at high pressure.

High-pressure properties of TiP2O7, ZrP2O7and ZrV2O7

High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7and ZrV2O7have been performed. The ZrV2O7structure undergoes a reversible transition at 1.38–1.58 GPa from cubic α- to pseudo-tetragonal β-ZrV2O7that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4 GPa, ZrV2O7becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5 GPa, respectively). These differences in high-pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, α-ZrV2O7and β-ZrV2O7were estimated to be 42 (3), 39 (1), 17.0 (7) and 20.8 (10) GPa, respectively.

Compressibility and thermal expansivity of synthetic apatites, Ca5(PO4)3X with X = OH, F and Cl

The room-temperature unit-cell volumes of synthetic hydroxylapatite, Ca 5 (PO 4 ) 3 OH, fluorapatite, Ca 5 (PO 4 ) 3 (F (sub 1-x) ,OH x ) with x = 0.025, and chlorapatite, Ca 5 (PO 4 ) 3 (Cl (sub 0.7) ,OH (sub 0.3) ), have been measured by high-pressure (diamond anvil-cells) synchrotron X-ray powder diffraction to maximum pressures of 19.9 GPa, 18.3 GPa, and 51.9 GPa, respectively. Fits of the data with a second-order Birch-Murnaghan EOS (i.e. (dK/dP) (sub P = O) = 4) yield bulk moduli of Ko = 97.5 (1.8) GPa, K 0 = 97.9 (1.9) GPa and K 0 = 93.1(4.2) GPa, respectively. The room-pressure volume variation with temperature was measured on the same hydroxyl- and fluorapatite synthetic samples using a Huber Guinier camera up to 962 and 907 degrees C, respectively. For hydroxyl- and fluorapatite, the volume data were fitted to a second-order polynomial: V(T)/V 293 = 1+alpha 1 (T-293)+alpha 2 (T-293) 2 with T expressed in K leading to alpha 1 OH = 2.4(+ or -0.1)X10 (super -5) K (super -1) , alpha 2 OH = 2.7(+ or -0.1)X10 (super -8) K (super -2) and alpha 1 F = 3.4(+ or -0.1)X10 (super -5) K (super -1) , alpha 2 F = 1.6(+ or -0.1)X10 (super -8) K (super -2) , respectively. A significant increase is observed in hydroxyl-apatite thermal expansion above ca. 550 degrees C and extra reflections start to clearly appear on the X-ray film above 790 degrees C. These features are interpreted as the progressive dehydration of slightly Ca-deficient hydroxylapatite (i.e. with Ca/P 2 , hydroxylapatite should dehydrate to form gamma -Ca 3 (PO 4 ) 2 +Ca 3 Al 2 Si 3 O 12 below 12 GPa, i.e. below the upper-pressure stability-limit of apatite that was previously determined experimentally.

Image Plate Studies of Tetrahedral Semiconductors Under Pressure: The Implication for Experiment and Theory

A series of high-pressure synchrotron x-ray powder diffraction experiments on tetrahedral semiconductors have been performed using an image plate area detector system in conjunction with a standard diamond anvil cell (DAC). Initial studies have focused on pressure-induced structural transitions in zincblende semiconductors with emphasis on the previously well-studied InSb compound. Site ordering of the nearly isoelectronic constituents is confirmed in some of the high pressure phases for the first time. Structural solutions are proposed which differ in essential features from previously suggested structures. The results obtained are discussed in the context of present theoretical understanding and data from new total energy calculations will be presented. The experimental evidence for phase transition-induced defects will be presented along with complimentary total energy pseudopotential calculations of their formation energies

A high-pressure synchrotron X-ray powder diffraction study of K2SnBr6

Using synchrotron energy-dispersive X-ray powder diffraction (EDXRPD) the authors have shown that K2SnBr6 transforms at pressures of 14 kbar and above from the parent monoclinic cell to a cubic structure of symmetry Fm3m, which is stable to 120 kbar. A different phase appears to exist above 120 kbar.