OXYGEN DEFICIENCY AND ELECTRICAL-CONDUCTIVITY OF ND(1-X)A(X)NIO(3-Y) (A EQUALS ALKALINE-EARTH) PREPARED BY THE LOW-TEMPERATURE PROCESS

The structure and electrical conductivity of oxygen-deficient Nd(1-x)A xNiO(3-y) (A = alkaline earth) have been investigated. The samples wer e prepared from aqueous solutions of metal acetates and EDTA by the lo w-temperature process. Single-phase NdNiO3-y and alkaline earth-substi tuted Nd(0.95)A(0.05)NiO(3-y) (A = Mg, Ca and Sr) were obtained by hea ting at 700 degrees C for 20 h in flowing oxygen. All the samples had large numbers of oxygen vacancies with y = 0.25-0.28, resulting in the mixed valence state of Ni2+/Ni3+, confirmed by iodometric titration a nd XPS measurements. The lattice constants of the alkaline earth-subst ituted samples were larger than those of the non-substituted sample. T hese results were attributed to the difference in ionic radius. The su bstitution of alkaline earths for Nd decreased the decomposition tempe rature. All the samples showed resistivity on the order of 10(-1) Omeg a cm at room temperature, and the temperature dependence of the electr ical resistance revealed the transition from metallic to semiconductin g at lower temperatures. The transition temperature was dependent on t he substituted alkaline earths. This behavior is discussed in terms of the changes in lattice constants as well as in the valence of Ni resu lting from the oxygen deficiency.