High-pressure Crystal Structure Research Articles

Erratum: X-Ray Diffraction to 302 Gigapascals: High-Pressure Crystal Structure of Cesium Iodide

In the report "X-ray diffraction to 302 gigapascals: High-pressure crystal structure of cesium iodide" by H. K. Mao et al. (3 Nov., p. 649), reference 10, to a paper by R. Reichlin et al. [ Phys. Rev. Lett. 56, 2858 (1986)], was incorrectly numbered ( 9 ) in the text (p. 649, column 3, line 1; p. 650, column 1, line 49).

ADA Deficiency Treatment

In the report "X-ray diffraction to 302 giga-pascals: High-pressure crystal structure of cesium iodide" by H. K. Mao et al. (3 Nov., p. 649), reference 10, to a paper by R. Reichlin et al. [Phys. Rev. Lett. 56, 2858 (1986)], was incorrectly numbered (9) in the text (p. 649, column 3, line 1; p. 650, column 1, line 49).

X-ray Diffraction to 302 Gigapascals: High-Pressure Crystal Structure of Cesium Iodide

X-ray diffraction measurements have been carried out on cesium iodide (CsI) to 302 gigapascals with a platinum pressure standard. The results indicate that above 200 gigapascals CsI at 300 K has a hexagonal close-packed crystal structure with the ideal c/a ratio of 1.63 +/- 0.01. The crystal structure and pressure-volume relations converge at high pressure with those of solid xenon, which is isoelectronic with CsI. The results indicate a significant loss of ionic bonding in the hexagonal close-packed metallic phase of CsI at ultrahigh pressure.

Bulk moduli and high-pressure phases of the uranium rocksalt structure compounds-I. The monochalcogenides

Abstract The high-pressure crystal structures of the compounds UX, where X = S, Se and Te, have been studied using X-ray diffraction in the pressure range up to about 60 GPa. A rhombohedral distortion is observed for US above 10 GPa. Use and UTe transform to the CsCl structure at about 20 GPa and 9 GPa, respectively. The latter transformations show a considerable hysteresis when releasing the pressure. The scaling behaviour of the bulk modulus has been studied. It is shown that a log-log plot of the bulk modulus versus specific volume for the cubic phases gives a straight line with a slope near - 2.

High-pressure synthesis and crystal structure of VGe 2 and Cr 4Ge 7

The new germanides, Cr 4Ge 7 with the defect disilicide-type structure and VGe 2 with the C40 structure, are synthesized at 4–5.5 GPa and 800–1100°C for 1–3 hr using the belt-type high-pressure apparatus. The relationship between the chemical composition and crystal structure in transition metal disilicides and digermanides is systematically discussed. The following chemical composition sequence accompanied with the change of crystal structure is proposed for the high-pressure synthesis of transition metal ( T) silicide ( X) and germanide ( X) systems: T nX m P T n′X m′, (n > n′ and m n < m′ n′ < 2) P TX 2 .

ChemInform Abstract: High Pressure Synthesis and Crystal Structure of Neodymium(III) Oxide Peroxide, Nd2O2(O2).

AbstractThe title compound has been obtained in pure form by reaction of Nd2O3 and KO2 at 1500 °C and 40 kbar (30 min, slow cooling to 1000 °C, extraction with H2O, no yield given).

High-pressure crystal chemistry of chrysoberyl, Al2BeO4: Insights on the origin of olivine elastic anisotropy

High-pressure crystal structure refinements and axial compressibilities have been determined by x-ray methods for the olivine isomorph chrysoberyl, Al2BeO4. Unlike silicate olivines, which are more than twice as compressible along b than along a, chrysoberyl (space group Pbnm) has nearly isotropic compressibility with β a =1.12±0.04, β b =1.46±0.05, and β c =1.31±0.03 (all×10−4 kbar−1). The resultant bulk modulus is 2.42±0.05 Mbar, with K′ assumed to be 4. The axial compression ratios of chrysoberyl are 1.00:1.30:1.17, compared to axial compression ratios 1.00:2.02:1.60 for forsterite. These differences in compression anisotropy arise from differences in relative bond compressibilities. In chrysoberyl the average aluminum-oxygen and beryllium-oxygen bond compressibilities are similar, yielding nearly isotropic compression, but in silicate olivines octahedral cation-oxygen bonds are significantly more compressible than Si-O bonds, so that compression parallel to a is much more restricted than that parallel to b. The inherent anisotropy of the olivine structure is not, by itself, sufficient to cause anisotropic compression. It appears that in the case of olivine the distribution of cations of different valences, in conjunction with the structure type, leads to anisotropies in physical properties.

High-Pressure crystal chemistry of spinel (MgAl2O4) and magnetite (Fe3O4): Comparisons with silicate spinels

High-pressure crystal structures and compressibilities have been determined by x-ray methods for MgAl2O4 spinel and its isomorph magnetite, Fe3O4. The measured bulk moduli, K, of spinel and magnetite (assuming K′=4) are 1.94±0.06 and 1.86±0.05 Mbar, respectively, in accord with previous ultrasonic determinations. The oxygen u parameter, the only variable atomic position coordinate in the spinel structure (Fd3m, Z=8), decreases with pressure in MgAl2O4, thus indicating that the magnesium tetrahedron is more compressible than the aluminum octahedron. In magnetite the u parameter is unchanged, and both tetrahedron and octahedron display the 1.9 Mbar bulk modulus characteristic of the entire crystal. This behavior contrasts with that of nickel silicate spinel (γ-Ni2SiO4), in which the u parameter increases with pressure because the silicon tetrahedron is relatively incompressible compared to the nickel octahedron.

High-pressure crystal chemistry of phenakite (Be2SiO4) and bertrandite (Be4Si2O7(OH)2)

Compressibilities and high-pressure crystal structures have been determined by X-ray methods at several pressures for phenakite and bertrandite. Phenakite (hexagonal, space group R\(\bar 3\)) has nearly isotropic compressibility with β=1.60±0.03×10−4 kbar−1 and β=1.45±0.07×10−4 kbar−1. The bulk modulus and its pressure derivative, based on a second-order Birch-Murnaghan equation of state, are 2.01±0.08 Mbar and 2±4, respectively. Bertrandite (orthorhombic, space group Cmc21) has anisotropic compression, with β a =3.61±0.08, β b =5.78±0.13 and β c =3.19±0.01 (all ×10−4 kbar−1). The bulk modulus and its pressure derivative are calculated to be 0.70±0.03 Mbar and 5.3±1.5, respectively.

Compressibility of the BeO4 tetrahedra in the crystal structure of phenacite.

The high pressure crystal structure of phenacite Be2SiO4 has been studied based on single-crystal diffraction intensities collected at 22 kbar and 32 kbar. The result has revealed that the Be–O bonds show a large mean coefficient of linear compression 3.2×10−4 kbar−1 ±1.3×10−4 kbar−1 compared with the empirically predicted value 0.824×10−4 kbar−1 for Be–O in general; the Si–O bond lengths are almost invariable in the pressure range covered.

High-pressure crystal structure of quartz up to 102–kbar

High-pressure crystal structure of quartz up to 102–kbar

Bulk moduli and high-pressure crystal structures of rutile-type compounds

Unit-cell parameters and crystal structures of five rutile-type compounds, including TiO 2; SnO 2, GeO 2, RuO 2; and MnF 2;, have been determined at pressures to 50 kbar at 20°C. All five compounds compress anisotropically with the a axis approximately twice as compressible as c. The one variable positional parameter, x of oxygen or fluorine, changes little with pressure. The uniform behavior of these RX 2 compounds at high pressure contrasts with their highly variable structural changes at high-temperature. Rutile-type oxides are, therefore, unlike most oxides and silicates, in which structural variations at high pressure mirror those at high temperature.

Bulk moduli and high-pressure crystal structures of rutile-type : Robert M. Hazen and Larry W. Finger, Geophysical Laboratory, Carneige Institution of Washington, Washington, DC 20008, U.S.A.

Bulk moduli and high-pressure crystal structures of rutile-type : Robert M. Hazen and Larry W. Finger, Geophysical Laboratory, Carneige Institution of Washington, Washington, DC 20008, U.S.A.

90-kilobar diamond-anvil high-pressure cell for use on an automatic diffractometer

A gasketed diamond-anvil high-pressure cell is described which can be used on a four-circle automatic diffractometer to collect x-ray intensity data from single-crystal samples subjected to truly hydrostatic pressures of over 90 kilobars. The force generating system exerts only forces normal to the diamond faces to obtain maximum reliability. A unique design allows exceptionally large open areas for maximum x-ray access and is particularly well suited for highly absorbing materials, as the x rays are not transmitted through the sample. Studies on ruby show that high-pressure crystal structure determinations may be done rapidly, reliably, and routinely with this system.

Pressure dependence of the Davydov splitting in tetracene single crystals

The reflection spectrum of the OO component of the first singlet transition of tetracene single crystal has been measured as a function of pressure in the range 1 atm–6.5 kbar. A discontinuous change in the Davydov splitting occurs near 3 kbar confirming the existence of a pressure-induced first order phase transition discovered recently by measurements of the magnetic field anisotropy in the single crystal tetracene fluorescence. The pressure-induced spectral red-shifts are larger in the low-pressure (LP) phase than those in the high-pressure (HP) crystal structure. The Davydov splitting of the OO band however increases with increasing pressure at a larger rate of 57 cm −1/kbar for the HP phase as compared with 46 cm −1/kbar for the LP phase.

High pressure synthesis and crystal structure of a new series of perovskite-like compounds CMn 7O 12 (C = Na, Ca, Cd, Sr, La, Nd)

A new series of perovskite-like compounds CMn 7O 12 have been synthesized under high pressure and high temperature conditions. C is a large divalent or trivalent cation such as Ca, Cd, Sr, La and Nd. The structures of the quenched materials have been determined from powder X-ray data. They are distortions of the NaMn 7O 12 cubic structure. The [C 2+Mn 3+ 3](Mn 3+ 3Mn 4+)O 12 compounds are trigonal ( R 3 ). The C 2+ and Mn 3+ as well as the Mn 3+ and Mn 4+ cations are ordered on the corresponding A and B sites of the perovskite structure, respectively. The [C 3+Mn 3+ 3] (Mn 3+ 4)O 12 compounds are monoclinic ( I 2 m ). In these compounds the order exists only in the A sites. It is shown that the lower symmetry may be the result of a cooperative Jahn-Teller effect of the Mn 3+ cations occupying the B sites.

High pressure synthesis and crystal structure of NaMn 7O 12

A new compound, NaMn 7O 12, with the perovskite-like arrangement has been synthesized at 80 kbar and 1000°C. This compound is cubic, a = 7.3036 Å, space group Im3 with four formula weights per unit cell. The structure has been solved by Patterson and Fourier synthesis and refined by least-squares based on 142 reflections. The final R and wR factors were 0.025 and 0.033, respectively. The A sites of the perovskite structure are occupied by sodium and manganese atoms in an ordered fashion. The sodium atoms are each surrounded by a 12-oxygen polyhedron whereas the manganese atoms have four nearest oxygens at 1.909 Å forming a square and four more at 2.688 Å forming a rectangle perpendicular to the square. The distortion of the oxygen network from the ideal perovskite structure is similar to that found for In(OH) 3 and Sc(OH) 3.

The high pressure synthesis, crystal structure, and properties of CrP4 and MoP4

The high pressure synthesis, crystal structure, and properties of CrP4 and MoP4

High-Pressure Synthesis and Crystal Structure of α-LiAlO2

First Page