Different Types of Cation Ordering and Dielectric Properties in the Complex Perovskine Ca(Ca1/3Nb^2/3^)O3

Published

January 1, 2001

Author(s)

Igor Levin, Julia Y. Chan, Richard G. Geyer, James E. Maslar, Terrell A. Vanderah

Abstract

In the present work the effects of cation ordering on delectric properties were isolated by investigating three polymorphs of Ca(Cu_1/3Nb_2/3O₃ that feature different arrangements of the Ca²⁺ and Nb⁵⁺ cations on the B-sites of the perovskite structure. Dielectric measurements at frequencies above 1 Ghz revealed a systematic dependence of the properties on the type of cation ordering. In particular, the structure with 2:1 ordering exhibited a lower dielectric constant and a significantly more negative tempertaure coefficient of the resonance frequency than the structures with 1:1 and newly described K-1/4[111]^*c ordering. Rietveld refinements of structural models for the three Ca₄Nb₂O₉ polymorphs were conducted using X-ray and neutron powder diffraction data to elucidate structural details which correlate with the changes in dielectric properties. In all three polymorphs the cation ordering was combined with the same b-b-c+ octahedral tilt system, and the structural refinements yielded similar magnitudes of the tilting angles. The most significant structural difference between the different cation-ordering patterns was in the coordination environment of Nb⁵⁺. Analysis of the refined bond distances indicated the largest distortion of the Nb-environment in the 2:1 ordered structure; the average distortion in the 1:1 polymorph was the least, and that in the k-1/4[111]^*c ordered structure was intermediate. The increased fraction of strongly compressed Nb-O bonds in the 2:1 structure associated with the large distortion was correlated with the decrease in dielectric constant and more negative value of temperature coefficient of the resonant frequency obtained for this polymorph.

Citation

Journal of Solid State Chemistry

Volume

156

Issue

1

Pub Type

Journals

Keywords

cation ordering, dielectric properties, octahedral tilting, perovskite

Citation

Levin, I. , Chan, J. , Geyer, R. , Maslar, J. and Vanderah, T. (2001), Different Types of Cation Ordering and Dielectric Properties in the Complex Perovskine Ca(Ca_1/3Nb^2/3^)O₃, Journal of Solid State Chemistry (Accessed December 22, 2024)