Enhanced Piezoelectric, Ferroelectric, and Electrostrictive Properties of Lead-Free (1-x)BCZT-(x)BCST Electroceramics with Energy Harvesting Capability

Abstract

Next-generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)-free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials' design with multi-phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead-free piezoelectric materials (1-x)Ba_0.95 Ca_0.05 Ti_0.95 Zr_0.05 O₃ -(x)Ba_0.95 Ca_0.05 Ti_0.95 Sn_0.05 O₃ , are reported, which are represented as (1-x)BCZT-(x)BCST, with demonstrated excellent properties and energy harvesting performance. The (1-x)BCZT-(x)BCST materials are synthesized by high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-1.00). In-depth exploration research is performed on the structural, dielectric, ferroelectric, and electro-mechanical properties of (1-x)BCZT-(x)BCST 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⁺ , and Sn⁴⁺ are well dispersed within the BaTiO₃ lattice. For all (1-x)BCZT-(x)BCST ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), 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 phase transition temperatures, rhombohedral-orthorhombic (T_R-O ), orthorhombic- tetragonal (T_O-T ), and tetragonal-cubic (T_C ), gradually shift toward lower temperature with increasing x content. For (1-x)BCZT-(x)BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constant ε_r ≈ 1900-3300 (near room temperature), ε_r ≈ 8800-12 900 (near Curie temperature), dielectric loss, tan δ ≈ 0.01-0.02, remanent polarization P_r ≈ 9.4-14 µC cm^-2 , coercive electric field E_c ≈ 2.5-3.6 kV cm^-1 . Further, high electric field-induced strain S ≈ 0.12-0.175%, piezoelectric charge coefficient d₃₃ ≈ 296-360 pC N^-1 , converse piezoelectric coefficient ${\left(d_{33}^{\ast }\right)}_{\mathrm{ave}}$ ≈ 240-340 pm V^-1 , planar electromechanical coupling coefficient k_p ≈ 0.34-0.45, and electrostrictive coefficient (Q₃₃ )_avg ≈ 0.026-0.038 m⁴ C^-2 are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT-(0.4)BCST composition (x = 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead-free piezoelectric (1-x)BCZT-(x)BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1-x)BCZT-(x)BCST ceramics as a potentially strong contender within the family of Pb-free piezoelectric materials for future electronics and energy harvesting device technologies.

Keywords: electrostrictive coefficient; ferroelectric properties; lead-free piezoelectric; phase transition; piezoelectric coefficient.