| 摘要 |
A process for preparing a positive temperature coefficient thermistor is disclosed. This thermistor is comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material, and it has a room-temperature resistivity of less than 5,000 ohm-centimeters, an undegraded resistivity of at least about 1,000,000 ohm-centimeters, a degraded resistivity of at least about 900,000 ohm-centimeters, a ratio between its undegraded resistivity and its room-temperature resistivity of at least about 1,000, and a ratio between its undegraded resistivity and its degraded resistivity not exceeding 2.0. The process of this invention is comprised of the steps of sequentially: (1) providing a powder composition comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material; (2) fabricating the powder composition into a shaped powder compact; (3) sintering said powder compact by subjecting it to a temperature of from about 1150 to about 1450 degrees centigrade for at least about 1 hour, thereby forming a consolidated, sintered body; (4) reducing said sintered body by subjecting it to a temperature of from about 700 to about 1,400 degrees centigrade for at least about 30 minutes while maintaining said sintered body under a reducing atmosphere comprised of hydrogen; and (5) halogenating said reduced, sintered body by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 700 to about 1200 degrees centigrade for at least about 5 minutes.
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