Lu F, Wang X, Pan Z, Pan F, Chai S, Liang C, Wang Q, Wang J, Fang L, Kuang X, Jing X. Nanometer-scale separation of d(10) Zn(2+)-layers and twin-shift competition in Ba8ZnNb6O24-based 8-layered hexagonal perovskites.
Dalton Trans 2015;
44:13173-85. [PMID:
26110444 DOI:
10.1039/c5dt00859j]
[Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The 8-layered shifted hexagonal perovskite compound Ba8ZnNb6O24 was isolated via controlling the ZnO volatilization, which features long-range B-cation ordering with nanometer-scale separation by ∼1.9 nm of octahedral d(10) cationic (Zn(2+)) layers within the purely corner-sharing octahedral d(0) cationic (Nb(5+)) host. The long-range ordering of the B-site vacancy and out-of-center distortion of the highly-charged d(0) Nb(5+) that is assisted by the second-order Jahn-Teller effect contribute to this unusual B-cation ordering in Ba8ZnNb6O24. A small amount (∼15%) of d(10) Sb(5+) substitution for Nb(5+) in Ba8ZnNb6-xSbxO24 dramatically transformed the shifted structure to a twinned structure, in contrast with the Ba8ZnNb6-xTaxO24 case requiring 50% d(0) Ta(5+) substitution for Nb(5+) for such a shift-to-twin transformation. Multiple factors including B-cationic sizes, electrostatic repulsion forces, long-range ordering of B-site vacancies, and bonding preferences arising from a covalent contribution to the B-O bonding that includes out-of-center octahedral distortion and the B-O-B bonding angle could subtly contribute to the twin-shift phase competition of B-site deficient 8-layered hexagonal perovskites Ba8B7O24. The ceramics of new shifted Ba8ZnNb6O24 and twinned Ba8ZnNb5.1Sb0.9O24 compounds exhibited good microwave dielectric properties (εr ∼ 35, Qf ∼ 36 200-43 400 GHz and τf ∼ 38-44 ppm/°C).
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