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Characterization of Cation-Ordering Induced Structures in Ba(Mg1/3Nb2/3)O3-BazrO3 Microwave Ceramics.

Published online by Cambridge University Press:  15 February 2011

M. A. Akbas  and
P. K. Davies
M. A. Akbas
Affiliation:
Dept. of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104–6272
P. K. Davies
Affiliation:
Dept. of Materials Science & Engineering, University of Pennsylvania, 3231 Walnut St., Philadelphia, PA 19104–6272
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Abstract

Compositions in the Ba(Mg1/3Nb2/3)O3-BazrO3 (BMN-BZ) pseudo-binary system were prepared to evaluate the effect of BaZrO3 on the B-site cation ordering. While pure BMN adopts a 1:2 ordered structure, space group , 5 to 15 mole% additions of BZ stabilize a cubic 1:1 ordered phase with a doubled perovskite repeat. At higher levels of substitution (>25 mole% BZ), the B-site cations are disordered. Analytical TEM studies revealed that the 1:1 ordering is limited to nanometer-sized domains and the microstructure was found to strongly depend on the thermal history of the ceramics. For example, a cooling rate of 300°C/hr from a sintering temperature of 1640°C produced a partially ordered microstructure comprised of 4–5nm 1:1 domains dispersed in a disordered matrix. A completely ordered structure with 30–40 nm domains could be achieved when the cooling rate was reduced to 10°C/hr. The structure of the ordered 1:1 phases is interpreted using a “random layer” model in which one site is occupied exclusively by Nb, and the second contains a random distribution of all the remaining cations. Similar thermal annealing experiments were also conducted in an attempt to grow the 1:1 ordered domains in PMN-type (PbMg1/3Nb2/303) relaxor ferroelectric ceramics. Through experiments on PbZr03 (PZ)-doped PMT (PbMg1/3Ta2/3O3), the first observation of thermally induced domain growth in this class of relaxor ceramics are presented. These results cannot be explained by the widely accepted “space charge” model for relaxor ferroelectrics, but instead favor a charge-balanced random layer model for the 1:1 cation order.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 453: Symposium R – Solid State Chemistry of Inorganic Materials , 1996 , 483
Copyright
Copyright © Materials Research Society 1997

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References

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