L. M. Lityagina

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.

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

Single-crystal structures of high-pressure phases FeOOH, FeOOD, and GaOOH

\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

Elastic moduli and the mechanical properties of stishovite single crystals

acubic and cortho ∼ acubic.