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( Ba 1+ x TiO 3 )–( Bi 0.5 Na 0.5 TiO 3 ) Lead‐Free, Positive Temperature Coefficient of Resistivity Ceramics: PTC Behavior and Atomic Level Microstructures
Author(s) -
Kaneko Yasushi,
Azough Feridoon,
Kida Toshiki,
Ito Kentaro,
Shimada Takeshi,
Minemura Tetsuroh,
Schaffer Bernhard,
Freer Robert
Publication year - 2012
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.1551-2916.2012.05423.x
Subject(s) - materials science , electrical resistivity and conductivity , tetragonal crystal system , analytical chemistry (journal) , perovskite (structure) , high resolution transmission electron microscopy , stacking fault , grain boundary , crystallography , temperature coefficient , mineralogy , transmission electron microscopy , crystal structure , dislocation , chemistry , nanotechnology , microstructure , metallurgy , chromatography , composite material , electrical engineering , engineering
Positive temperature coefficient of resistivity (PTCR) ceramics of 0.912( Ba 1+ x TiO 3 )–0.088( Bi 0.5 Na 0.5 TiO 3 ) ( BT – BNT ) ( x = − 0.03 to 0.03) were prepared using the mixed oxide route and sintered at 1340°C for 4 h. Products were predominantly single phase with a tetragonal structure and grains in 2–6 μm size containing 90° ferroelectric domains. Samples with Ti / Ba > 1 contained second‐phase Ba 6 Ti 17 O 40 . HRTEM and aberration‐corrected Z ‐contrast high angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) suggested that the dopants, Bi and Na , occupy the Ba site of the perovskite lattice, and revealed the presence of dissociated dislocations in x = − 0.03 and x = 0.00 materials. The interval between two partial dislocations was 1.9–3.4 nm, yielding stacking fault energies of 363–649 mJ/m 2 . The PTCR behavior of the ceramics increased with Ti / Ba content, reaching a maximum of six decades change in resistivity for x = − 0.03. The anomalous increase in resistivity depends critically on stoichiometry, increasing with the Ti / Ba ratio; this in turn is directly correlated with an increase in the amount of second‐phase Ba 6 Ti 17 O 40 , an increase in the stacking fault energy, and an increase in the tilt angle of the grain boundaries.