CERAMIC HEATER AND GLOW PLUG HAVING THE SAME

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The present invention relates to a ceramic heater which is capable of preventing an electric conduction defect of a heat-generating resistor from being causedby a supplied current, thus being excellent in voltage endurance, and a glow plug containing the ceramic heater. The ceramic heater 2 contained in the glow plug 1 has an insulative ceramic base material 21 and the heat-generating resistor 22 embedded in the insulative ceramic base material. The heat-generating resistor 22 has, as main components, an electrically conductive compound, silicon nitride and a grain boundary amorphous glass phase. The amount of the rare earth element contained in the heat-generating resistor is less than 2% by volume in terms of its oxide and, further, a molar ratio R = (A/A+B) of the mol number A of the amount of the rare earth element in terms of its oxide to a total of the mol number A and a mol number B, which is the amount of excess oxygen in terms of silicon dioxide, is 0.3 or less. By achieving such a constitution, the heat-generating resistor is capable of preventing electric conduction defects and of being excellent in voltage endurance.