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.