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Role of Liquid Phase in PTCR Characteristics of (Ba 0.7 Sr 0.3 )TiO 3 Ceramics
Author(s) -
Lee JungKun,
Park JongSung,
Hong KugSun,
Ko KyungHyun,
Lee ByungChan
Publication year - 2002
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.1151-2916.2002.tb00241.x
Subject(s) - materials science , dielectric spectroscopy , high resolution transmission electron microscopy , grain boundary , analytical chemistry (journal) , transmission electron microscopy , spectroscopy , precipitation , phase (matter) , ceramic , scanning electron microscope , acceptor , mineralogy , microstructure , chemistry , composite material , nanotechnology , condensed matter physics , electrochemistry , quantum mechanics , meteorology , physics , organic chemistry , electrode , chromatography
The role of liquid phase in the enhancement of the PTCR (positive temperature coefficient of resistance) effect in (Ba 0.7 Sr 0.3 )TiO 3 (BST) with the addition of AST (4Al 2 O 3 · 9SiO 2 · 3TiO 2 ) is investigated in this paper. The AST–BST samples were characterized with optical microscopy, transmission electron microscopy, energy‐dispersive spectroscopy, and impedance spectroscopy. Microscopic observations showed that slower cooling might facilitate the precipitation of the (Ba,Sr)TiO 3 phase from the liquid phase on matrix grains since the amount of liquid phase was reduced with a decreasing cooling rate. Impedance spectroscopy indicated that this variation accompanied the change in the intrinsic properties of grain boundaries, which could not be explained by well‐known oxidation effects. With the aid of a brick‐layer model and high‐resolution transmission electron microscopy (HRTEM), it appeared that the change in electrical characteristics of grain boundaries with decreasing cooling rate originated from the precipitation of (Ba,Sr)TiO 3 . Finally, the effect of precipitated (Ba,Sr)TiO 3 on the PTCR characteristics is discussed in terms of the acceptor‐state density and the polarization state at grain boundaries.