| Perovskite-type Sr Ti O3 is expected to be one of the high temperature n-type thermoelectric materials for industrial application. However, its thermal conductivity is very high and its electrical conductivity decreases with increasing temperatures, resulting in the low thermoelectric performance of Sr Ti O3. In this paper, in order to improve the thermoelectric properties of Sr Ti O3-based materials, the ways that La and Dy co-doped in Sr Ti O3 materials to enhance its electrical conductivity and Sr Ti O3 fibers added to reduce the thermal conductivity were used.In this paper, the sol-gel method was used to prepare the La and Dy co-doped Sr Ti O3 powder. Sr Ti O3 fibers were synthesized through the hydrothermal method. Then, the influencing mechanism of the La, Dy and Sr ratio and Sr Ti O3 fiber for phase composition, structure and sintering properties of Sr Ti O3 ceramics were investigated. What is more, the electrical conductivity, Seebeck coefficient, thermal conductivity and ZT value were studied from 50°C up to 500°C.First, effects of Sr content on structure and thermoelectric performance of La0.1Dy0.1Sr1-0.2y Ti O3(y = 1, 1.1, 1.25, 1.25) series ceramics were studied. The results showed that the electrical conductivity was significantly enhanced, and the Seebeck coefficient was slightly reduced, while the thermal conductivity was increased, with the decrease of Sr content. The thermoelectric properties of sample with y=1.25 is best. Its power factor reaches the maximum value 997μW·m-1·K-2 at 200°C, and its ZT value is 0.19 at 500°C. At the same time, the step morphology was observed in lower Sr content samples, and their formation mechanism was discussed.Secondly, effects of Dy doping for structure and thermoelectric performance of the La0.1Dyx Sr1-1.25(0.1+x)Ti O3 series ceramic were discussed. The results indicated that Dy2Ti2O7 phase appeared in the samples and the grain size reduced to about 5μm with the increase of Dy doping amount. In addition, the electrical conductivity and Seebeck coefficient increases at the same time, while the thermal conductivity is significantly reduced with the increase of the Dy doping amount, resulting in the ZT value of sample with x = 0.1 reaching 0.29 at 500°C, which is the three times larger than that of sample with x=0.Finally, the influence of the hydrothermal temperature and time, the Sr2+ concentration and ratio of Sr and Ti in the precursor solution on the composition and morphology of Sr Ti O3 fiber was investigated. Then, Sr Ti O3 fiber/La and Dy co-doped Sr Ti O3-based ceramics were prepared. The optimum preparation process conditions of Sr Ti O3 fiber are as follows: the hydrothermal temperature is 180°C, hydrothermal time is 48 h, the Sr2+ concentration is 15mmol/L and the ratio of Sr and Ti is 10:1. The sintering temperature of ceramics with Sr Ti O3 fiber can be reduced 100°C. In addition, the electrical conductivity is enhanced and the Seebeck coefficient is only a little changed, while the thermal conductivity decreases with adding Sr Ti O3 fiber. By adding 3.0mass% Sr Ti O3 fiber and sintering at 1450°C, the power factor can reach to 1014μW·m-1·K-2 at 200°C, which is about 14 times larger than that of sample without fibers; the ZT value can reach 0.19 at 500°C, which is 4.75 times larger than that of sample without fibers. |
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