Effect of Bi2O3 excess on morphology and structure of BiNbO4 ceramics

Abstract

Goal of the present research was to fabricate BiNbO4 ceramics from the mixture of powders by the solid state reaction route and pressureless sintering at various temperatures (Ts =870°C and Ts =910°C) and study microstructure, phase composition and crystalline structure of BiNbO4 ceramics. Four batches were fabricated and examined, namely the one fabricated from the stoichiometric mixture of reagent - grade oxide powders, viz. Bi203 and Nb20 5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. It was found that apart from the main orthorhombic a-BiNb04 phase additional phases, namely tetragonal Bi 5Nb3015, and cubic Bi3NbO 7 are possible to form from the mixture of bismuth oxide and niobium oxide. It was found that α-BiNbO4 ceramics exhibited the orthorhombic symmetry identified as Pnna (52). However, small differences in elementary cell parameters were found for the samples sintered from stoichiometric and non-stoichiometric mixture of initial powders.