Lin-Gun Liu

Compression of Ag and phase transformation of NaCl

The isothermal compression of silver up to 309 kbar has been measured at 23±3°C by high‐pressure x‐ray diffraction employing a diamond‐anvil cell. The B1 phase of NaCl mixed with the silver was used both as a pressure transmitting medium and as an internal pressure calibrant. The data fitted to two forms of the Birch equation yield K0=1180±50 kbar, K0′=3.8±0.5, and K0=1105±95 kbar, K0′=4.6±0.8. When the pressure exceeded 300 kbar, the NaCl underwent a phase transformation to the B2 phase. Increasing the load did not result in the complete disappearance of the B1 phase up to a pressure of 311 and 334 kbar based on the extrapolation of the Ag and Re compression data, respectively. The average volume change measured for the B1‐B2 transformation is −0.83±0.11 cm3/mole, which is 17% smaller than the value reported by Bassett et al. This smaller volume change improves the agreement of NaCl with the linear relationship between volume change and entropy change proposed by Bassett et al. for the B1‐B2 transformati...

EFFECT OF PRESSURE AND TEMPERATURE ON THE LATTICE PARAMETERS OF RHENIUM.

Abstract The effect of pressure on the lattice parameters, hence the molar volume, of the hexagonal close-packed phase of rhenium (Re) was determined at room temperature up to 350 kbar by means of X-ray diffraction employing a diamond-anvil high-pressure cell. The initial bulk modulus of rhenium calculated from the volume data is 3.50 ± 0.15 Mbar. The crystallographic axis ratio, c a , is virtually independent of pressure. No phase transformation was observed within the pressure range studied. The mean coefficients of linear thermal expansion were determined to be (7.03 ± 0.10) × 10−6°C−1 for the a-axis and (4.96 ± 0.07) × 106°C−1 for the c-axis in a temperature range of 12–428°C at a pressure of 1 bar by means of the X-ray diffraction method.

Lutetium: High pressure polymorph and compression

Abstract The effect of pressure on the lattice parameters of the h.c.p. phase of Lu has been studied up to 230 kbar at 23 ± 3°C by means of X-ray diffraction employing a diamond-anvil cell. The data fitted to the Birch equation yield an isothermal bulk modulus of 460 ± 20 kbar with a pressure derivative of 2.8 ± 0.5. The axial ratio ( c a ) decreases nonlinearly with increasing pressure, the decrease being 2.4 per cent at 230 kbar. When the pressure exceeds 230 kbar, Lu transforms reversibly from the h.c.p. phase to the Sm-type structure. The transition occurs with increasing pressure in the range of 230 ± 5 kbar. The lattice parameters of the Sm-type structure at about 231 kbar are a = 3.176 ± 0.006 A and c = 21.77 ± 0.04 A, and the volume change is −0.21 cm 3 mole or −1.6 per cent of the volume of the h.c.p. phase.

High-Pressure Polymorph of Thulium: An X-ray Diffraction Study.

An x-ray diffractiotn study of thulium at room temperature and high pressure by means of a diamond-anvil press has shown that thulium transforms from a hexagonal close-packed structure to the samarium type, as other rareearth elements (gadolinium, terbium, dysprosium, and holmium) do. Unlike the other rare-earth elements, thulium (hexagonal close-packed) has an axial ratio (c/a) that is independent of pressure within experimental error and the transition is reversible. The transition occurs with increasing pressure in the range of 60 to 116 kilobars. The lattice paralieters of the samarium-type phase of thulium at about 116 kilobars are a = 3.327 � 0.005 angstroms and c = 23.48 � 0.04 angstroms, and the volume change at the transition is estimated to be - 0.5 percent of the volume of the hexagonal close-packed phase at the transition.