| Thermoelectric materials are functional materials which can convert heat energy to electric energy directly due to thermoelectric effects and have immense prospects with many applications in thermoelectric power generation and refrigeration.The single crystal of the new oxide thermoelectric materials,Ca3Co4O9 exhibits good thermoelectric properties, which make this compound as a promising candidate for application to power generators.But single crystal is too expensive in its synthetic and the ZT value of polycrystalline is low.Therefore making good thermoelectric performance Ca3Co4O9 materials is the key that this material can apply extensively.Compared with bulk thermoelectric materials,oxide thermoelectric thin film is a new research field.To increase the thermoelectric performance of the materials,decreasing the dimensions of the thermoelectric materials is a effective path.There are many advantages for oxide thermoelectric thin film,such as high serviceability temperature,low pollution,oxidation resistant and long operating life.In this dissertation,Ca(NO3)2·4H2O, Co(NO3)2·6H2O were used as raw materials,ethylene alcohol as solvent, citrate acid as chelator.The Ca3Co4O9 polycrystalline was synthesized by polymerized complex(PC)method.The Ca3Co4O9 thin film was deposited on Al2O3(0001)substrate successfully by pulse laser deposition.The Ca3Co4O9 polycrystalline targets were analyzed by XRD scattering and SEM microscope.In XRD patterns,there is no other diffraction peaks except Ca3Co4O9 phase peaks,indicating that PC method can synthesize single-phase Ca3Co4O9 polycrystalline targets,experiment results show that the better sintering temperature of Ca3Co4O9 is 880℃,and its better holding time is 2 hours.Metallography microscope images show that the samples' crystalline grain size with long holding time are not uniform,and the grain size of samples with 2h holding time is smaller and distribute more homogeneous.In this paper the growth condition of Ca3Co4O9 thin film deposited by PLD was discussed.The orientation of the films was analyzed by XRD scattering,XRD patterns show that the Ca3Co4O9 thin films deposited on Al2O3(0001)substrate are single phase,all highly c-axis orientation and crystallize well.The experiments results show that the temperature of the substrate has big influence on the growth of the films,higher temperature can help the film release its internal stress.The surface of the thin film is very smooth.The electric resistance of the thin film is low and it goes up with the temperature,the film has obvious semi-conductor characteristic. |
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