SYNTHESIS, STRUCTURAL AND ELECTRICAL CHARACTERIZATIONS OF PR2-XBAXNIO4+ -DELTA/

Solid solutions of Pr2-xBaxNiO4+/-delta with K2NiF4-type structure wer e prepared in air and characterized by powder X-ray diffraction, Rietv eld refinements, iodometry titrations, and conductivity measurements. The range of the solid solution was 0 less than or equal to x<0.5. The crystal structure changes from orthorhombic (Fmmm) for x less than or equal to 10.1 to pseudo-tetragonal (I4/mmm) for x greater than or equ al to 0.2. The orthorhombic structure of x=0.1 transforms to tetragona l at low temperature. The bond distances obtained from the Rietveld an alyses did not vary significantly with the Ba content except that of N i-O (parallel to the c-axis) which showed an abrupt increase from x=0. 1 to 0.2. The excess oxygen content (delta) decreases from 0.241 to 0. 03 with increasing substituted Ba contents within the solution range. The samples are all semiconductors at the temperature range 4<T<300 K.