SYNTHESIS AND PROPERTIES OF A NEW COMPLEX OXIDE DY2MNTA1+XO7+DELTA WITH A PYROCHLORE-RELATED STRUCTURE

A new complex oxide with a pyrochlore-related structure Dy2MnTa1+xO7+delta was synthesized from the oxides Dy2O3 Ta-1+x O-1+delta and Mn2O3 at 1523 K in air. The X-ray diffraction patterns could be assigned to a hexagonal symmetry. The lattice parameters are a = 7.3917 +/- 0.0003 Angstrom and c = 17.1473 +/- 0.0009 Angstrom. It is shown by thermogravimetric analysis that the nonstoichiometric phase of Dy2MnTa1+xO1+delta exists stably over the range of oxygen partial pressure 1 similar to 10(-21) atm at 1273 K. A magnetic measurement shows that the quaternary oxide Dy2MnTa1+xO7+delta has a paramagnetic property and the valence numbers of dysprosium and tantalum are 3(+) and 5(+) respectively, while that of manganese includes 2(+), 3(+) and 4(+) depending on the oxygen nonstoichiometry. Semiconducting property was also observed from the results of electrical conductivity in the measured temperature range.