Pressure dependence of Raman-active phonons in rare earth disulfides, alpha '-LnS(2) (Ln : La, Pr, Nd)

High-pressure behavior of layered alpha'-LnS(2) (Ln: La, Pr, Nd) rare earth disulfides (P2(1)/b, C-2h(5), Z = 4) with the distorted anti-Fe2As structu re (the PbFCl type, P4/nmm, D-4h(7) Z = 2) is studied dth Raman spectroscop y in a diamond anvil cell at room temperature. Upon compression, there occu rs a phase transition in all three compounds to higher symmetry superstruct ures of the parent anti-Fe2As structure. This transformation, associated wi th a hysteresis on decompression, takes place at about 5 GPa for alpha'-LaS 2 and alpha'-PrS2, and at about 8 GPa for alpha'-NdS2. (C) 1999 Elsevier Sc ience B.V. All rights reserved.