Tuning of the electrocaloric effect over a broad temperature range by vacancy-induced disorder in the lead-free ferroelectric system

Abstract Searching for material with a high electrocaloric (EC) response over a wide temperature range near the ambient temperature is a priority area of research in solid-state refrigeration technology. The perovskite system with cationic vacancies could allow tuning the EC parameters over a wide temperature range via the associated entropy change. In this context, La-substituted BaTiO 3 has been investigated, with a focus on introducing cationic vacancies to dilute the ferroelectric system with a primary objective of simultaneously tailoring the Curie temperature ( T C ) closer to room temperature (∼300 K) and stabilizing it over a wide temperature span. The analysis of Raman and x-ray photoelectron spectroscopy confirms the formation of cationic vacancies. Consequently, a diffused ferroelectric phase transition with weak relaxor feature is confirmed by modified-Curie–Weiss law and Vogel–Fulcher fitting analysis. As a result, the observed shift in ferroelectric transition temperature from 400 K to 290 K upon La-substitution is correlated to the effect of vacancies in the perovskite structure. In addition, the EC studies demonstrated the tuning of adiabatic temperature change ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> </mml:mrow> </mml:mrow> </mml:math> T ) spanning over a wide temperature range ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>span</mml:mtext> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) from 5 K to 45 K, covering the room temperature. Tuning of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>span</mml:mtext> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> with a moderate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Δ</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>max</mml:mtext> </mml:mrow> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> values highlight the La-substituted sample’s potential in cooling applications with relative cooling power values ranging from 34.92 K 2 to 67.58 K 2 . These studies provide insights into tuning the EC parameters by inducing cationic vacancies in the perovskite-based ferroelectric oxides.