N. A. Bendeliani

Phase transition and compressibility of LaF3 under pressures up to 40 GPa

Abstract The compressibility of LaF 3 (tysonite) has been studied up to 40 GPa using X-ray diffraction in a diamond anvil cell. A phase transition from tysonite to an orthorhombic phase ( Cmma , No. 67) was observed at a pressure of 19 GPa at room temperature. The volume discontinuity was Δ V / V 0 =−0.077 at the transition point. The cell parameters of the high-pressure phase are a =8.221(6) A, b =8.589(9) A, c =5.231(6) A, Z =8 at p =16 GPa, which is accepted conventionally as equilibrium. The bulk moduli and pressure derivatives calculated by fitting V ( p ) data to the Birch–Murnagan equation of state are presented for both phases.

Crystal growth at high pressure and the problem of characterization of the interstitial phases in the B–C–O system

Abstract Different crystal growth methods were used to obtain single crystals of interstitial phases based on the α-boron structure in the B–O and B–C–O systems at pressures of 3–7 GPa and temperatures of 1500–2000 K. Boron suboxide carbide B(C,O)0.16 crystals with sizes up to 250 μm, suitable for complete structure analysis, were prepared by chemical reaction between B4C and B2O3 (molar ratio 1:1). The hexagonal unit cell parameters of the B(C,O)0.16 compound are: a=5.618(1) A, c=12.122(1) A, c/a=2.158, Z=38.54 and space group R 3 m. The analytical method for estimation of the chemical composition and the number of atoms per unit cell is presented for this kind of compound.

High-Pressure Phase Transitions of LaF3and CeF3

AbstractThe effect of high pressure on the structure of LaF3 (tysonite), CeF3, and nonstoichiometric LaF3-based solid solutions (rhombohedral system, P

Crystal growth of the high-pressure phase of Mg2Sn

\overline 3

Growth of single crystals of the high-pressure ɛ-FeOOH phase

c1, Z = 6) is discussed. In the systems MF2–LaF3 with M = Pb and Sr, fluorite-like M1 –xLaxF2 + x solid solutions (Fm3m, Z = 4) are obtained in the composition range 0.5 ≤ x ≤ 0.75 by quenching from 1500–1700 K at p = 10 GPa. By extrapolating the composition dependences of the lattice parameter for these cubic solid solutions, the lattice parameter of cubic LaF3 is estimated at a= 5.86 ± 0.02 Å. High-pressure x-ray diffraction studies indicate that CeF3 undergoes a first-order phase transition similar to that revealed recently in LaF3. At p = 20.6 GPa, the lattice parameters of orthorhombic CeF3 (Cmma, Z= 8) are a = 8.062 ± 0.006 Å, b = 8.457 ± 0.009 Å, and c = 5.091 ± 0.006 Å. The transition is accompanied by a 7.3% decrease in volume. The high-pressures structure of LaF3 and CeF3 can be thought of as a distorted modification of the structure of a hypothetical fluorite-like trifluoride. The lattice parameters of the orthorhombic and cubic cells are related by aortho ∼ bortho ∼

Growth of single crystals of the high-pressure phase of α-PbO2

\sqrt 2