Cu_2-xSe Prepared By The Hydrothermal Method And Its Dispersion Effects On The Thermoelectric Properties Of Some Oxide Materials

In recent years,the development of new energy sources and energy conversion technologies have become a hot topic of scientific research with the drastic reduction of fossil fuels and the deterioration of environmental pollution problems.Thermoelectric materials can achieve a direct conversion between heat energy and electric energy,it is a promising new energy material,which applys to the fields of thermoelectric power and thermoelectric refrigeration.The performance of the thermoelectric materials is highly governed by the dimensionless figure of merit ZT values.Currently,there are many ways to improve thermoelectric performance,energy band engineering and nanostructure are two important methods.In 2011,after the concept of"electronic crystal-phonon liquid"was proposed,researchers discovered the new thermoelectric materials Cu_2-xSe.In this paper,Cu_2-xSe nanopowders were fabricated using the hydrothermal synthesis,and then hot-pressed into bulk alloys,the thermoelectric performance of Cu2-xSe bulk alloys was investigated.It was found that the pure Cu2-x Se nanopowders were prepared by adding the right amount of hydrazine hydrate,the crystal particles of Cu_2-xSe also homogenized gradually with the increase of hydrazine hydrate.Then the pure Cu2-xSe anopowders were pressed into bulks by vacuum hot pressing,Cu2-xSe experienced secondary growth form cubic phase to orthorhombic phase in the process of hot pressing,there were many thin lamellar structures in the cross-section of Cu2-xSe.The parameters of thermoelectric performance of Cu2-xSe bulk alloys were affected by hot-pressing temperature.Finally the ZT value of 973 K hot-pressing Cu_2-xSe bulk alloys sample reached 0.92 at 873 K.In addition,it was found that selenium was easy to volatilize in high temperature.The oxide thermoelectric materials have the properties of high chemical and thermal stability.According to the literature,elemental doping and material composition can improve the thermoelectric properties of materials effectively.Bi₂Ba₂Co₂O_y,Bi₂Sr₂Co₂O_y are all the cobalt oxide with good thermoelectric properties.Cu_2-xSe,Bi₂Ba₂Co₂O_y,Bi₂Sr₂Co₂O_y are also the p-type thermoelectric material.In this paper,the Cu2-xSe nanopowders prepared by hydrothermal synthesis dispersed in the microstructure of Bi₂Sr₂Co₂O_y,Bi₂Ba₂Co₂O_y and Na element doped Bi_1.8Na_0.2Sr₂Co₂O_y,Bi_1.975 Na_0.025 Ba₂Co₂O_y according to a certain mass ratio.The dispersion of Cu2-xSe did not change the lattice parameters of these oxide materials,but changed the morphology of their cross sections.In addition,the dispersion effect of Cu_2-xSe could reduce the resistivity and thermal conductivity,thus increased the ZT values of oxide thermoelectric materials.Among the samples,the ZT value of Bi₂Sr₂Co₂O_y+0.50 wt%Cu_2-xSe sample increased by 26%compare with the Bi₂Sr₂Co₂O_y sample at 873 K,the ZT value of Bi₂Ba₂Co₂O_y+0.50 wt%Cu_2-xSe sample increased by 35%compare with the Bi₂Ba₂Co₂O_y sample at 873 K,the power factor of Bi_1.8 Na_0.2.2 Sr₂Co₂O_y+0.25 wt%Cu_2-xSe sample increased by 18%compare with the Bi₂Sr₂Co₂O_y sample at 923 K,the power factor of Bi_1.975 Na_0.025 Ba₂Co₂O_y+0.25wt%Cu_2-xSe sample increased by 31%compare with the Bi₂Ba₂Co₂O_y sample at 898 K.