Grain-boundary chemistry of barium titanate and strontium titanate. Part 2; Origin of electrical barriers in positive-temperature-coefficient thermistors

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Journal of the American Ceramic Society; (United States)

DOI:https://doi.org/10.1111/j.1151-2916.1990.tb06451.x· OSTI ID:5152133

Chiang, Y M; Takagi, T ^[1]

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1. Dept. of Materials Science and Engineering, Massachusetts Inst. of Technology, Cambridge, MA (US)

This paper reports on scanning transmission electron microscopy (STEM) of positive-temperature-coefficient (PTC) BaTiO{sub 3} thermistors that shows that the grain-boundary oxygen content in as-received (oxidatively cooled) materials, is slightly enriched compared to quenched samples, and the acceptor-rich space-charge present at high temperatures is retained upon cooling. The defect density of the space charge is approximately equal to the acceptor state density at PTC boundaries determined by electrical measurements. Accordingly, it is proposed that the electrical barrier forms when acceptor defects already segregated in the ionic space charge at high temperature become active interface states when compensating donor defects in the grain-boundary core are oxidized. These acceptor defects appear to be primarily barium vacancies, but need not form upon cooling in the manner proposed by Daniels and Wernicke. Acceptor solutes when present can also contribute to barrier formation through space-charge segregation; the increase in interface state density upon addition of Mn is consistent with the magnitude of the expected segregation.

• OSTI ID: 5152133
• Journal Information: Journal of the American Ceramic Society; (United States), Vol. 73:11; ISSN 0002-7820
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
36 MATERIALS SCIENCE
BARIUM COMPOUNDS
ELECTRICAL PROPERTIES
ELECTROCHEMISTRY
GRAIN BOUNDARIES
TITANATES
STRONTIUM COMPOUNDS
DEFECTS
DENSITY
HIGH TEMPERATURE
OXIDATION
OXYGEN
SPACE CHARGE
THERMISTORS
TRANSMISSION ELECTRON MICROSCOPY
VACANCIES
ALKALINE EARTH METAL COMPOUNDS
CHEMICAL REACTIONS
CHEMISTRY
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
ELEMENTS
MICROSCOPY
MICROSTRUCTURE
NONMETALS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POINT DEFECTS
SEMICONDUCTOR DEVICES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
400201* - Chemical & Physicochemical Properties
360204 - Ceramics
Cermets
& Refractories- Physical Properties