SYNTHESIS AND PROPERTIES OF COMPLEX OXIDES, LN(2)MN(2 3)TA(4/3)O(7) PHASES (LN EQUALS RARE-EARTH OR Y)/

The complex oxides with a pyrochlore-related structure, Ln(2)Mn(2/3)Ta (4/3)O(7), have been synthesized by the usual ceramic method in a redu cing atmosphere at 1523 K. The X-ray diffraction patterns of these com pounds can be indexed by a hexagonal symmetry. The lattice parameters of the hexagonal crystal are linearly dependent on the ionic radii of Ln(3+). The chemical stability range of Ln(2)Mn(2/3)Ta(4/3)O(7) phases was determined by the isothermal thermogravimetric analysis at 1273 K . The temperature dependence of the magnetic susceptibility of Eu2Mn2/ 3Ta4/3O7 obeys the Curie-Weiss law in the temperature range above 77 K , and the valence numbers of rare earth, manganese and tantalum are 3( +), 2(+) and 5(+) respectively. The results of electrical conductivity exhibit a semiconducting property in the measured temperature range.