Enhanced piezoelectric properties in high-TC Bi5Ti3FeO15 via dysprosium substitution: a rare-earth doping approach for superior performance

The development of iron-containing Aurivillius-phase bismuth layer-structured ferroelectrics (BLSFs) has garnered considerable attention due to their unique multiferroic properties, characterized by the coexistence of ferroelectric and magnetic ordering. Among these materials, bismuth titanate-ferrite (Bi₅Ti₃FeO₁₅) stands out as a prominent candidate for high-temperature piezoelectric applications, given its elevated Curie temperature (T_C) of 760 °C. Despite its potential, the practical utilization of Bi₅Ti₃FeO₁₅ in high-temperature piezoelectric devices is limited by low resistance at elevated temperatures and poor piezoelectric performance. To address these issues, we explored a composition optimization strategy involving the partial substitution of bismuth ions with rare-earth dysprosium (Dy) ions to enhance piezoelectric performance and direct-current (DC) electrical resistivity of Bi₅Ti₃FeO₁₅. This substitution aims to mitigate the volatility of bismuth ions and stabilize the (Bi₂O₂)²⁺ layer, thereby reducing oxygen vacancy concentration. We successfully synthesized Bi_5-xDy_xTi₃FeO₁₅ (BTF-100xDy) oxide compounds using a solid-state reaction method. Our experimental results demonstrate that dysprosium-substituted Bi₅Ti₃FeO₁₅ exhibits markedly enhanced piezoelectric performance compared to the unmodified Bi₅Ti₃FeO₁₅. Specifically, the BTF-5Dy composition achieved a significant increase in the piezoelectric constant (d₃₃) to 23.1 pC/N, which is approximately three times higher than that of the unmodified Bi₅Ti₃FeO₁₅ (7.1 pC/N). The temperature-dependent measurements of DC electrical resistivity revealed that dysprosium substitution substantially improves the material’s electrical resistivity at elevated temperatures. Additionally, BTF-5Dy exhibited a high T_C of 787 °C, a low dielectric loss tanδ (~ 0.38% at 1 MHz), and good thermal stability of electromechanical properties up to 300 °C. These improvements are attributed to lattice distortion and reduced oxygen vacancies. Collectively, these findings suggest that dysprosium-substituted Bi₅Ti₃FeO₁₅ ceramics hold great promise as high-performance materials for high-temperature piezoelectric applications.