Preparation And Properties Of Cu₃SbSe₄ Based Thermoelectric Composites

Developing the eco-friendly and renewable energy is regarded as one of the important and effective means to solve the current energy crisis.In recent years,thermoelectric（TE）technology provides a clean and efficient energy solution in waste heat recovery and solid-state refrigeration,which has a bright application prospect.As a typical ternary Cu-based compound,Cu₃SbSe₄is considered as a promising medium temperature thermoelectric material due to its adjustable electrical properties and low thermal conductivity.Nano-compositing is an effective approach to enhance the thermoelectric properties of materials.Nanostructuring could provide an effective phonon scattering and decrease the thermal conductivity without seriously sacrificing the electrical conductivity.In this study,the second phases were introduced into the Cu₃SbSe₄ matrix and the composites were prepared by ball milling（BM）and rapidly hot-pressing（RHP）sintering.Microstructure and thermoelectric transport properties of composites were analyzed.The effects of graphene,tin telluride and nano oxide on the properties of Cu₃SbSe₄ were studied.The main results were listed as follows:1.In order to optimize the electrical properties of Cu₃SbSe₄,graphene nanosheets were introduced into Cu₃SbSe₄ matrix.Microstructure and thermoelectric transport properties of graphene/Cu₃SbSe₄ composites were analyzed.It was found that the the addition of graphene effectively decreased the grain size of Cu₃SbSe₄.With the content of graphene increasing,the electrical conductivity of graphene/Cu₃SbSe₄ composites increased greatly due to the increase of hole carrier concentration resulting from the introduction of graphene.Moreover,the incorporation of graphene decreased the lattice thermal conductivity effectively.The maximum ZT of 0.67 for 2.00%graphene/Cu₃SbSe₄ composite was achieved at 650 K,which was 3.19 times higher than that of pure Cu₃SbSe₄.2.In order to further tune the carrier concentration of Cu₃SbSe₄ and optimize the electrical properties of Cu₃SbSe₄,nano-Sn Te was introduced into Cu₃SbSe₄ matrix.The phase composition,microstructure and thermoelectric transport properties of Sn Te/Cu₃SbSe₄composites were characterized.The results showed that the cooperation of nano-Sn Te tuned the carrier concentration and improved the electrical conductivity greatly,which correspondingly enhanced the power factor of pure Cu₃SbSe₄.Moreover,the existence of nano-Sn Te particles and nanopores enhanced the scatter of high-frequency phonons and decreased the thermal conductivity of Sn Te/Cu₃SbSe₄ composites obviously.The maximum ZT of 0.71 for the 2.00%Sn Te/Cu₃SbSe₄ composite was obtained at 650 K,which was 3.4times higher than that of pure Cu₃SbSe₄.3.In order to suppress the deterioration of Seebeck coefficient and reduce the thermal conductivity of Cu3SbSe4,the effect of nano zirconia on the thermoelectric transport properties of Cu3SbSe4 was studied.Nano-ZrO₂ particles were dispersed at the grain boundary of Cu3SbSe4 matrix,which effectively inhibits the growth of composite grains during rapidly hot pressing sintering.The minimum average grain size of ZrO₂/Cu3SbSe4composite samples was less than 1μm.The deterioration of Seebeck for composites was restrained to a certain extent.Nanopores,nano-ZrO₂ particles and reduced grain size made a great contribution to scattering more phonons and reducing thermal conductivity.At 650 K,the maximum ZT value of 1.00%ZrO₂/Cu3SbSe4 composite was 0.57,which was three times higher than that of pure phase.4.In order to find suitable nano oxide additives,the effects of nano titanium oxide,nano tungsten oxide and nano lanthanum oxide on the thermoelectric transport properties of Cu3SbSe4 were studied.The results showed that the electrical conductivity of La₂O₃/Cu3SbSe4composite increased most obviously.Nano-TiO₂ and nano-WO₃ played a positive role in inhibiting the decline of Seebeck coefficient of Cu3SbSe4.Due to the existence of nano phase and the decrease of the average grain size,the thermal conductivity of composites decreases obviously.At 650 K,excellent results of ZT_max=0.53,ZT_max=0.85 and ZT_max=0.76 were achieved in 0.50%TiO₂/Cu3SbSe4,0.50%WO₃/Cu3SbSe4 and 0.50%La₂O₃/Cu3SbSe4thermoelectric composites,respectively.The effect of nano WO₃ was the most obvious,which was 4.25 times higher than that of Cu₃SbSe₄ matrix.