Research On N-type Bi₂Te_2.7Se_0.3 Thermoelectric Materials By Compositing And Doping

Thermoelectric materials are considered to be a sort of semiconductors which couldrealize energy conversion between heat and electric energy directly. The devices made bythermoelectric materials have as advantages of no-moving part, noiselessness, lowmaintenance and environmental protection. It has extremely significant application for thehigh-performance thermoelectric materials to alleviate crisis of energy and environmentpollution. The thermoelectric performance depends on the dimensionless figure meritZT=S~2σ/κ, where T，S，σ，κ is absolute temperature, Seebeck coefficient, electricconductivity and thermal conductivity, respectively. The larger ZT arrives, the betterthermoelectric performance and higher conversion efficiency will reach. So far, Bi2Te3hasthe best thermoelectric performance and wide commercial application around roomtemperature. The n-type Bi2Te2.7Se0.3alloys are proved to have better thermoelectricperformance according to the latest papers. In this dissertation, the Bi2Te2.7Se0.3alloys werefurther studied for higher ZT.Firstly, nano powders of AZO (Al0.03Zn0.97O) and TiN are composited in n-typeBi2Te2.7Se0.3alloys. We expect the boundaries between external nano particles and of thematrix would cause stronger scattering ofthe phonon to decrease the lattice thermalconductivity. In addition, the boundary barrier due to the difference of energy band from twotypes of materials could lead the energy filtering effect which is preferable to enhance thepower factor and get better ZT value.Secondly, Al and Fe, were doped in Bi2Te2.7Se0.3alloys, with the aim of adjusting theconcentration of carrier to optimize the power factor for better thermoelectric performance.The results showed that both of the composting and doping could improve thethermoelectric performance resulting from the increased power factor and decreased thermalconductivity below the400K. If the temperature is beyond that temperature, the resultsbecome worse. What’s more, conduction type of matrix materials is changed when excessiveTiN is added into the Bi2Te2.7Se0.3alloys. We connect this phenomenon with the defectswhich are brought by the external particles, and further investigations are needed to study thedetails.The particular mechanism of carrier production gives rise to significant fluctuation ofcarrier concentration which leads to the poor reproduction of n-type Bi2Te3. At last, thisdissertation improves the reproducibility to some extent by accurately control of thefabrication method.