Structures, phase transitions and microwave dielectric properties of the 6H perovskites Ba{sub 3}BSb{sub 2}O{sub 9}, B=Mg, Ca, Sr, Ba
- School of Chemistry, University of Sydney, Sydney, NSW 2006 (Australia)
- Bragg Institute, ANSTO, PMB 1, Menai, NSW 2234 (Australia)
- Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ (United Kingdom)
We present a complete temperature-composition phase diagram for Ba{sub 3}BSb{sub 2}O{sub 9}, B=Mg, Ca, Sr, Ba, along with their electrical behavior as a function of B. These compounds have long been recognized as 6H-type perovskites, but (with the exception of B=Mg) their exact structures and properties were unknown due to their low symmetries, temperature-dependent phase transitions, and difficulties in synthesizing pure samples. The full range of possible space group symmetries is observed, from ideal hexagonal P6{sub 3}/mmc to monoclinic C2/c to triclinic P1-bar. Direct second-order transitions between these phases are plausible according to group theory, and no evidence was seen for any further intermediate phases. The phase diagram with respect to temperature and the effective ionic radius of B is remarkably symmetrical for B=Mg, Ca, and Sr. For B=Ba, a first-order phase transition to a locally distorted phase allows a metastable hexagonal phase to persist to lower temperatures than expected before decomposing around 600 K. Electrical measurements revealed that dielectric permittivity corrected for porosity does not change significantly as a function of B and is in a good agreement with the values predicted by the Clausius-Mossotti equation. - Graphical abstract: Thermodynamic phase diagram for Ba{sub 3}BSb{sub 2}O{sub 9}, B=Mg, Ca, and Sr, as a function of temperature T and effective ionic radius (IR) of the B{sup 2+} cation.
- OSTI ID:
- 21212217
- Journal Information:
- Journal of Solid State Chemistry, Vol. 182, Issue 3; Other Information: DOI: 10.1016/j.jssc.2008.11.026; PII: S0022-4596(08)00610-5; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
BARIUM COMPOUNDS
CALCIUM COMPOUNDS
CALORIMETRY
DIELECTRIC MATERIALS
GROUP THEORY
HCP LATTICES
MAGNESIUM COMPOUNDS
MICROWAVE RADIATION
MONOCLINIC LATTICES
NEUTRON DIFFRACTION
OXIDES
PERMITTIVITY
PEROVSKITE
PHASE DIAGRAMS
PHASE TRANSFORMATIONS
SPACE GROUPS
STRONTIUM COMPOUNDS
TEMPERATURE DEPENDENCE
THERMAL GRAVIMETRIC ANALYSIS
X-RAY DIFFRACTION