Piezoelectricity and excellent temperature stability in nonferroelectric Bi12TiO20–CaTiO3 polar composite ceramics

Abstract

Nonferroelectric Bi₁₂TiO₂₀–CaTiO₃ (BT–CT) composite ceramics were prepared through an interfacial reaction between presynthesized crystalline CaTiO₃ and crystalline Bi₁₂TiO₂₀ phases at various sintering temperatures. After sintering at temperatures above the melting point of Bi₁₂TiO₂₀, both direct and converse piezoelectric effects were observed in these composites for the first time. Because neither CaTiO₃ nor Bi₁₂TiO₂₀ is ferroelectric and because no obvious crystallographic orientation was found in these sintered composites, the temperature gradient-driven plastic flexoelectricity of the grain boundary amorphous phases might be the main poling mechanism. In this work, the highest d₃₃ value of 8 pC N⁻¹ was obtained in the samples sintered at 860 °C, which were found to contain a large amount of amorphous Bi₁₂TiO₂₀ and to possess the lowest density. For these BT–CT polar composite ceramics, the piezoelectric activity, the dielectric loss (tg δ ≈ 0.1%), the mechanical quality factor (Q_m ≈ 2300), the depoling temperature (T_d ≈ 880 °C) and the temperature stability of the resonance frequency are all comparable to those of the well-known bismuth layer-structured ferroelectrics, which indicates that these new polar composite ceramics are promising candidates for high-temperature piezoelectric applications.