CRYSTALLOGRAPHIC STRUCTURES AND PHASE-TRANSFORMATIONS IN ZRPD

Phase transformations and crystal structures in the equiatomic compoun d ZrPd were examined using in-situ heating and cooling in a transmissi on electron microscope (selected-area diffraction and high resolution imaging) and Rietveld refinement of high resolution neutron powder dif fraction data. Three phases were characterized: a high temperature cub ic B2-type phase (Pm3m; Z = 1; a = 0.335 97(3) nm at 800 degrees C); a n orthorhombic CrB-type phase formed by martensitic transformation fro m the B2 phase (Cmcm; Z = 4; a = 0.333 19(3) nm, b = 1.0301(1) nm and c = 0.441 11(4) nm at 400 degrees C) and a monoclinic variant of the C rB-type phase at room temperature (assumed space group Cm; Z = 8; a = 0.66611(6) nm, b =0.87499(7) nm, c = 0.542 35(6) nm; beta = 108.21(1)d egrees). The monoclinic reversible arrow orthorhombic phase transforma tion was found to occur reversibly around 200 degrees C.