Fabrication of Reduction-resistant BaTiO₃-based Lead-free Piezoelectric Ceramics and Approach for Improving Their Properties

Abstract

Piezoelectric materials are currently applied in various electronic devices. Multilayer technology has become indispensable for the miniaturization of electronic devices. In this case, the development of materials that do not contain toxic elements has been receiving considerable attention because of environmental issues. This tutorial paper describes the processing of reduction-resistant BaTiO₃-based piezoceramics with improved properties for multilayer-type component using base metal internal electrodes. Nonreducible BaTiO₃-based ceramics that exhibited a high piezoelectric constant equivalent to that of samples prepared in air were successfully fabricated at temperatures below the melting point of Ni metal. Grain-oriented ceramics were prepared by the reactive templated grain growth method using platelike perovskite oxide particles. The electrical properties of the BaTiO₃-based ceramics, sintered in the reducing atmosphere, were markedly improved as a result of fabricating grain-oriented samples. A desired reducing atmosphere was achieved by controlling the oxygen partial pressure with a suitable mixture of Ar, H₂, and CO₂ gases. Optimizing the amount of Li₂CO₃ added to composition modified BaTiO₃-based ceramics sintered under a low oxygen partial pressure resulted in improved piezoelectric properties while maintaining the high sintered density. Reduction-resistant BaTiO₃-based ceramics developed in this study are promising lead-free materials for applications in multilayer piezoelectric components.