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

BaTi₂O₅ material is a promising candidate for a new lead-free ferroelectric material at high temperature,exhibiting high dielectric permittivity（εr）and low dielectric loss（tanδ）at a high Curie temperature（T_c）.The research on the BaTi₂O₅system was focused on the single-crystalline,（010）oriented polycrystalline and polycrystalline BaTi₂O₅.However,no systematic studies are available for the BaTi₂O₅ thin film.Due to the miniaturization and integration,BaTi₂O₅ should be applied as the form of film,which exhibites smaller size than that of bulks.Therefore,the investigation of the properties and structure of the BaTi₂O₅ thin film is enssential for its application.1.The BaTi₂O₅ thin films were prepared on Pt（111）/Ti/SiO₂/Si substrates via sol-gel process.The optimized temperature and time of annealing process were obtained.The well crystallized BaTi₂O₅ thin films were obtained at 800–900°C.The BaTi₂O₅ thin films annealed at 850°C for 30 min had the maximum dielectric permittivity of 210.The dielectric properties of the BaTi₂O₅ thin film were investigated using temperature dependent dielectric measurements in conjunction with temperature dependent Raman spectra.Diffuse phase transition was found in BaTi2O5 thin film which exhibited a broad peak without frequency dependence on theεversus T,ε（T）,curves around 370°C.2.The BaFe_xTi_2-xO₅（x=0,0.004,0.008,0.012）thin films were prepared on Pt（111）/Ti/SiO₂/Si substrates via sol-gel process and annealed at 850°C for 30 min.The XRD and Raman results indicated that the BaFexTi2-xO5 thin films were in BaTi₂O₅ single phase,with no evidence of a secondary phase.With increasing Fe³⁺content,theεr at room temperature increased and showed the highest value of dielectric permittivity（εr=680）at x=0.004,which was about 3 times higher than that of the film with x=0（ε_r=210）.As the Fe³⁺content was more than 0.004,theε_r decreased slightly.Comparing with the dielectric peak of the BaTi₂O₅ thin films around 370°C,theε（T）curves of Fe-doped BaTi₂O₅ thin films exhibited near-plateau dielectric permittivity maximum with weak frequency dependency in wide temperature ranges.For the thin film with x=0.012,the dielectric permittivity value was 845+10 in the temperature range of 150-340°C.3.BaZr_x Ti_2-xO₅（x=0,0.002,0.004,0.008）thin films were successfully deposited on Pt（111）/Ti/SiO₂/Si substrates via sol-gel process and annealed at850°C for 30 min.The XRD and Raman results indicated that the BaZrxTi2-xO5 thin films were in BaTi₂O₅ single phase,with no evidence of a secondary phase.With increasing Zr⁴⁺content,theε_r at room temperature increased and showed the highest value of dielectric permittivity（ε_r=440）at x=0.004.As the Zr⁴⁺content was more than 0.004,theε_r decreased slightly.Diffuse phase transition was observed in both BaZrxTi2-xO5 thin films with x=0 and x=0.004.The dielectric permittivity peaks were analyzed by the modified Curie-Weiss law.The results revealed that the diffuse degree of the BaTi₂O₅ thin films was increased by Zr⁴⁺substitution.