Intermediate ferroelectric phase driven ferroelectric-relaxor crossover and superior storage properties in phase boundary engineered BCZT ceramics

Compositional tuning in materials at the morphotropic phase boundary has been a novel strategy to realize unprecedented and exotic physical properties. This work reports the structural, dielectric, electrical, and energy storage properties in lead-free BCZT (Ba0.85Ca0.15Zr0.1Ti0.9O3) at the morphotropic phase boundary (MPB) through compositional engineering at Ba-site. The polycrystalline samples of Ba0.85(1-x)(La1/2Na1/2)(0.85x)Ca0.15Zr0.1Ti0.9O3 (x = 0.0, 0.05, 0.075, 0.1) are synthesized by mechanical alloying followed by heating the samples at elevated temperatures. Rietveld refinement of powder X-ray diffraction patterns unveils coexisting ferroelectric P4mm (tetragonal) and ferroelectric R3m (Rhombohedral) symmetries, for samples x = 0.0-0.075. Intriguingly, the sample with x = 0.10 supports the inclusion of an intermediate ferroelectric phase with orthorhombic (Amm2) symmetry along with P4mm and R3m symmetries. Dielectric studies reveal a structurally coherent normal ferroelectric-ergodic relaxor crossover with Vogel-Fulcher type freezing of polar-nano-regions. Furthermore, the La/Na co-doping substantially enhances the recoverable energy density (W-rec); from 357 mJ/ cm(3) to 664 mJ/cm(3), reduces the loss energy density (W-L); from 101 mJ/cm(3) to 42 mJ/cm(3) and increases the storage efficiency (eta); from 77.9% to 94%. The doping-induced enhanced dielectric and storage properties are elucidated by impedance spectroscopy and density functional theory (DFT)-based calculations.

Automated summary

Compositional engineering at the morphotropic phase boundary is a strategy to achieve unprecedented physical properties. This study investigates the structural, dielectric, electrical, and energy storage properties of lead-free BCZT material through compositional tuning at the Ba-site. The addition of La/Na co-doping enhances the recoverable energy density, reduces the loss energy density, and increases the storage efficiency. The improved dielectric and storage properties are explained using impedance spectroscopy and density functional theory calculations.