Structure, oxygen deficiency and electrical properties of Nd_1-xY_xNiO_3-y (x = 0, 0.1) prepared by sol-gel method

Perovskite-type NdNiO_3-y and Nd_0.9Y_0.1NiO_3-y were prepared by healing the gel-derived powders at 700 °C in flowing oxygen or in air for relatively short heating time of 20 h, and the lattice constants, oxygen content, valence state of Ni ions and temperature dependence of the electrical resistance were measured. A new oxygen-deficient orthorhombic phase NdNiO_3-y was found, which has larger lattice constants and lower metal-semiconductor (M-S) transition temperature than the previously known NdNiO₃ phase. By substituting Y for Nd in the present NdNiO_3-y, the lattice constants all decreased and the M-S transition temperature increased from 130 to 240 K. The changes in the lattice constants and the M-S transition were discussed in terms of the ionic radius and the electronic bandwidth, respectively.