Structure-composition-property relationships of stoichiometric and non-stoichiometric "Bi12MO20" sillenites

The structure-composition-property relationships of sillenite-type compounds Bi12MxO20±δ, where M = Zn2+, Mg2+, Fe3+, Al3+, In3+, Ga3+, B3+, Si4+, V5+ and P5+ have been investigated. This has enabled improved understanding associated with the following aspects: (i) approval of the structural model of Radaev and co-workers’ (R model); (ii) validity of the general formula for sillenites suggested by Valant and Suvorov (VS); (iii) rationalisation of the linear trend(s) between dopant ion (M) size and unit cell length as reported by Poleti et al.; (iv) the origins of the low (LT) and high temperature (HT) bulk dielectric relaxation effects in sillenites; (v) the variation in bulk conductivity of stoichiometric and non-stoichiometric sillenites; (vi) potential physical applications of sillenites as Low Temperature Co-fired Ceramics (LTCC) dielectrics and/or mixed ionic-electronic conductors.