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Abnormal reoxidation effects in Ba‐excess La‐doped BaTiO 3 ceramics prepared by the reduction‐reoxidation method
Author(s) -
Zu Hao,
Chen Tao,
Gao Chao,
Fu Qiuyun,
Zhou Dongxiang,
Hu Yunxiang,
Zheng Zhiping,
Luo Wei
Publication year - 2017
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14823
Subject(s) - electrical resistivity and conductivity , temperature coefficient , ceramic , materials science , thermistor , grain boundary , doping , mineralogy , analytical chemistry (journal) , phase (matter) , perovskite (structure) , inorganic chemistry , composite material , chemistry , microstructure , optoelectronics , crystallography , electrical engineering , organic chemistry , chromatography , engineering
Ba‐excess La‐doped BaTiO 3 ceramics have been successfully applied to prepare laminated chip thermistor. Ceramics were firstly fired in a high‐purity N 2 flow and then reoxidized in air to obtain positive temperature coefficient of resistivity effect. However, an abnormal reduction trend of room‐temperature ( RT ) resistivity was found to be always beginning at ~800°C during reoxidation. This anomaly was found closely correlated with the insulating second phase (Ba 2 TiO 4 ) at grain boundary, which destroyed conducting pathways between semiconducting BaTiO 3 grains. When reoxidation temperature was up to ~800°C, the insulating Ba 2 TiO 4 could be gradually consumed and then conducting pathways reestablished leading to RT resistivity reduction. To further prove the proposed explanation, the reoxidation effects of TiO 2 ‐added ceramics were also studied, in which no Ba 2 TiO 4 existed and certainly the abnormal RT resistivity reduction disappeared.