Investigation On The Thermoelectric Properties Of Nb-doped TiO₂

With the development of human society,non-renewable energy resources such as coal,oil,natural gas are becoming less and less,in addition,global warming,an expansion of desert area and a rise in sea level occur with the use of these energy,which makes the exploration and development of new energy become increasingly important.However,if one want to really use the new energy,the new energy materials must be employed.Thermoelectric material belongs to a kind of new energy materials.But,so far,the thermoelectric energy conversion technology failed to completely replace the traditional power generation technology,and simply served as an effective complement of the conventional power generation technology.The biggest challenge that thermoelectric material faced is that the energy conversion efficiency has not reached the demand of practical application.In order to make the thermoelctric material widely used,researchers attempt to improve the thermoelectric performance of materials by doping.This paper selected the oxide semiconductor thermoelectric material TiO₂ as the research object,and doping by Nb element,following different heat treatment condition,and finally investigated the thermoelectric performance of this series of samples.The concrete contents of this study are as follows:1.A series of Nb-doped TiO₂-?(Ti_1-xNb_xO₂-d)ceramics was fabricated using a conventional solid state reaction method with subsequent annealing in an atmosphere of mixed H2 and Ar.X-ray diffraction revealed that there are different phases in the ceramics with different Nb doping levels,x.It may be seen that the x = 0.0,0.005,0.01 samples are composed of mixed anorthic phases?TinO₂n-1,with 8 ? n ? 10?,and the diffraction peaks of Ti10O18 appear in all three of these samples.Tetragonal phase diffraction peaks for the rutile TiO₂ occur in the x = 0.02 sample,but the diffraction peak intensity is low.For the x = 0.04 and 0.08 samples,only the rutile structure can be seen,which suggests that the rutile structure of the samples can be maintained with a higher doping level of Nb up to a temperature of 1473 K.The largest ZT value observed,0.023,was obtained for the x = 0.01 sample at the highest test temperature,380 K.It has been shown that the transport behavior of these samples is consistent with the small polaron conduction mechanism for the temperature range from 300 K to 380 K.2.A series of Nb-doped TiO₂-?(Ti_1-xNb_xO₂-d)ceramics was fabricated using a conventional solid state reaction method with subsequent annealing in an atmosphere of H2.Powder XRD pattern gives the result that x = 0.0,0.01,0.02 and 0.04 samples are composed of mixed triclinic phase TinO₂n-1?4 ? n ? 6?,and tetragonal phase diffraction peaks for the rutile TiO₂ occur in the x = 0.08 and 0.20 samples.For the x = 0.40 and 0.60 samples,only the rutile structure can be seen,which suggests that the rutile structure of the samples can be maintained with a higher doping level of Nb up to a temperature of 1573 K.The thermoelectric properties of these samples were measured in the temperature range from 100 K to 380 K.The largest ZT value observed,0.016,was obtained for the x = 0.20 sample at the highest test temperature,380 K.It has been shown that the transport behavior of these samples is consistent with the small polaron conduction mechanism for the temperature range from room temperature to 380 K.3.PLD technology was used to prepare epitaxial TiO₂ film with a thickness of 119 nm on the?0001?oriented single crystal Al2O3 substrate under a substrate temperature of 550 ?.XRD pattern showed that the as-grown TiO₂ film were?l00?oriented with a structure of rutile and the?200?and?400?crystal plane diffraction peaks appeared at 39.13° and 84.25°,respectively.The Seebeck coefficient and electrical resistivity of the as-grown film were measured using a set of Seebeck coefficient and electrical resistivity test equipment at room temperature.The results were that the electrical resistivity of the film was 130 m?·cm and the Seebeck coefficient was-55 ?V/ K.The power factor was acquired by calculation with a value of 0.0023 mW/?m·K2?.