Evaluating the polymorphic phase transition in calcium-doped Ba(Zr_0.05Ti_0.95)O₃: a lead-free piezoelectric ceramic

Structural and dielectric investigations were carried out on a perovskite lead-free (Ba_1−xCa_x)(Zr_0.05Ti_0.95)O₃ ferroelectric ceramic for x = 0.03, 0.05, 0.08, 0.10, 0.12 and 0.15. The room-temperature structural analysis reveals a crossover from orthorhombic to tetragonal crystal structure near x = 0.10. A coexistence of tetragonal (P4mm) and orthorhombic (Pmm2) structure is observed in the composition range 0.05 ≤ x ≤ 0.10. The fraction of tetragonal phase increases from 27% for x = 0.05 to 71% for x = 0.10. The dielectric measurements show that the tetragonal to orthorhombic and rhombohedral to orthorhombic transition temperatures decrease with an increase in Ca²⁺ content, while the cubic to tetragonal transition temperature remains the same. It is also shown that for the tetragonal to orthorhombic transition a phase coexistence occurs over a temperature range of about 18 K. The coexistence range covers room temperature for intermediate compositions: x = 0.05, 0.08 and 0.10. Therefore, higher dielectric and piezoelectric properties are observed in these compositions.