Indium-containing ceramics with negative temperature coefficient characteristics

Different phases of the transition metal oxide system of indium-manganese-n ickel have been studied by means of X-ray diffraction. The electrical prope rties of the spinel phases have been characterized by measurement of the sp ecific resistivity and activation energy indicating a negative temperature coefficient (NTC) material. The replacement of Mn by In in the system Ni-Mn -O results in the formation of single phase spinels with higher specific re sistivities and thermal constant values. In three series with fixed Ni amou nts of 0.30, 0.45 and 0.60 the cubic-to-tetragonal phase transition takes p lace at nearly the same In content of 0.78. Secondary phases like In2O3 and NiO have been found in samples with a Ni content of 0.60 if the total In c oncentration exceeds 1.32. A linear increase of the thermal constant and lo garithmic resistivity for samples with a nickel content of 0.45 and 0.60 as a function of the indium content have been observed. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.