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Polymorphism and Dielectric Properties of Nb‐Doped BaTiO 3
Author(s) -
Masó Nahum,
Beltrán Héctor,
Cordoncillo Eloisa,
Sinclair Derek C.,
West Anthony R.
Publication year - 2008
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.1551-2916.2007.02083.x
Subject(s) - ferroelectricity , permittivity , materials science , dielectric , phase diagram , doping , analytical chemistry (journal) , relative permittivity , mineralogy , phase transition , condensed matter physics , phase (matter) , chemistry , optoelectronics , physics , organic chemistry , chromatography
A working subsolidus phase diagram for the system BaTiO 3 –Ba 5 Nb 4 O 15 has been determined by firing sol–gel‐synthesized samples over a range of temperatures. The main difference from previous diagrams is the greater extent of the Nb‐doped BaTiO 3 cubic solid solutions, BaTi 1−5 x Nb 4 x O 3 , at lower temperatures with x extending to 0.09 at 900°C, but only 0.05 at 1400°C. Electrical property measurements show that compositions with large x ( x ≥0.0025) are highly insulating for pellets sintered at 1300°C in air, followed by a slow cool. Compositions with low x , however, exhibit a residual semiconducting grain core and are not fully reoxidized readily. Composition dependence of the dielectric properties shows a continuous and smooth transition from classic ferroelectric behavior with pure BaTiO 3 to normal dielectric response with a temperature‐independent relative permittivity of approximately 22–24 for x >∼0.08. At intermediate compositions, ranges of both relaxor ferroelectric and quasi‐ferroelectric behavior are observed. Possible reasons for an observed anomalous increase in value of the permittivity at the ferroelectric transition temperature at low x , which is superposed on an overall decrease in permittivity with increasing x , are discussed.