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Tunability of τf in perovskites and related compounds

Published online by Cambridge University Press:  31 January 2011

P. L. Wise
Affiliation:
Department of Engineering Materials, Sir Robert Hadfield Building, University of Sheffield, Sheffield, S1 3JD, United Kingdom
I. M. Reaney
Affiliation:
Department of Engineering Materials, Sir Robert Hadfield Building, University of Sheffield, Sheffield, S1 3JD, United Kingdom
W. E. Lee
Affiliation:
Department of Engineering Materials, Sir Robert Hadfield Building, University of Sheffield, Sheffield, S1 3JD, United Kingdom
D. M. Iddles
Affiliation:
Filtronic Comtek, Enterprise Drive, Station Rd., Four Ashes, Wolverhampton, WV10 7DB United Kingdom
D. S. Cannell
Affiliation:
Filtronic Comtek, Enterprise Drive, Station Rd., Four Ashes, Wolverhampton, WV10 7DB United Kingdom
T. J. Price
Affiliation:
Filtronic Comtek, Enterprise Drive, Station Rd., Four Ashes, Wolverhampton, WV10 7DB United Kingdom
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Abstract

Tuning the temperature coefficient of resonant frequency (τf) in microwave dielectrics has been attributed to two main mechanisms: (i) dilution of the average ionic polarizability; (ii) the onset of an octahedral tilt transition above room temperature. The contributions of each mechanism have been isolated using ceramics in the Srn+1TinO3n+1, SrxCa1−x)3Ti2O7, and (SrxCa1−x)TiO3 series. In the Srn+1TinO3n+1 series, relative permittivity (εr) and τf are linearly proportional over a broad range of values, 100–37 and 800–140 ppm/°C, n = 4 and 1, respectively. No structural phase transitions occur on cooling from the prototype symmetry, and the mechanism of tuning is attributed solely to dilution of the average ionic polarizability as the SrO:SrTiO3 ratio increases. Exchanging Ca for Sr in the (SrxCa1−x)3Ti2O7 series resulted in an 80% reduction in the magnitude of τf from +320 to +50 ppm/°C but only 21% in permittivity (58 to 46). The effect was nonlinear and attributed primarily to the onset of a phase transition involving rotations of the octahedra on cooling. Superlattice reflections associated with the octahedral tilt transition have been identified.

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Articles
Copyright
Copyright © Materials Research Society 2002

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