Preparation And And Properties Of BaTi₂O₅ Ferroelectric Thin Films By Sol-gel Method

BaTi₂O₅ material is a new lead-free ferroelectric material with a high Curie temperature,which can be applied in higher temperature environment.At present,the research on BaTi₂O₅ mainly focuses on single crystal,polycrystalline and ceramics.The research on BaTi₂O₅ thin films is not thorough enough,and the influencing factors of its phase transformation behavior are very complex,which needs further analysis.In this paper,BaTi₂O₅ films were prepared by Sol-gel method,and the optimal preparation processes were explored.The effects of Nb⁵⁺doping and Fe³⁺and Nb⁵⁺co-doping on the structure and properties of BaTi₂O₅ films were investigated.The broadening of Curie temperature region by different doping ions and the influencing factors of the phase change behavior were investigated.The details were as follows.1.The BaTi₂O₅ films were grown on Pt（111）/Ti/SiO₂/Si substrate by Sol-gel method.The effect of heat treatment process and the ratio of niobium-titanium ratio of the raw materials on the structure and electrical properties of the films was investigated,and the optimal processes for preparing BaTi₂O₅ films were obtained.It was found that the films prepared by the heating rate of 5℃/min had more uniform grain size and better electrical properties.The films prepared by using the raw material ratio of Ti:Ba of 2 had excellent electrical properties.2.The BaNb_xTi_2-xO₅（x=0,0.002,0.004,0.006,0.008,0.01）thin films were prepared on Pt（111）/Ti/SiO₂/Si substrates by Sol-gel method.The XRD and Raman results indicated that the BaNb_xTi_2-xO₅ thin films were in BaTi₂O₅ single phase,with no evidence of a secondary phase,and Nb⁵⁺ions were incorporated into the crystal lattice.Diffuse phase transition was observed in the films.The relationship between the dielectric constant and temperature of the film showed a wide platform and no frequency dependence.This widened platform was different from the sharp dielectric peak of a single crystal,which was a diffuse phase transition feature.In addition,the Nb⁵⁺doping could effectively improve the dielectric properties of BaNbxTi2-xO5 films and broaden the phase transition temperature region.As the Nb⁵⁺content increased,the Curie temperature decreased and a diffuse phase transition was observed for all films.For the film with x=0.006,an abnormally broadened dielectric platform was obtained in the temperature range of 200-400℃,and its value fluctuated in the range of 350±10.The research showed that the deformable monoclinic structure,fine grains,doping and thermal stress of BaTi₂O₅thin films contributed greatly to this abnormally broadened platform ofε（T）curve.In addition,with the increase of Nb⁵⁺content,the 2P_r increased first and then decreased.At x=0.004,the 2P_r of the film exhibited a maximum value of 0.8μC/cm² in the electric field of 175 kV/cm²,which was about four times that of the un-doped thin film（2P_r=0.2μC/cm²,x=0）.3.The effects of Fe³⁺and Nb⁵⁺co-doping on the structure and properties of BaTi₂O₅ films were investigated.The effects of donor and acceptor ion doping on the phase transition behavior of the films were analyzed.Combined with XRD and Raman results,all BaFe_xNb_xTi_2-2xO₅（x=0,0.004,0.006,0.008）films were in BaTi₂O₅ single phase and the doped ions were incorporated into the crystal lattice.The dielectric properties of the films were effectively improved by co-doping Fe³⁺and Nb⁵⁺.For the film with x=0.004,it was found that theε（T）curve exhibited a broad dielectric platform at T_m,which was still a diffuse phase transition.Theγvalue of the dispersion degree was calculated by Curie’s law,and it was found that the co-doped Fe³⁺and Nb⁵⁺ions increased the diffusion degree of the films and expanded the phase transition temperature region.In addition,suitable amounts of Fe³⁺and Nb⁵⁺were also effectively improve the ferroelectric properties of BaTi₂O₅films.