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Crystal Structures, Modeling, and Dielectric Property Relationships of 2:1 Ordered Ba3MM 2O9 (M = Mg, Ni, Zn; M = Nb, Ta) Perovskites

Published

Author(s)

M W. Lufaso

Abstract

The preparation, modeled and refined crystal structures, and structure-dielectric property relationships of five Ba3MM 2O9 (M = Mg, Ni, Zn; M = Nb, Ta) perovskites are reported. Crystal structure modeling was used to generate initial structure models for Rietveld refinements of the neutron powder diffraction data. Bond valence sums calculated from the bond distances indicate Ba-O bonds are compressed and the M-O and M -O6 bonds are expanded from ideal lengths. A shift of Ta5+ and Nb5+ out of center of the [M O6] octahedra forms three short and three long M -O bonds. The octahedral distortion is driven by the asymmetry in the O bonding network and aided by the second-order Jahn-Teller distortion of the d0 Nb5+ and Ta5+ cations. Differences in the atomic coordination environments in the crystal structures were utilized to propose crystal structure-dielectric property relationships. The coordination of the divalent B-site cation (M2+) was correlated with the temperature coefficient of theresonant frequency (tf); a more under-bonded M2+ exhibited a more negative tf. Also, the nearer the bond valences sums of the B-site cations are to the formal oxidations states, a higher Q f was observed.
Citation
Chemistry of Materials

Keywords

complex perovskites, dielectric properties, Jahn-Teller distortion, microwave ceramics, microwave dielectrics, octahedral distortion, second order

Citation

Lufaso, M. (2017), Crystal Structures, Modeling, and Dielectric Property Relationships of 2:1 Ordered Ba3MM 2O9 (M = Mg, Ni, Zn; M = Nb, Ta) Perovskites, Chemistry of Materials (Accessed April 20, 2024)
Created February 19, 2017