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Proposed Phenomenological PTCR Model and Accompanying Phenomenological PTCR Chart
Author(s) -
Huybrechts Ben,
Ishizaiki Kozo,
Takata Masasuke
Publication year - 1994
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.1151-2916.1994.tb06993.x
Subject(s) - acceptor , materials science , chart , dopant , electrical resistivity and conductivity , phenomenological model , doping , curie temperature , grain boundary , sintering , condensed matter physics , thermodynamics , mineralogy , chemistry , metallurgy , electrical engineering , optoelectronics , physics , mathematics , engineering , microstructure , ferromagnetism , statistics
The positive temperature coefficient of resistivity (PTCR) behavior of semiconductive BaTiO 3 is well explained by the Heywang model, which predicts the resistivity behavior above the Curie point based on the acceptor state density at the grain boundaries, the charge carrier density, and the energy gap, E s , between the conduction band and the acceptor levels. However, the relationship between these parameters and the production parameters (sintering time, composition, and cooling rate) is not well understood. Recently, the present authors have found that E s can be increased by thorough oxidation. This increase is attributed to a change in the oxidation state of the acceptor. Based on this finding and results from the literature, a phenomenological PTCR model and an accompanying PTCR chart for acceptor–donor‐codoped BaTiO 3 are proposed to clarify this relationship. The PTCR chart clarifies that acceptor dopant concentrations, oxidation time, and oxygen partial pressure during oxidation or cooling can be optimized simultaneously to obtain optical PTCR properties.