Effects of pH on the crystal structure, morphology and microwave dielectric properties of Bi12TiO20 ceramics synthesized by citrate sol–gel method

Abstract

Bi12TiO20 ceramics were prepared via a modified sol–gel route using citric acid as a metal chelating agent. The pH value of the initial precursor was adjusted from 6 to 13 by the addition of ammonium hydroxide (NH4OH). The effects of pH value on the formation of chelate complex between citric acid and metal ions were systematically investigated in this work. Furthermore, the crystal structure, microstructure and microwave dielectric properties of Bi12TiO20 ceramics derived at various pH values were characterized. Scanning electron microscopy and energy dispersive spectroscopy indicated that a single Bi12TiO20 phase with high relative densities above 96 % of the theoretical density was successfully achieved at pH 11. The variations in density, ionic polarizability and microstructure had a remarkable effect on the microwave dielectric properties of Bi12TiO20 ceramics. In the case of pH 11, Bi12TiO20 ceramics sintered at 750 °C exhibited promising microwave dielectric properties: e r = 39.55, Q × f = 3950 GHz, and τ f = − 17 ppm/°C, indicating that they were promising dielectric candidates for LTCC applications.