Phase Character and Dielectric Properties of Amphoteric Holmium-Doped Ba0.90Ca0.10(Ti0.95Zr0.05)(2)O-5 Polycrystalline Ceramics

Amphoteric rare-earth ion dopants can improve ferroelectric ceramic electrical performance because of their amphoteric ion radius and valences. Herein, Ho3+-doped Ba0.90Ca0.10(Ti0.95Zr0.05)(2)O-5 ceramics are sintered at 1230 degrees C with as-synthesized nanoparticles. The effects of various holmium contents (x) on the phase, structure, dielectric, and piezoelectric characteristics are investigated. For low x (<1.5 mol%), Ho3+ occupies the Ba2+ or/and Ca2+ sites, leading to high dielectric properties due to decreased oxygen vacancies, while the electrical properties weaken with further increase in x. The ferroelectricity and piezoelectricity also deteriorate when x > 1.5 mol% because of the re-emerged oxygen vacancies and interrupted long-range ordering with large compositional fluctuations. The defect chemistry mechanism at different x contents is deduced in accordance with the phase and electrical properties. The activation energy initially elevates to 1.56 eV and then decreases to 1.35 eV with increasing x. Results indicate that the ceramics are promising candidates for lead-free ferroelectric ceramics.