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20 citations found for Åsbrink, S.

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Synchrotron X-ray single-crystal diffraction has been used to study the pressure-induced sequence of phase transi­tions in potassium sodium fluoromanganate.

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Owing to a printer's error, the fourth equation given in the Abstract of the paper by Åsbrink, Kihlborg & Malinowski [J. Appl. Cryst. (1988). 21, 960-962] is incorrect. The correct equation is {\bar \beta}_c(0-7.41 GPa) = -3.35 × 10-4 (GPa)-1.

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Acta Cryst. (1984). A40, C143
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High-pressure X-ray diffraction studies have been performed on powder samples of [beta]-Ti3O5 (C2/m) for pressures up to 38.6 GPa using synchrotron radiation and a diamond-anvil cell. The compressibility is highly anisotropic. Thus, the compression [Delta]l/l0 for the maximum pressure investigated is 5.4, 0.8 and 6.7% for the unit-cell axis directions a, b and c, respectively. The anisotropy is reasonable, considering the crystal structure. The bulk modulus B0, determined from the Murnaghan equation, is 173(10) GPa and B'0 is 7(1).

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The structure of V2TiO5 involves a distribution of the two metal species between two crystallographic sites. The sites between the shear planes are occupied solely by vanadium as VIII, while the shear-plane sites are occupied by both metal atom species, vanadium and titanium. An analysis of the metal-oxygen distances could not distinguish between the two reasonable alternatives for the valency distribution, viz VIII/TiIV or VIV/TiIII. By examining the XANES spectra of the title compound at both vanadium and titanium K edges the valency distribution can be confidently assigned as VIII/TiIV. The usefulness of XANES spectroscopy for solving similar problems involving valency ambiguity is evident.

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The experimental results of some measurements, on an equi-inclination type diffractometer, of the effect of multiple diffraction are reported. Thus, the effect on the extinction correction predicted by Zachariasen is demonstrated. A crystal-size effect is also observed, the theoretical basis for which is derived.

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Acta Cryst. (1984). A40, C396
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The unit-cell parameters of MoO3 (space group Pbnm) have been studied as functions of pressure from 0 to 7.41 GPa in a single-crystal experiment involving measurements at 28 different pressure values. A diamond-anvil high-pressure cell mounted on a four-circle X-ray diffractometer was used. The compressibility of this layer structure was found to be very anisotropic. The mean linear compressibilities in the three main directions of the unit cell have the following values: {\bar \beta}a(0-7.41 GPa) = - 3.2 × 10-3 (GPa)-1, {\bar \beta}b(0-0.49 GPa) = - 3.5 × 10-2 (GPa)-1, {\bar \beta}b(1.54-7.41 GPa) = - 1.1 × 10-2 (GPa)-1, and {\bar \beta}c (0-7.41 GPa) = - 3.35 × 10-3 (GPa)-1, where

{\bar \beta}_d = {{2}\over{d_{1} + d_{2}}}{{d_{2} - d_{1}}\over{P_{2} - P_{1}}},

di is the length of a lattice vector d at the hydrostatic pressure Pi. The compressibility in the [010] direction, i.e. normal to the layers, has a non-linear region and is by far the largest one. On the other hand, the compressibility in the [001] direction, which is the direction of the chains of oxygen coordination polyhedra within each layer, is very small.

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The unit-cell parameters of the mixed-valence oxide V3O5 have been studied as functions of pressure from 0.3 up to 7.5 GPa in a single-crystal experiment involving measurements at 21 different pressure values. A diamond-anvil high-pressure (h.p.) cell of new construction [Malinowski (1987). Submitted to J. Appl. Cryst.] mounted on a four-circle X-ray diffractometer was used. At Pt = 6.25(9) GPa a phase transition was observed at room temperature. This is analogous to the semiconductor-metal transition observed at Tt = 428 K and normal pressure, which implies a change in the ordering of the metal-atom valencies. The linear Eulerian strain tensor for the transition has been calculated. The bulk modulus K has been determined for the low-pressure (l.p.) as well as for the h.p. phase: Kl.p.(0.3-5.5 GPa) = 269(3), Kh.p.(6.3-7.5 GPa) = 175(11) GPa. Certain anomalies in the cell-parameter values in a small pressure interval around the phase transition indicate a preparation in the crystal structure for the transition in both the l.p. and the h.p. phase.



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Synchrotron-radiation X-ray diffraction studies of CaF2 at high pressures have been performed on a powder sample up to 45 GPa and on a single-crystal sample up to 9.4 GPa. The bulk modulus of the low-pressure phase was determined to be B0 = 87 (5) GPa. A phase transition was observed at about 9.5 GPa. The transition is accompanied by a volume contraction of 11%. The high-pressure phase is orthorhombic PbCl2 type (space group Pbnm). The sample only partially reverts to the low-pressure phase upon release of pressure.

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A device is described which uses liquid nitrogen to generate a cold or hot gas stream which is blown directly onto the crystal mounted on an X-ray diffractometer. With a specially constructed high-vacuum (< 1.3 × 10-5 Pa) jacketed silica Dewar tube, it can operate between 83 and 1120 K with a stability over long time periods of ± ¼ K below and ± 1 K above ambient temperature. In the latter case the short-time stability is ± ¼ K for hours. It gives an inert atmosphere at elevated temperatures and allows extensive data collection for the accurate determination of crystal structures. The evaporator, the automatic refilling system and the silica Dewar tube are described.

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The lattice parameters of a single-crystal of BaTiO3 have been measured under high hydrostatic pressure up to 5 GPa using a diamond-anvil high-pressure cell of a new design. The lattice becomes cubic at 2.08 (8) GPa and stays cubic at higher pressures. The pressure dependence of the tetragonal-cubic transition temperature is estimated to be -46 K GPa-1.

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