Phase Transitions and Microwave Dielectric Properties in the Perovskite-Like Ca(Al0.5Nb0.5)O3-CaTiO3 System

Published

July 1, 2001

Author(s)

Igor Levin, Julia Y. Chan, James E. Maslar, Terrell A. Vanderah, S M. Bell

Abstract

Phase transitions and microwave dielectric properties in (1-x)Ca(Al0.5Nb0.5)O3 xCaTiO3 system were analyzed using X-ray and neutron powder diffraction, transmission electron microscopy, Raman spectroscopy, and dielectric measurements at microwave frequencies (2-8 GHz). Rieveld structural refinements demonstrated that both end-compounds exhibit similar octahedral tilted frameworks, while in Ca(Al0.5Nb0.5)O3, tilting is superimposed onto NaCl-type ordering of Al and Nb on the B-sites. Accordingly, the room-temperature structures of CaTiO3 and Ca(Al0.5Nb0.5)O3 are described by orthorhombic Pbnm and monoclinic P21/n symmetries, respectively, with similar lattice parameters, ?2acx?2acx2ac (where ac is the lattice parameter of cubic perovskite). Thus, the (1-x)Ca(Al0.5Nb0.5)O3?xCaTiO3 system features both cation ordering and octahedral tilting phase transitions. The Ca(A10.5Nb0.5)O3 structure remains ordered at least up to 1625?C. However, the temperature of the order/disorder transition decreases rapidly with increasing Ti-content, which correlates with a progressive increase of cation disorder in the specimens. A disordered structure is attained at x=0.5. Raman peaks associated primarily with cation ordering were readily identified by correlation with intensities of superlattice reflections in the X-ray and electron diffraction patterns. For the solid solutions , the non-linear dependence of both permittivity and the temperature coefficient of the resonant frequency on Ti-content corresponds to a linear dependence of the macroscopic polarizability on composition; that is, the oxide addivitity rule was closely obeyed. Therefore, this rule can be used to predict ? and ?f for any intermediate compostition from the permittivities and temperature coefficients of permittivity of the end compounds. A zero temperature coefficient of the resonant frequency occurs at the composition x?0.5 with a relative permittivity of 50 and a Qf value of approximately 30,000 GHz (@ 4 GHz).

Citation

Journal of Applied Physics

Volume

90

Issue

No. 2

Pub Type

Journals

Keywords

cation ordering, dielectric properties, electron microscopy, microwave dielectrics, neutron diffraction, octahedral tilting, perovskite, raman, x-ray diffraction

Citation

Levin, I. , Chan, J. , Maslar, J. , Vanderah, T. and Bell, S. (2001), Phase Transitions and Microwave Dielectric Properties in the Perovskite-Like Ca(Al_0.5Nb_0.5)O₃-CaTiO₃ System, Journal of Applied Physics (Accessed April 24, 2024)