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Microwave dielectric properties and crystal structures of Mg 0.7 Al 2.2 O 4 and Mg 0.4 Al 2.4 O 4 ceramics with defect structures
Author(s) -
Takahashi Susumu,
Kan Akinori,
Ogawa Hirotaka
Publication year - 2017
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14847
Subject(s) - octahedron , crystal structure , rietveld refinement , crystallography , ceramic , crystal chemistry , dielectric , materials science , tetrahedron , mineralogy , analytical chemistry (journal) , chemistry , metallurgy , optoelectronics , chromatography
Mg 0.7 Al 2.2 O 4 and Mg 0.4 Al 2.4 O 4 ceramics with cation vacancies were synthesized using the molten salt method, and the relationships between the microwave dielectric properties and crystal structures of these materials were investigated. The 27 Al NMR spectra of these ceramics indicate that the preferential occupation of tetrahedral sites by Al 3+ cations was enhanced by the introduction of cation vacancies. The λ values of Mg 0.7 Al 2.2 O 4 and Mg 0.4 Al 2.4 O 4 ceramics fired at 1600°C, which correspond to the fraction of Al 3+ cations in tetrahedral sites, were 0.37 and 0.60, respectively. Crystal structure refinements using the Rietveld method suggest that cation vacancies are preferentially located at octahedral sites in both ceramics. The ε r and Q · f values of a Mg 0.7 Al 2.2 O 4 ceramic fired at 1600°C were 7.7 and 201 111 GHz, respectively, while those of a Mg 0.4 Al 2.4 O 4 ceramic fired at 1600°C were 7.5 and 232 301 GHz, respectively. These data demonstrate that the preferential occupation of tetrahedral sites by Al 3+ cations following the introduction of cation vacancies enhances the Q · f value.