Preparation of monolithic barium titanate xerogels by sol–gel processing and the dielectric properties of their sintered bodies

Abstract

Monolithic xerogels of crystalline barium titanate, with dimensions of ∼3 mm thick and ∼6 mm in diameter, have been produced by sol–gel processing using metal alkoxides. An excess amount of water with the H2O/Ba ratio≳100 (for hydrolysis of the barium titanate precursor alkoxides) and aging time≳8 days were necessary to produce the monolithic crystalline xerogels without breaking during drying (at 90 °C). The barium titanate xerogels as-dried, with a porosity of about 70%, have been found to consist of crystalline grains in the range of 10–20 nm. Firing the xerogels at 1000 °C in air yielded porous barium titanate ceramics with an average grain size around 50 nm and a decreased porosity around 60%. The dielectric constant (εr)–temperature (T) characteristics of these ceramics have been found to be rather flat below 120 °C with a broad peak around this temperature, and those above 120 °C showed a specific behavior of ferroelectric materials described by a Curie–Weiss equation, εr=C/(T–T0), with C≊2×104 K and T0≊230 K (−43 °C); although these values are quite different from those of ferroelectric barium titanate.