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Positive Temperature Coefficient of Resistivity Effect in Highly Donor–Doped Barium Titanate
Author(s) -
Makovec Darko,
Ule Nina,
Drofenik Miha
Publication year - 2001
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/j.1151-2916.2001.tb00828.x
Subject(s) - electrical resistivity and conductivity , sintering , barium titanate , materials science , reducing atmosphere , temperature coefficient , annealing (glass) , doping , analytical chemistry (journal) , ceramic , mineralogy , grain growth , precipitation , grain boundary , grain size , metallurgy , composite material , chemistry , microstructure , physics , optoelectronics , chromatography , meteorology , electrical engineering , engineering
BaTiO 3 ceramics doped with different La concentrations (0–12 mol%) were prepared by sintering under the reducing conditions of a nitrogen atmosphere containing 1% hydrogen. The critical donor concentration that causes blocking of the exaggerated grain growth was observed to be ∼10 mol% La. The samples, which were semiconducting after sintering under reducing conditions, were subsequently reoxidized by annealing in air to induce the positive temperature coefficient of resistivity (PTCR) effect. After reoxidation at 1150°C a noticeable PTCR effect was observed in the samples doped with La concentrations as high as 2.5 mol%. The room‐temperature resistivity after reoxidation was found to increase with increasing donor concentration due to an increase in the thickness of the insulating layers at the grain boundaries. TEM analysis showed that reoxidation of the samples caused precipitation of the Ti‐rich compound Ba 6 Ti 17 O 40 inside the doped BaTiO 3 ‐matrix grains.