Sintering properties and homogeneity of Ca2+-doped .65Y2O3-.35YCr0.5Mn0.5O3 NTC ceramics

Ceramics suitable for use over a wide temperature and having a negative temperature coefficient (NTC) based on .65Y(2)O(3)-.35YCr(0.5)Mn(0.5)O(3)-doped with CaO were prepared by applying a solid-state reaction at different temperatures (1500-1650 degrees C). The physical properties and scanning electron microscopy results revealed that dense NTC ceramics could be obtained by sintering at >1550 degrees C. The effect of two different sintering methods on the properties of the NTC ceramics was studied, and the results indicated that the NTC ceramics obtained by employing the two-step sintering method exhibited better properties. The contents of Cr and Mn oxides in the NTC ceramic discs prepared by applying two-step sintering (1600 degrees C) exhibited a decreasing trend from inside to outside. To quantify the diffusion rate, Fick's second law was used, and the diffusion coefficients of Cr and Mn oxides in the NTC ceramics were found to be 5.20 x 10(-5) and 2.36 x 10(-5) cm(2)/s, respectively. Resistivity and temperature analyses indicated that the resistivity (rho(25)), B-25/100, and B-700/1000 of the NTC ceramics were 1.61 x 10(6) omega cm, 2367 K, and 2697 K, respectively, which are suitable for a wide temperature range.