BaGeO3 as sintering additive for BaTiO3–MgFe2O4 composite ceramics

Abstract

BaTiO₃–MgFe₂O₄ composites (30 wt% MgFe₂O₄) with a small addition of BaGeO₃ as a sintering additive were synthesized by a one-pot Pechini-like sol–gel process. Nano-crystalline composite powders with a crystallite size of about 10 nm were obtained after reaction at 700 °C for 1 h. Magnetic investigations suggest that the nano-powder is in its superparamagnetic state at room temperature. The addition of BaGeO₃ leads to an improved sintering behaviour. DTA measurements reveal the formation of a liquid phase at 1164(3) °C. Dense ceramic bodies (relative density ≥ 90%) were obtained after sintering for 1 h at 1150 °C. SEM investigations prove a 0–3 connectivity and show that the addition of BaGeO₃ promotes the grain growth leading to particles up to 4 μm. In contrast, fine-grained composite ceramics with smaller particles up to 230 nm were obtained after a two-step sintering process. Magnetic measurements indicate a ferrimagnetic behaviour with coercivity values up to 70 Oe depending on the sintering procedure. Furthermore, addition of BaGeO₃ results in an increase of the relative permittivity, whereas the dissipation factor slightly decreases.