INVESTIGATIONS ON STRUCTURE AND PHYSICAL- PROPERTIES OF SOME NEW MEMBERS OF THE LAPD2O4 FAMILY

The new mixed valent oxopalladates MPd(2)O(4) (M = Pr, Nd, Gd, Y) have been synthesized from the binary oxides in presence of a solid oxygen carrier (KClO3) by applying hydrostatic pressure (ca. 2 GPa). Accordi ng to X-ray investigations these oxides crystallize in space groupe I4 (1)/a (No. 88) and are isotypic to LaPd2O4 (PrPd2O4: a = 5.8382(2), c = 10.1687(5)A; NdPd2O,: a = 5.8419(3), c = 10.1949(6) A; GdPd2O4,: a = 5.7799(3), c = 10.0677(8) A; YPd2,O-4: a = 5.7359(3), c = 9.9829(8) A ). The crystal structure consists of square planar PdO4, units which a re stacked to form columnar arrangements along [100] and [010], respec tively. The PdO4, squares are connected via common corners to a three- dimensional framework. By substitution of Pr3+, Nd3+, Gd3+ and Y3+ for lanthanum the Pd-Pd distances decrease and the electrical conductivit ies increase. The oxopalladates investigated in this work are black, p aramagnetic and semiconducting. At ambient pressure they decompose at temperatures above 880 K into elemental palladium and the binary rare earth oxides.