Experimental And Theoretical Study On The Effect Of Temperature On Electrical Properties Of The BaTiO₃ Thin Films With Different Crystal Orientations

Ferroelectric thin films materials have attracted much attention,due to their excellent physical properties,including piezoelectric,pyroelectric,photoelectric,acousto-optic,nonlinear optical effects and high dielectric coefficients properties,which exhibited potential application prospects in many fields.In recent years,many researchs have shown that the properties of thin films can be regulated by changing various parameters.The crystal orientation of thin films is a key factor affecting their properties.And the investigation of the evolution process of domain switching under different field is one of the basic ways to understand the macroscopic piezoelectric properties of materials,and it is also the physical basis for understanding their storage properties.Therefore,BaTiO₃（BTO）ferroelectric thin films with different crystal orientations are selected as the research object in this paper.Firstly,the domain structure and piezoelectric properties of BTO thin films with different crystal orientations were investigated by piezoelectric force microscopy（PFM）,the domain state evolution and piezoelectric response of BTO thin films with different crystal orientations under temperature field were systematically investigated.Secondly,the single crystal polydomain model of（111）oriented ferroelectric thin film was deduced by nonlinear thermodynamics theory.The domain state evolution of（111）oriented BTO ferroelectric thin film at different temperature fields was investigated by the combination of experiment and theory.Finally,the relationship between dielectric piezoelectric properties and temperature of BTO thin films with different crystal orientations is analyzed.The main contents of this paper are as follows:1.BTO thin films were prepared by sol-gel method on（001）,（110）and（111）oriented Nb:SrTiO₃（N:STO）substrates.The microstructures of the films were characterized by X-ray diffraction（XRD）,X-rayΦscanning and Raman spectroscopy.The results show that the three BTO films not only inherit the out-of plane crystal orientation of STO substrates,but also arrange the in-plane crystal planes in an orderly manner.2.The out-of-plane and in-plane domain structures of BTO thin films with different orientations at nanoscale were investigated by PFM.The piezoelectric properties of three samples were characterized respectively.It is found that the domain structure and properties of films with different crystal orientation exhibit obvious anisotropy,and the differences of their properties are reasonably analyzed by experimental result.3.The domain state evolution of BTO thin films with different crystal orientations under temperature field was systematically investigated by using PFM,and the local piezoelectric response and ferroelectric switching behavior of thin films under different temperature were also recorded.At the same time,the domain state evolution mechanism of BTO（111）thin film under temperature was analyzed by combining the theoretical model of non-linear thermodynamics with the experimental results.4.The effects of temperature on the dielectric and piezoelectric properties of single crystal polydomain ferroelectric thin films were investigated by a nonlinear thermodynamic model of films with different crystal orientations.The relationship between temperature and dielectric piezoelectric coefficients of different crystal orientation films is obtained by numerical calculation.The results show that there are abrupt changes in properties at most temperature of domain transitions.