Direct and Indirect methods of electrocaloric effect determination and energy storage calculation in (Na0.8K0.2)0.5Bi0.5TiO3 ceramic

TL;DR

This study investigates the electrocaloric effect and energy storage capacity of lead-free NKBT ceramic using direct and indirect methods, revealing significant temperature change and high energy density near phase transition points.

Contribution

It provides comprehensive analysis of NKBT ceramic's electrocaloric and energy storage properties through combined structural, dielectric, and measurement techniques, highlighting its multifunctionality.

Findings

Electrocaloric temperature change ~ 1.10 K at 20 kV/cm

Maximum recoverable energy ~ 0.78 J/cm3 at 423 K

Electrical storage efficiency ~ 86% at optimal conditions

Abstract

The coexistence of multiple structural phases and field induced short-range to long-range order transition in ferroelectric materials, leads to a strong electrocaloric effect (ECE) and electrical energy storage density (Wrec) in the vicinity of ferroelectric to non-ergodic phase transition in NKBT ceramic. Structural analysis using X-ray diffraction, Raman spectroscopy and TEM studies ascertained the coexistence of tetragonal (P4mm) and rhombohedral (R3c) phases. Dielectric study has revealed a critical slowing down of polar domain dynamics below a diffuse phase transition. Present investigation reports ECE in lead-free (Na0.8K0.2)0.5Bi0.5TiO3 (NKBT) ceramic by direct and indirect methods, which confirm the multifunctional nature of NKBT and its usefulness for applications in refrigeration and energy storage. A direct method of EC measurement in NKBT ceramic exhibits significant adiabatic temperature change ({\Delta}T) ~ 1.10 K and electrocaloric strength ({\xi}) ~ 0.55 Kmm/kV near the ferroelectric to non-ergodic phase transition at an external applied field of 20 kV/cm. A highest recoverable energy (Wrec) ~ 0.78 J/cm3 and electrical storage efficiency ({\eta}) ~ 86% are achieved at 423 K and an applied field of 20 kV/cm. This behavior is ascribed to the delicate balance between the field induced order-disordered transition and the thermal energy needed to disrupt field induced co-operative interaction.