Study On Ferroelectric And Piezoelectric Properties Of Tb-doped?BaCa??Zr Ti?O₃ Ceramic Blocks And Films

The piezoelectric ceramics and thin films have developed rapidly in recent year as one of important functional materials,which can be used to prepare sensors,actuators,resonators and other electronic components.And the applications involve military communications,aerospace,signal processing and many other high-tech fields.Though the traditional lead-containing ceramics possess excellent properties,the lead is a volatile toxic element which is harmful to environment and human health.In order to meet the needs of sustainable development,it is imperative to develop environmentally friendly lead-free ceramics with excellent properties.The?BaCa??ZrTi?O₃ based lead-free ceramics are considered as one of the most potential substitutes for lead-containing materials because of their high relative dielectric constant??_r?,residual polarization strength?P_r?,low dielectric loss and excellent piezoelectric properties which is comparable to that of Pb(Zr_1-x-x Ti_x)O₃?PZT?.However,the high sintering temperature?usually>1500??,low Curie temperature?T_c?90??and strong temperature-dependence in electrical properties of?BaCa??ZrTi?O₃hamper their practical applications.In addition,with the development of microelectronics industry,the preparation of high-performance lead-free piezoelectric thin film materials can meet the market demand for miniaturization and high integration of electronic components.It is a research hotspot in the field of lead-free piezoelectric materials and has important practical significance.Accordingly,in view of these problems above in?BaCa??ZrTi?O₃ system materials,this paper studies the improvement of piezoelectric,ferroelectric and sintering properties of ceramics by ion doping and liquid-phase sintering method,and the physical and chemical mechanisms of improved properties in materials have been analyzed.Moreover,the preparation conditions of high-performance piezoelectric thin film materials have been explored.The effects of doping,buffer layer and annealing treatment on the structure and properties of?BaCa??ZrTi?O₃ thin films have been studied,which have important scientific significance and practical values for the development of lead-free materials in this system.The Tb₄O₇ was used to adjust the phase structure of?BaCa??ZrTi?O₃ for improving its piezoelectric properties and ferroelectric temperature stabilities.And x mol%?x=0.1⁰.5?Tb-doped 0.47(Ba_0.7Ca_0.3)TiO₃-0.53Ba(Zr_0.2Ti_0.8)O₃?BCZT-x Tb?piezoelectric ceramics were fabricated by conventional solid state reaction method.The phase transformation,dielectric,ferroelectric and piezoelectric properties of BCZT-x Tb ceramics were studied.Tb has two valence states,which Tb³⁺can occupy the A site and Tb⁴⁺occupies the B site in the ABO₃structure of ceramics.And the introduction of Tb can reduce the phase transition temperature between orthogonal phase and tetragonal phase(T_O-T)in ceramics.The 0.2 mol%Tb-doped sample possesses the best ferroelectric and piezoelectric properties at room temperature.When Tb doping concentration is greater than 0.3mol%,the ferroelectric maximum deviation?d P_r?_M⁺of ceramics can be reduced in the 20⁹0?,which indicates the temperature stability of ferroelectric properties in ceramics are improved.The CaCl₂ was added in 0.2 mol%Tb doped BCZT as sintering aid.The effects of sintering temperature and doping concentration of CaCl₂ on the structure,morphology,dielectric,ferroelectric and piezoelectric properties of the ceramics were studied systematically.It is found that the density,piezoelectric and ferroelectric properties of the ceramics could be significantly improved by appropriate CaCl₂ doping at various sintering temperatures.At 1410?sintered,the relative density of 0.2 mol%Tb and 0.2 wt%CaCl₂ co-doped sample is 96%,and the residual polarization P_r and piezoelectric coefficient d₃₃*of sample can reach 11.4?C/cm² and 720 pm/V,which are about 39%and 32%higher than those of pure BCZT,respectively.The dielectric temperature relationship measurements show that the Curie point temperature T_C of the ceramics can be increased about 10?by adding 0.1⁰.3 wt%CaCl₂,which broadens the application temperature range of the ceramics.A series of ceramic targets of BCZT-x Tb were prepared by the conventional solid-state reaction technique.Then,BCZT-x Tb thin films were prepared on Pt/Si substrates by PLD technique.The effects of Tb₄O₇ introduction on the structure and properties of the films were investigated.The results show that Tb doping can increase the crystallization degree and grain size,decrease the leakage current density and improve the ferroelectric and piezoelectric properties of the films.The 0.4 mol%Tb doped film possess the best comprehensive properties.Comparing with pure BCZT film,the residual polarization?P_r?of 0.4 mol%Tb-doped film increase from 3.6 to 6.4?C/cm²,d₃₃*increase from 52 to 63 pm/V.And the leakage current density value of 0.4 mol%Tb doped film is about one order of magnitude smaller than that of pure BCZT film.Then,these films were annealed at different temperatures to study the effects of annealing treatment on the structure and properties of films.The results show that the BCZT-0.4Tb film annealed at 800?for 3 hours possess the best ferroelectric and piezoelectric properties,which P_r,E_c and d₃₃*of specimen are 9.8?C/cm²,26.6 kV/cm and 74pm/V,respectively.The SrTiO₃?STO?about 200 nm was grown on Pt?111?/Si substrate as buffer layer by PLD technique,and then BCZT-0.4Tb/STO/Pt?111?/Si ferroelectric thin film was prepared,and the electrical properties of film was studied.The variations of dielectric and ferroelectric properties of the film were discussed,and the meachanisms of improved properties were analysed.It is found that the buffer layer can promote the grain growth,increase?100?orientation and improve the ferroelectric properties of the film.The P_r value of the film with buffer layer is 9.0?C/cm²,which is about 40%higher than that of the film without buffer layer.