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 (Ba0.95Ca0.05)(Zr0.05Ti0.95-x (Zn1/3Ta2/3) 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 (d 33 ∼ 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 (d 33 = 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.