Preparation And Properties Of Ba_0.3Sr_0.7TiO₃ Microcrystalline Thin Films For Energy Storage Application

The demand for energy is increasing rapidly,so energy storage becomes an important part of modern energy supply chain.In the current energy storage materials,choosing materials with high polarizability,moderate dielectric constant,small leakage current,strong energy storage capacity and stable chemical properties is the key to improve energy storage performance.In this work,Ba_0.3Sr_0.7TiO₃?BST?material was selected to prepare the films by sol-gel method with a spin-coating process on Pt/Ti/SiO2/Si substrate and baked.After repeating the above steps several times,the BST microcrystalline film was obtained by one-step annealing.The effects of annealing temperature,annealing time and film thickness on the internal structure,microstructure,energy storage and dielectric properties of Ba_0.3Sr_0.7TiO₃ microcrystalline films were studied.Firstly,crystal growth process of the film could be controlled by regulating the annealing temperature.When the annealing temperature is 700 ^oC,BST crystallite film was prepared with energy storage density of 31.56 J/cm³ at 2.96 MV/cm.The increase of annealing temperature improve the crystallization of the film,and the grain size of the film increased from 2 nm to 20 nm.The surface of the film gradually became rough with a small number of pores and other defects.The breakdown strength and the energy storage density of the films first increased slightly and then decreased sharply with the increase of temperature.At 700 ^oC,the film obtained the optimal energy storage performance,while BST crystallite film existed in a mixture state of crystalline and amorphous.There is a great deal of amorphous state in the film,and the amorphous are connected to form a three-dimensional network structure with the tiny BST grains wrapped.The dielectric constant and dielectric loss of the film reach to the minimum 60 and 0.001 at the same time.Then the optimal annealing temperature was determined,and the annealing time is regulated.With the increase of annealing time,the crystallinity and the roughness of the films increase obviously.If the crystallization time is too long,the grains will occur agglomeration resulting in abnormal growth,which is very adverse to the dielectric and energy storage properties of the films.Therefore,with the increase of annealing time,the energy storage density and the breakdown strength of the thin film decrease intensely,and the dielectric constant and dielectric loss increase.When annealing for 60 s,the optimal BST microcrystalline thin film was obtained with a breakdown field strength of 4.48 MV/cm and an energy storage density of28.77 J/cm³.Finally,the thickness of the film is controlled by the number of coating layers?2-10?.The BST microcrystalline films with a thickness of 42-74 nm were obtained.Since the increase of the thickness,the less heat absorbed by per unit volume of the film during heat treatment,so smaller thermal fluctuation inside the film causes the smaller size and quantity of nucleation.Thus the crystallinity of the film decreases with the increase of the thickness.When the thickness was between 42 nm and 68 nm,the breakdown strength of the film increased from 2.77 MV/cm to 14.19 MV/cm,and the effective energy storage density increased from 11.18 J/cm³ to 89.94 J/cm³,so the excellent dielectric with high energy storage potential was obtained.