Murata Manufacturing Co., Ltd.

Naoaki Abe

Atsushi Kishimoto

Akinori Nakayama

Hayato Katsu

Masato Goto

Tatsuya Matsunaga

A semiconductor ceramic includes a BaTiO-based composition, as a main component, having a perovskite structure represented by general formula ABO, wherein part of Ba constituting the A site is replaced with Na, Bi, Ca, and a rare-earth element having an ionic radius smaller than that of the Na; the content of the rare-earth element when the total number of moles of the elements constituting the A site is 1 mole is 0.0005 to 0.015 on a molar basis; and the content of the Ca when the total number of moles of the elements constituting the A site is 1 mole is 0.05 to 0.20 (preferably 0.125 or more and 0.175 or less) on a molar basis. A PTC thermistor includes a component bodyformed of the semiconductor ceramic. Accordingly, high reliability is achieved even if an alkali metal element is present.

Semiconductor ceramic and positive temperature coefficient thermistor

A semiconductor ceramic includes a BaTiO-based composition, as a main component, having a perovskite structure represented by general formula ABO. The molar ratio m between the A site and the B site satisfies 1.001&#x2266;m&#x2266;1.01. Part of Ba constituting the A site is replaced with Bi, Ca, a rare-earth element, and Na. The molar content of the Ca when the total number of moles of the elements constituting the A site is 1 mole is 0.05 to 0.20 (preferably 0.125 to 0.175). A PTC thermistor includes a component body formed of the semiconductor ceramic. Accordingly, there is provided a lead-free semiconductor ceramic that substantially does not contain lead and that has desired PTC characteristics and high reliability.

A semiconductor ceramic includes a BaTiO-based composition, as a main component, having a perovskite structure represented by general formula ABO. Part of Ba constituting an A site is replaced with at least an alkali metal element, Bi, and a rare-earth element, and the molar ratio m between the A site and a B site is 0.990&#x2266;m&#x2266;0.999 (preferably 0.990&#x2266;m&#x2266;0.995). Preferably, part of the Ba is replaced with Ca, and the content of the Ca when the total number of moles of the elements constituting the A site is 1 mole is 0.042 to 0.20 (preferably 0.125 to 0.175) on a molar basis. A PTC thermistor includes a component body formed of the semiconductor ceramic. Accordingly, there are provided satisfactory rise characteristics even if an alkali metal element is present.

A semiconductor ceramic includes a BaTiO-based composition, as a main component, having a perovskite structure represented by general formula ABO. Part of the A site Ba is replaced with an alkali metal element, Bi, Ca, Sr, and a rare-earth element. When the molar amounts of Ca and Sr are x and y, respectively, and the total number of moles of the elements constituting the A site is 1 mole, 0.05&#x2266;x&#x2266;0.20, 0.02&#x2266;y&#x2266;0.12, and 2x+5y&#x2266;0.7. A PTC thermistor includes a component body formed of the semiconductor ceramic. Even when an alkali metal element and Bi are present, there is provided a lead-free semiconductor ceramic with high reliability in which the surface discoloration is not caused and the degradation of resistance over time can be suppressed even after the application of an electric current for a long time.

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Nagaokakyo, Japan

Naoaki Abe