Effects of Li₂CO₃ addition on the microstructural and electrical properties of lead-free piezoelectric (Ba,Ca)(Ti,Zr)O₃ ceramics sintered in air or a reducing atmosphere

The effects of Li₂CO₃ addition on microstructural and piezoelectric properties of lead-free (Ba,Ca)(Ti,Zr)O₃ piezoceramics sintered in either air or a reducing atmosphere were investigated. A reducing atmosphere was maintained by controlling the oxygen partial pressure with a suitable mixture of Ar, H₂, and CO₂ gases. Li₂CO₃ addition promoted grain growth in the ceramic samples, which were highly polarized following poling treatment. An optimal amount of Li₂CO₃ was necessary for maintaining controlled grain growth and high density during sintering. The resulting ceramics exhibited high electrical resistivity and improved piezoelectric properties. The dielectric properties of the ceramics prepared with Li₂CO₃ exhibited a similar dependence on temperature, regardless of the sintering atmosphere or amount of Li₂CO₃ added. Even though the amount of added Li₂CO₃ ranged from 0.3 to 9 mol%, the residual Li content in the ceramics after sintering was approximately 0.1 mol%. The sintered bodies exhibited good electrical resistivity (>10¹² Ω cm) and relatively high piezoelectric constants (d ₃₃) of ∼400 pC/N.