Mechanism of enhanced energy storage density in AgNbO3-based lead-free antiferroelectrics

Abstract

The mechanisms underpinning high energy storage density in lead-free Ag 1–3 x Nd x Ta y Nb 1- y O 3 antiferroelectric (AFE) ceramics have been investigated. Rietveld refinements of in-situ synchrotron X-ray data reveal that the structure remains quadrupled and orthorhombic under electric field ( E ) but adopts a non-centrosymmetric space group, Pmc2 1 , in which the cations exhibit a ferrielectric configuration. Nd and Ta doping both stabilize the AFE structure, thereby increasing the AFE-ferrielectric switching field from 150 to 350 kV cm −1 . Domain size and correlation length of AFE/ferrielectric coupling reduce with Nd doping, leading to slimmer hysteresis loops. The maximum polarization (P max ) is optimized through A-site aliovalent doping which also decreases electrical conductivity, permitting the application of a larger E . These effects combine to enhance energy storage density to give W rec = 6.5 J cm −3 for Ag 0.97 Nd 0.01 Ta 0.20 Nb 0.80 O 3 . Schematic diagram illustrating how energy storage density is optimized through doping in AgNbO 3 and shedding light on the design of novel antiferroelectric (AFE) materials with excellent energy storage density. ● Excellent performance achieved for AgNbO 3 -based antiferroelectric lead-free energy storage ceramics. ● The first observation of a field induced ferrielectric phase. ● 4 principles proposed for the design of high energy density properties of AgNbO 3 -based antiferroelectric ceramics: i) increased resistivity, ii) optimization of maximum polarization, iii) decreased antipolar/polar coupling, and iv) enhanced AFE stability.