Thermoelectric Properties Of Cu₂S-Based Materials Synthesized By Hydrothermal Method

The excessive use of traditional energy and the growing environmental problems,urge us to develop sustainable,non-polluting new energy materials.Thermoelectric materials can make the heat and electrical energy transform into each other,which have great application prospects in the thermoelectric power generation and thermoelectric cooling technology.As one kind of new high-performance thermoelectric material,Cu_2-x S is a non-toxic and inexpensive raw material,which also is a type of ion conductor owing to the high mobility of Cu+.Cu_2-xS has low thermal conductivity and high thermoelectric figure of merit at high temperature.In this paper,the effects of hydrothermal process parameters on the morphology of Cu₂ S powder were studied.And the influence of the copper vacancy and PbS or SnS content on the thermoelectric properties of Cu₂ S were studied systematically.The main contents of the thesis include the following aspects:1.The Cu₂ S powder was synthesized successfully by hydrothermal method.And the effects of hydrothermal process parameters,such as reaction temperature,the content of surfactants on the morphology of Cu₂ S were studied.Then the Cu₂ S powder was consolidated into bulk by spark plasma sintering?SPS?and its thermoelectric performance was tested.The experimental results showed that the Cu₂ S powder with tetragonal structure and submicron size were synthesized successfully at 160 ? and 180 ?.The average grain size of Cu₂ S power synthesized at 180 ? was smaller than that of 160 ?.Adding proper amount of surfactant sodium dodecyl benzene sulfonate effectively reduced the grain size of Cu₂ S powder and polyhedron morphology appeared in the powder.While proper amount of ethylene glycol was beneficial to form the flake shape Cu₂ S powder.Adding proper amount of surfactants enhanced the thermoelectric properties of Cu₂ S effectively.Electrical conductivity,thermal conductivity and ZT value of different samples had the similar trends with temperature.The maximum ZT value at 873 K was 0.69.2.The Cu_2-x S powder with different Cu+vacancy was synthesized by hydrothermal method and X-ray diffraction was used to analyze the phase and chemical composition of Cu_2-xS powder.Then the Cu_2-x S powder was consolidatedinto bulk by spark plasma sintering and its thermoelectric performance was measured.The experimental results showed that the influence of the copper vacancy on the thermoelectric properties of Cu₂ S was great.The power factor and ZT value of all the Cu_2-xS samples were higher than that of Cu₂ S sample and the thermoelectric properties of Cu1.97 S sample was the best,whose power factor and ZT value at 873 K were 0.95 mW·m-1·K-2 and 1.66,respectively.3.The Cu₂ S powder composite contents of PbS was synthesized by hydrothermal method and then the powder was consolidated into bulk by spark plasma sintering.The effects of PbS content on the thermoelectric performance of Cu₂ S were studied systematically.The experimental results showed that the thermal conductivity of all samples composited with PbS was not reduced,but the electrical conductivity increased significantly.The ZT value increased with increasing temperature.The ZT value of the sample with 0.5% PbS was the highest,which reached 1.88 at 873 K that was about 2.7 times of the pure Cu₂ S sample.4.The Cu₂ S powder composite contents of SnS was synthesized by hydrothermal method and then the powder was consolidated into bulk by spark plasma sintering.The effects of SnS content on the morphology and thermoelectric performance of Cu₂ S were studied systematically.The experimental results showed that the thermal conductivity of all samples composited with SnS had been reduced,however the power factor was also reduced,then the ZT value of samples with SnS were not improved effectively.