Abstract: A sintered body of zirconia material for an oxygen concentration sensor exhibiting an electromotive force in accordance with the difference in the concentration of oxygen between a gas tested and a reference gas, consisting essentially of partially stabilized sintered zirconia and at least one additive selected from the group of yttrium oxide, calcium oxide and ytterbium oxide which zirconia has a cubic phase and a monoclinic phase existing in mingling relation. The ratio of the X-ray diffraction intensity of the surface (111) of the monoclinic phase to the X-ray diffraction intensity of the surface (111) of the cubic phase or the ratio I(111)/I(111) is in the range between 0.05 and 0.40, and the value of the X-ray diffraction intensity ratio caused by heating the sintered zirconia material to, and holding the same at, the temperature range between 200.degree. and 300.degree. C. minus the former ratio of the X-ray diffraction intensity is in the range between -0.05 and +0.10.

Abstract: Thermistors having a resistor which comprises aluminum oxide (Al.sub.2 O.sub.3) and chromium oxide (Cr.sub.2 O.sub.3) are excellent in heat resistance even when they are used at a high temperature of 400.degree. - 1,100.degree.C. Proportion of Al.sub.2 O.sub.3 and Cr.sub.2 O.sub.3 is preferably 11 mol % of Cr.sub.2 O.sub.3 and 89 mol % - 6 mol % of Al.sub.2 O.sub.3. Furthermore, calcium oxide and silicon oxide may be added to accelerate the sintering of the Al.sub.2 O.sub.3 and Cr.sub.2 O.sub.3. In addition, manganese oxide or titamium oxide may be contained in the resistor for more accurate control of temperature.