| is a kind of novel thermoelectric oxide material which has been used for potential applications at mid or high temperature. The crystal structure of Ca3Co4O9is a monoclinic misfit-layered structure consisting of stacks of two-dimensional conductive CoO2planes and insulating Ca2CoO3layers along the c-axis. This type of misfit-layered structure has the characteristic of "electronic crystal-phonon glass" and significant anisotropy with large space of modified thermoelectric properties. Systematical research about Ca3Co4O9polycrystals and their thin films, as well as the laser-induced voltage (LTV) effect of was made in this thesis. From which we got aware of the proper growth condition, electrical transport properties and laser-induced voltage performance of the epitaxial films grown on the substrates of flat and tilted LaA103(LAO) and the physical mechanism of intrinsic anisotropy that generates voltage signals, as well as the influences of some extrinsic factors were also discussed. Furthermore, the polycrystalline bulks and films with doped Cuã€Bi and the influence of dopping ratio on the electrical properties and anisoropy were also investigated.The highly c-axis oriented polycrystalline Ca3Co4O9, Ca3Co4-xCuxO9(x=0.05～0.5) and Ca3-xBixCo4O9(x=0.05-0.5) bulks were prepared by the optimum solid-state reaction process (800℃/24h+870℃/24h), which was obtained via the references of thermoanalysis. Four-probe measurement of R-T curve(80K-300K) has been used to analyze the electrical transport properties of polycrystal and it turned out that these three series of polycrystal all showed metal transport behaviors. The influence on grain growth, orientation and electrical transport properties of Cun Bi doping ratio have been investigated at the same time. By constructing the chamfered surface of the polycrystalline bulk, we achieved laser induced voltage effect (LIV) in the (00/) oriented Ca3Co4O9polycrystal for the first time, the anisotropy of polycrystalline grains are the main causes of the LIV signal.Pulsed laser deposition technology (PLD) was employed to grow Ca3Co4O9films on the flat and tilted monocrystal LAO substrates. The XRD results showed that the epitaxial-featured films were prepared successfully. The AFM showed the obvious differences of grain arrangements on the flat and tilted substrates. The R-T curves of80K～300K suggested that films grown on the flat substrates were characterized with obvious metal behaviors. While, the films on the tilted substrates showed semi-conductive behaviors and their resistivity had a directly propotional dependence on the angle of inclination.248nm pulsed laser was used as the heating source to heat upper surface. Through which we explored the LIV effects of Ca3Co4O9films grown on the tilted substrates, and the influences of intrinsic anisotropy, growth temperature, laser energy density, angle of inclination and the frequency of pulse laser bombardment on the LIV signal of Ca3Co4O9films were also investigated. The peak signal of LIV rised first, and then dropped along with the temperature, it reached a maximum of352mV at780℃, which proved linear positive correlation with laser energy density. According to XRD and LIV signals that came from the films grew on tilted substrates with angles of10°and15°, it showed there is no epitaxial growth on the substrates of10°and15°, this causes a low voltage signal. Peak signals dropped as the increasing frequency of pulse laser bombardment.The electronic transmission properties and LIV of films that doped with Cu Ca3Co4-xCuxO9(x=0.15,0.3) were also studied. However, the LIV peak signal of Cu doped film is lower than that without any doping, and has decreased anisotropy. |
