Investigation On The Preparation And Properties Of ZnO Based Thermoelectric Materials

Thermoelectric(TE)materials are a kind of semiconductor functional materials,which can be used to convert heat energy directly into electricity or reversely.They are of interest for applications in TE cooling devices and power generators.Recently,ZnO-based compounds becomes an outstandingly promising oxide materials as a high-temperature thermoelectric material because of its high melting temperature,good chemical stability,high electrical conductivity,and high Seebeck coefficient.ZnO-based thermoelectric materials were selected as our research object.In the experiments,ZnO-based compounds powder were fabricated by sol-gel method,Then ZnO-based compounds block were fabricated by hot-pressed sintering.The microstructures of the samples were characterized by XRD,SEM et al.The thermoelectric properties were determined by measuring electrical conductivity, Seebeck coefficient and power factor.The effect of processing parameters to thermoelectric propeties were analyzed by uniform experiment and orthogonal experiment.Results show that the appropriate processing parameters are:sintering at 920℃,forming pressure at 2.7MPa and holding time within 40 min.TEM was used to characterize the microstructure of the samples.It is revealed that the samples are low in density,and have many pores to be effective to decrease the thermal conductivity.In order to improve the TE properties of samples,Al,In,Ce,Y and Al-Ce doped were tried.Results indicate that,except Y-doped,the dopants affect the thermoelectric properties of the samples greatly and they can improve the thermoelectric properties in different extent.It also exists an appropriate range of doping values to improve the thermoelectric properties of the samples.Electrical conductivity and Seebeck coefficient of the samples are measured at temperatures ranging from 500℃to 900℃. Electrical conductivity of samples increase with increasing temperature and the dopants content.Seebeck coefficient of the samples show negative and the absolute value increase approximately with increasing temperature and decrease with increasing the dopants content.The highest values of electrical conductivity were observed for Al-Ce doped in the range of 11.5 to 40.0Ω^-1cm^-1,the lowest ones for Y-doped in range of 4.2 to 16.4Ω^-1cm^-1.The highest absolute values of Seebeck coefficient were observed for In-doped in range of-164 to -397μVK^-1,the lowest ones for Al-Ce doped in range of-68 to -156μVK^-1.In the all samples,The highest value of power factor(3.1×10^-4Wm^-1K^-2)was attained for 2mol%In-doped sample at 900℃.