Nonlinear Electrical And Optical Properties Of Perovskite Oxide Films

Perovskite oxides have been reported to be possessed of mulriple characteristics in electrics, optics, magnetics and calorifics due to its complexity of lattice structure. This material is expected to be widely used in next generation multi-functional electronic devices. In this dissertation, Samples of CaCu₃Ti₄O₁₂, Au: CaCu₃Ti₄O₁₂, Au: Ba0.6Sr0.4TiO3 single thin films and Pt/CaCu₃Ti₄O₁₂/ITO, In/CaCu₃Ti₄O₁₂/ITO and ITO/ CaCu₃Ti₄O₁₂/ITO multiple films were deposited on Nb: SrTiO3 (100) and MgO (100) substrates, respectively, by pulse laser deposition. The fabrication of perovskite oxide films and its nonlinear electrical and optical properties were studied, with emphasis on the pyroelectric properties of CaCu₃Ti₄O₁₂ films and enhanced nonlinear current-voltage behavior in Au: CaCu₃Ti₄O₁₂ films. The main results are listed as follows.1. The Au nanoparticle dispersed CaCu₃Ti₄O₁₂ films with different Au concentration were deposited on MgO (100) substrates by Pulse Laser Deposition. An enhanced nonlinear current-voltage behavior has been observed in these Au: CaCu₃Ti₄O₁₂ composite films. The double Schottky barrier model is used to explain the enhanced nonlinearity in I-V curves. According to the energy-band model and fitting result, the nonlinearity in Au: CaCu₃Ti₄O₁₂ film is mainly governed by thermionic emission in the reverse-biased Schottky barrier. This result not only supports the mechanism of double Schottky barrier in CaCu₃Ti₄O₁₂, but also indicates that the nonlinearity of current-voltage behavior could be improved in nano-metal composite films, which has great meaning for the resistance switching devices.2. CaCu₃Ti₄O₁₂ polycrystalline films with different thickness were fabricated on Nb:SrTiO3 (100) substrates. After being polarized, the pyroelectric coefficient was measured to be 1.35×10^-7 C/cm2K for the film with thickness of 700 nm from 295 K to 340 K, larger than those of most pyroelectric materials. It was observed that the pyroelectric coefficient increases with the thickness of films from 300 to 700 nm. The origin of pyroelectric effect is proposed to depend on the distortion of the Ti-O octahedron due to the presence of Ti³⁺ ions. Comparing with the measurement result of an unpolarized film, our study strongly supports the opinion of relaxor ferroelectric behavior in CaCu₃Ti₄O₁₂.3. Pyroelectric detector was made by using the CaCu₃Ti₄O₁₂ pyroelctric films, and the characteristics of pyroelectric signal were tested under the different biases. It was observed that the full width at half maximum of pyroelctric signal can be reduced under applied voltage, and the magnitude of signal could be enhanced or reduced by applying forward or reversed bias, respectively. These phenomena were analyzed based on the pyroelctric theory.4. Crystallized Au nanoparticle-dispersed Ba_0.6Sr_0.4TiO₃ thin films were prepared on MgO (100) substrates. The peak of linear absorption coefficient for the film shifts to longer wavelength with increase of Au concentration. Among all the tested samples, the largest values of third-order nonlinear susceptibility were calculated to be -1.93×10^-6 esu and 1.13×10^-5 esu responding to imaginary and real parts, respectively, which were determined by a single beam Z-scan at a wavelength of 532 nm with laser duration of 10 ns. The relationship between Au concentration and third-order nonlinear susceptibility was also analyzed.Highlights of the dissertation are as following:1. An enhanced nonlinear current-voltage behavior was observed in Au: CaCu₃Ti₄O₁₂ composite films. The conduction mechnism of Au: CaCu₃Ti₄O₁₂ film is analyzed by Double Schottky Barrier model. This result not only verifies the boundary effect in CCTO, but also indicates that the I-V nonlinearity could be improved by dispersing metal nanoparticles.2. The pyroelectric properties were discovered in CCTO films deposited on SNTO substrates. The pyroelectric coefficient was determined to be 1.35×10^-7 C/cm²Â·K, at least several times larger than that of most reported pyroelectric material. This result supports the opinion of relaxor ferroelectric in CCTO.3. The third-order nonlinear susceptibility of Au: Ba0.6Sr0.4TiO3 was determined to be 1.13×10^-5 esu by Z-scan method, at least one order larger than that of other composite films. The relationship between Au concentration and third-order nonlinear susceptibility was also analyzed...