Ferroelectric and piezoelectric enhancement in lead-free NaNbO₃–BiErKZrO₃ perovskite ceramics: Tetragonal phase stability and optical properties

Abstract

Lead-free (1-x)NaNbO₃-xBiErKZrO₃ (x = 0.01, 0.02, 0.03, and 0.04 mol%) ceramics were synthesized using a three-step solid-state sintering method, exhibiting a stable tetragonal perovskite structure (P4/mbm), as confirmed by X-ray diffraction (XRD) and Rietveld refinement. Raman spectroscopy verified the presence of NbO₆ octahedral vibrational modes, ensuring structural stability. Microstructural analysis via FE-SEM and HR-TEM revealed homogeneously distributed grains with low defect concentrations, contributing to enhanced densification and electrical uniformity. The optical characterization demonstrated a tunable bandgap between 3.21 and 3.27 eV, making these ceramics suitable for optoelectronic applications. Photoluminescence (PL) spectra exhibited intense emissions at 597 and 640 nm, with a high color purity of 85 % and a correlated color temperature (CCT) of 2088 K, indicating potential for display and lighting technologies. Dielectric studies revealed a broad ferroelectric-to-paraelectric transition occurring between 120°C and 250°C, with strong frequency-dependent permittivity. Ferroelectric analysis indicated that the x = 0.02 composition achieved optimal performance, with a remanent polarization (Pᵣ) of 4.9378 μC/cm² and a dielectric energy density of 12.3445 μJ/cm³ , suggesting its potential for high-energy storage applications. Piezoelectric measurements showed enhanced properties at x = 0.03, where the piezoelectric coefficients d₃₃, d₃₂, and d₃₁ were recorded as 156, 144, and 143 pC/N, respectively. The voltage coefficient (g₃₃) reached 69.032 × 10⁻¹ ⁵ V·m/N, and the figure of merit (d₃₃ × g₃₃) was calculated as 10.7680 × 10⁻³ ⁰ J/m³ . Mechanical stability was supported by a mechanical quality factor (Qₘ) of 20 and an acoustic impedance of approximately 24,600 kg/m²s. These findings highlight the multifunctionality of (1-x)NaNbO₃-xBiErKZrO₃ ceramics, demonstrating their suitability for advanced applications in energy storage, piezoelectric transducers, optoelectronic devices, and next-generation microelectronic components.