FIRST-ORDER AND 2ND-ORDER PHASE-TRANSITIONS IN TERNARY EUROPIUM PHOSPHIDES WITH THCR2SI2-TYPE STRUCTURE

The ThCr2Si2- type compounds EuFe2P2 and EuRu2P2 exhibit as a function of pressure continuous phase transitions which are accompanied by ext remely strong changes of the lattice parameters and particularly of th e P-P distance d(P-P) along the tetragonal c-axis. In the isostructura l integralvalent LaT2P2 compounds similar phase transitions of second (T = Fe) and first order (T = Co) occur as a Function of pressure indi cating that the T element essentially determines the nature of the pha se transition. The different types of phase transitions are explained phenomenologically. (C) 1998 Elsevier Science B.V, All rights reserved .