Shrinkage mechanism and phase evolution of fine-grain BaTiO 3 powder compacts containing 10 mol% BaGeO 3 prepared via a precursor route

Abstract

The shrinkage mechanism of BaTiO 3 powder compacts containing 10 mol% BaGeO 3, synthesized by a precursor route and a conventional mixed-oxide method, are described herein. The calcination of a barium titanium germanium 1,2-ethanediolato complex precursor – [Ba(HOC 2H 4OH) 4][Ti 0.9Ge 0.1(OC 2H 4O) 3] ( 1) – at 730 °C leads to a nm-sized Ba(Ti 0.9/Ge 0.1)O 3 powder ( 1a) ( S BET = 16.9 m 2 g −1) consisting of BaTiO 3 and BaGeO 3. Whereas the conventional mixed-oxide method yields a powder ( 2) with a specific surface area of S BET = 2.0 m 2 g −1. Powder compacts of 1a start to shrink at 790 °C and the shrinkage rate reaches a maximum at 908 °C. Dense ceramic bodies can be obtained below the appearance of the liquid melt (1120 °C), therefore the shrinkage of 1a can be described by a solid state sintering mechanism. Otherwise the beginning of the shrinkage of powder 2 is shifted to higher temperatures and the formation of the liquid melt is necessary to obtain dense ceramic bodies. Isothermal dilatometric investigations indicate that the initial stage of sintering is dominated by sliding processes. XRD investigations show that below a sintering temperature of 1200 °C ceramic bodies of 1a consist of tetragonal BaTiO 3 and hexagonal BaGeO 3, whereas temperatures above 1200 °C lead to ceramics containing orthorhombic BaGeO 3, and a temperature of 1350 °C causes the formation of a Ba 2TiGe 2O 8 phase. The phase evolution of ceramic bodies of 2 is similar to 1a, however a Ba 2GeO 4 phase is observed below a temperature of 1100 °C.