Effects of Excess Barium on the Structure and Electrical Properties of (Ba,Ca)TiO₃ Piezoelectric Ceramics with High Mechanical Quality Factors

Manganese-doped Ba_0.925Ca_0.075TiO₃ lead-free piezoelectric ceramics (abbreviated as BCT) with high mechanical quality factor were synthesized by conventional solid-state reaction method. The effects of excess Ba on the crystal structure, microstructure, and electrical properties of the ceramics were systematically investigated. X-ray diffraction and Raman spectra revealed that Ca²⁺ ions were pushed from Ba sites to Ti sites of BCT when 1.5 mol% extra Ba²⁺ ions were added after sintering. The grain size of the ceramics was decreased by adding extra Ba²⁺ ions. The mechanical quality factor and resistivity of the ceramics decreased dramatically when the excess Ba was more than 1.5 mol%. High piezoelectric coefficients (d₃₃ = 150–190 pC/N) and high mechanical quality factors (Q_m = 1 000–1 200) were obtained in the ceramics when the excess of Ba was between 0.5 mol% and 1 mol%. These results indicated that the properties of BCT ceramics could be tailored by adjusting the content of Ba.