Orthorhombic–tetragonal phase coexistence and enhanced piezoelectric properties at room temperature in Zn and Ta modified (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 ceramics through the synergistic effect of lattice distortion

Abstract

This study provides a fundamental understanding of the enhanced piezoelectric properties in ABO₃ perovskite based lead-free piezoelectric materials. For this we synthesized (Ba_0.95Ca_0.05)(Zr_0.05Ti_0.95−x(Zn_1/3Ta_2/3)_x)O₃((1 − x)BCZT–(x)ZT) (x = 0.00, 0.005, 0.01, and 0.02) solid solutions exhibiting high piezoelectric response. The (1 − x)BCZT–xZT materials are synthesized by a high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00–0.02). In-depth exploratory research is performed on the structural, dielectric, ferroelectric, and piezoelectric properties of (1 − x)BCZT–(x)ZT ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca²⁺, Zr⁴⁺, Zr²⁺ and Ta⁵⁺ are well dispersed within the BaTiO₃ lattice. For all (1 − x)BCZT–(x)ZT ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The c/a ratio of the tetragonal phase greatly influenced the electric properties of the ceramics. The c/a ratio of the tetragonal phase increases from 1.0112 for x = 0 to 1.0157 for x = 0.005 and subsequently decreases to 1.0038 for x = 0.02. When the c/a of the tetragonal phase reaches its maximum value, the ceramic with x = 0.005 has the best piezoelectricity (d₃₃ ∼ 297 pC N⁻¹). The calculated degree of relaxation (γ) increases with the increase in BZT content, indicating that the BCZT–xBZT ceramics are ferroelectric materials with diffuse phase transition. Main dielectric, piezoelectric and ferroelectric parameters of (1−x)BCZT–xZT ceramics were optimized around x = 0.005 with a high piezoelectric coefficient (d₃₃ = 297 pC N⁻¹), a remnant polarization (P_r = 7.58 μC cm⁻²), spontaneous polarization (P_s = 10.25 μC cm⁻²) and a high dielectric constant (ε_max,T^c = 4449 at T_c and 2330 near RT) at 1 kHz, indicating promising applications for lead-free piezoelectric ceramics.