High Electrocaloric Effect In Hot-pressed PLZT Ceramics With Wide Operating Temperature Range

The refrigeration technology based on electrocaloric effect?ECE?has many advantages such as high power efficiency,high reliability,low cost,small size and environmental protection,compared to other refrigeration technologies,which proves its full potential to be applied in cooling devices in the future.The ECE materials which has been widely studied today have their own advantages and disadvantages respectively.Among them,conventional sintering ceramics have high cooling efficiency and low cost but also low breakdown strength and low stability among wide operating temperature range which limit the ECE properties of them and restrict the application for daily life.So it is of great significance to solve these problems for applying these materials.The paper will introduce the improvements of relaxor ferroelectric Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics by hot-press sintering on temperature stability,dielectric properties and ECE properties.This method effectively handled the problems in conventional sintering ceramics we mentioned above.Small grain size,high density,low porosity and high diffusion constant?are all necessary for stability among wide operating temperature range in ceramics.When Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics with 0-10 mol%excess PbO were sintered by the conventional and hot-pressing processes,respectively.The grain size,relative density and?of hot-pressed samples are 2-3?m,>95%and 1.83-1.89 respectively with low volatility.As for conventional samples,they are 2-5?m,90%-95%and 1.65-1.82 respectively with high volatility.These prove hot-press sintering can improve the stability among wide operating temperature range in Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics.High breakdown strength and high resistivity are requirements for enhancing ECE properties of ceramics.When the samples mentioned above were tested between 0-100?,the breakdown strength and resistivity of the hot-pressed samples are beyond 200KV/cm and beyond 10¹³?m respectively,while which of the conventional ones are around100KV/cm and around 10¹¹?m respectively.These prove hot-press sintering can increase the breakdown strength of Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics in wide operating temperature range which leads to better ECE properties of Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics in wide operating temperature rangeadiabatic temperature change?T,isothermal entropy change?S and their instabilities are common measurements for ECE properties of materials.High?T,high?S and low instabilities prove great ECE properties.When the samples mentioned above were tested between 0-100?with 100KV/cm applied electric field.?T,?S and their instabilities of the hot-pressed samples are 1.3-2.4?,1.5-2.3 J kg^-1 K^-11 and around 20%respectively,while which of the conventional ones are 0.5-1.9?,0.6-1.9 J kg^-1 K^-1 and around 40%.In addition,when applied electric field increased to 200KV/cm,?T,?S and their instabilities of the hot-pressed samples are 2.2-3.4?,2.5-3.2 J kg^-1 K^-11 and around20%respectively.These prove hot-press sintering can advance ECE properties and stability of Pb_0.85La_0.1(Zr_0.65Ti_0.35)O₃ ceramics in wide operating temperature range.