Investigation On The Chalcopyrite CuInTe₂ Based Thermoelectric Materials

Thermoelectric (TE) power generation, which can realize the direct conversion between heat energy and electricity, has been considered as one of the sustainable energy technologies to cope with the ever-growing energy crisis and environmental issue, and has great application prospect in industrial exhaust heat recycling. In recent years, a great deal of efforts have been made to improve the TE performance of bulk TE materials used in this temperature range (-800K) and some encouraging results have been achieved, such as a high ZT over 2.0 has been realized in some PbTe-based alloys and compounds used in the middle temperature range. In spite of their high TE performance, however, the hazardous Pb component limits their large-scale application. Therefore, it is necessary to develop other eco-friendly TE materials for middle temperature application. In this scenario, chalcopyrite CuInTe2 has been considered as a promising p-type TE material because of the merits of environmentally friendly chemical component and high stability under operating temperature. Yet, its ZT is unparallel with the well-established n-type TE materials because of the relative high electrical resistivity and thermal conductivity. Thereby, in this work, point defects and nanostructure engineering are employed to regulate the electrical and thermal transport properties of CuInTe2, and a significant enhancement of the TE performance of CuInTe2 has been achieved.1. In the first section, various point defects have been introduced by Cu deficiency, solid solution, cation and anion doping, by this approach, the influence on point defects engineering on the TE performance of CuInTe2 compounds has been elaborately investigated. The main work includes the following four parts:a. Cu deficient bulk Cu1-xInTe2 (x= 0.01,0.02,0.03,0.04) TE materials have been studied, which shown that the electrical conductivity and power factor can be improved effectively due to the introduction of Cu deficiencies, and an enhanced ZT-0.95 at 823 K was obtained in the Cuo0.97InTe2 sample.b. (CuInTe2)1-x(2ZnTe)x (x=0,0.0025,0.005,0.01,0.015,0.02) solid solution samples have been inversitgated, and the results shown the carrier concentration of CulnTe2 was sharply enhanced duo to the formation of ZnIn acceptor point defects, thus the electrical transport properties of CuInTe2 has been optimized and a high ZT-1.2 at 823 K was achieved in the (CuInTe2)o.99(2ZnTe)0.01 sample.c. Cation Q (Q= Mn, Fe, Ni) substitution of In sites was demonstrated in this work, and enhanced electrical properties were gained in the Culno.9sQo.osTe2 (Q= Mn? Fe?Ni) samples, although the thermal conductivity was less affected, an improved ZT-0.98 at 823 K was realized in the CuIn0.95Ni0.05Te2 sample.d. Anion M (M= P, Sb) occupation of Te sites samples CuInTe2-xMx (M=P, Sb; x= 0.01,0.02) were researched, it turned out that the power factor, especially the high temperature power factor of the samples were enhanced due to the improvement of density of states (DOS) by moderate M doping. Therefore, an enhanced ZT-1.1 was reached in the CuInTe1.99Sb0.01 sample.2. Secondly, since the point defects have less impact on the thermal conductivity of CuInTe2 material according to the discussion illustrated above, next, oxidate nanoinclusions were employed to enhance the phonon scattering in the sample to reduce the thermal conductivity of CuInTe2.a. Different topography T1O2 nano powders (nanoparticles (NPs), nanotubes (NTs) and nanofibers (NFs)) were added into the CuInTe2 samples, a displacement reaction has been detected during the hot pressed progress and dispersively distributed In2O3 nanoparticles were formed, rendering a significant reduction of thermal conductivity. By this approach, a large ZT-1.3 at 823 K was obtained in the CuInTe2+0.1 wt% TiO2 NFs sample.b. ZnO nanoparticels were carried out to prepared CuInTe2+x wt% TiO2= 0.5, 1.0,2.0) composites, a displacement reaction has also been observed during the hot pressed progress and produced large amounts of dispersively distributed In2O3 nanoparticles, thus a low thermal conductivity was achieved; In addition, the electrical properties were also enhanced due to the formation of Znjn point defects, overall, a large enhanced ZT-1.44 at 823 K was gained in the CuInTe2+1.0 wt% ZnO sample.3. As aforementioned, the electrical transport properties of CuInTe2 can be optimized significantly by the point defect engineering, and the thermal conductivity of that can be intensively droped by the introduction of nanoinclusinos. Therefore, a simultaneous optimization of both the electrical and thermal properties may be achieved by incorporating both the point defect engineering and nanoinclusions, relative study was list as following.a. The effect of TiO2 nanopowders on the TE performance of the (CuInTe2)0.99(2ZnTe)0.01 solid solution sample was investigated in this work, and a concurrently enhancing in the electrical and thermal transport properties was achieved in the (CuInTe2)0.99(2ZnTe)0.01+T1O2 nanopowders samples. Eventually, an improved ZT-1.47 was obtained in the (CuInTe2)1.99(2ZnTe)0.01+TiO2 NFs sample.b. Nano ZnO powders were enforced into the Anion M (M= P, Sb) doped CuInTe1.99M0.01 (M=P, Sb) samples, by this approach, the electrical transport and thermal transport properties were optimized simultaneously, and an enhanced ZT-1.61 at 823 K was achieved in the CuInTe1.99Sb0.01+1.0 wt% ZnO sample.4. ZnS and ZnSe were also employed to manufacture CuInTe2+x mol.% ZnS (x= 3,6, 12) and CuInTe2+y mol.% ZnSe (y= 3,6,12) composite TE materials; The partial solution of ZnS and ZnSe resulted in a sharp improvement of electrical properties, and the nanoscale ZnS and ZnSe rendered to an intensive reduction of thermal conductivity. Thus a high ZT-1.52 at 823 K was realized in the CuInTe2+6 mol.% ZnS sample.