The Bi <sub> 2 </ Sub> A <sub> 2 </ Sub> The Co. <sub> 2 </ Sub> O <sub> Y </ Sub> (a = Ca, Sr, Ba) System Thermoelectric Thin Films The Litv Effects And Electrical Transport Properties Of Study

Laser induced thermoelectric voltage (LITV) effect was observed on these Bi2Ca2Co2Oy, Bi2Ba2Co2Oy thermoelectric thin films grown on vicinal-cut single crystalline substrates for the first time. Film thermal diffusivity and anisotropy of the Seebeck coefficient of the signal were studied by fitting the data LITV and mismatch performances of their thermoelectric properties with LITV signals were analyzed.The Bi2Ca2Co2Oy, Bi2Sr2Co2Oy, and Bi2Ba2Co2Oy polycrystalline ceramics were prepared by solid state reaction as thin film deposition targets. Their structures were analysised by X-ray diffraction (XRD), the results showed that these prepared targets were single phase with c-axis preferred orientation of polycrystalline ceramics, we employed resistance & temperature behaviors techniques to investigate electric properties of these targets.The data showed that Bi2Ca2Co2Oy showed semiconducting properties in the measured temperature range.For Bi2Sr2Co2Oy, there is a phenomenon of semiconducting to metal conductivity transition at a certain temperature and Bi2Ba2Co2Oy was metallic electrical properties. The semiconductor behavior of the targets was investigated under the formula to the resistivity-temperature curve, and the semiconductor conductive thermal activation model was employed of to calculate the thermal activation energy. Analysis showed that the conductivity of polycrystalline layers becomed better with the lower of the mismatch.The Bi2Ca2Co2Oy, Bi2Sr2Co2Oy, Bi2Ba2Co2Oy films were prepared by pulsed laser deposition (PLD) on the Al2O3 single crystal substrates. We discussed the influence of different growth conditions on structure, properties of these thin films, such as temperature, oxygen pressure and other parameters. X-ray diffraction (XRD) analysis showed that they all have a high degree of c-axis orientation. Resistance & temperature behaviors techniques were measured by four probe method. The results indicated that there were a semiconducting to metal conductivity transition temperature for Bi2Ca2Co2Oy and Bi2Sr2Co2Oy, but Bi2Ba2Co2Oy shows metallic electrical properties. Conductivity of films were analyzed with the change of lattice mismatch, And a simple comparison and analysis were done in the electrical transport properties between films and polycrystalline. The three series of thermoelectric thin films were grown on the 10°vicinal-cut Al2O3 single crystal substrates, and the LITV signals were observed on all these films. The thickness was studied to investigate the influence on the LITV signals. The results show that there is an optimum film thickness to the maximum LITV signal. Mismatch between layers impacting on the LITV signal was also studied, and shows that when the mismatch between layers was the greater, the LITV signal was greater too.The relationship between film thermal diffusivity D and film thickness was obtained by fitting the parameters LITV signal fall time, according to one-dimensional heat conduction model we derived the temperature between upper and lower surface of the film, A new formula with anisotropic Seebeck coefficient (Sab-Sc) was pushed through reported in the literature combined with laser induced thermoelectric voltage formula. These were calculated according to the findings and measurement of the film LITV signal to that the thermal diffusivity of films D and Sab-Sc. It was analysised that D and Sab-Sc with the mismatch between layers changes in relations. D is from increase to decrease with the the increase of mismatch between layers, and Sab-Sc is always decrease with that, On the other hand it also shows that the material which have a larger Seebeck coefficient also have a larger anisotropy of Seebeck coefficient, and vice versa.According to the above conclusions, a new method for rapid assessment of the thermoelectric properties of materials has been proposed. Namely:determining anisotropy Seebeck coefficient (Sab-Sc) can rely on measuring the peak level of its LITV signal, whereas (Sab-Sc) of its large Seebeck coefficient of the material must be greater; The thermal diffusion coefficient can be estimated by fitting the falling edge of the signal time LITV, and thus to compare the size of the thermal conductivity; It may be inferred that the merits of their electrical transport properties by four-probe measurement of R-T relationships. There for,we can determine the three important parameters which affect the value of thermoelectric materials, in turn, can compare the thermoelectric properties of a good or bad.