With increase in the world’s population, competition for energy is acute and development of new materials for energy conversion has became a topic of research. One of new class materials for utilization as high-temperature thermoelectric materials with Zintl bonding (Zintl phases). In 2006 Yb14MnSb11 was reported to be a good p-type thermoelectric material with a figure of merit (zT) around 1 at 1223K, creating a new field of study for this structure in particular as well as Zintl phases in general. Efficiency of these materials for conversion of thermal energy into electrical depends on the dimensionless figure of merit zT, where zT = S2T/rk, , and S = Seebeck coefficient, r = electrical resistivity, and k = thermal conductivity. YbCd1.6Zn0.4Sb2 which has a zT of 1.2 at ~700K and Yb1-xRExZn2Sb2 or other 1-2-2’s show promise for high zT. The addition of a 3+ rare earth element to donate electrons to the system will allow for tuning of the electronic states with the goal of increasing zT to above 2. Seebeck coefficient can be increased by the pressure including chemical in order to obtain the maximum value zT. The replacement of a 2+ rare earth with a 3+ rare earth has a similar effect as pressure in order to further optimize the properties. So when ytterbium is partially replaced by lanthanum, the zT coefficient will increase. There is great interest in developing new compounds and characterizing these new Zintl phases.
High-temperature thermoelectric materials are becoming increasingly useful for applications such as power generation of deep space probes, sea buoys and remote telecommunications. Thermoelectric devices are considered environmentally- benign - power sources that could provide part of the solution to today’s energy problem. Thermoelectric generators convert thermal energy directly into electrical energy, require little to no fuel, minimal maintenance and can be designed to operate over a large temperature range (300-1275K). Yb14MnSb11 has been segmented with skutterudites by the Jet Propulsion Laboratory to improve the efficiency of radioisotope thermoelectric generators (RTGs). Combinations of di?erent elements lead to variations in structure and properties due to changes in electronegativity, valence and ionic radii. Systematic synthesis and crystal growth is important for the characterization of new thermoelectrical materials. The main of the project will be synthesis, growing single crystals substance, investigated new energy efficiency Zintl phase based on pnictides , the study of their thermochemistry, physical properties as well as applications as high-temperature thermoelectric materials for energy generation from waste heat sources and as energy efficiency materials.
Status of investigations in the Institute of Chemistry AS RT:
1. All phase diagrams of Ln-Sb, Ln-Bi systems systems, have been studied.2. Eu-Mn-Sb, Eu-Mn-Bi, Yb-Mn-Sb, Yb-Mn-Bi subsystems have been studied and the number of new, triple non-organic compounds which can be considered the new Zintl phase, have been obtained.3. Monocrystals Yb14MnSb11 and its solid solutions with composition Yb14-х LnxMnSb11 , where Ln-La,Pr,Nd,Sm, Gd,Dy,Tb, Er,Ho,Tm, Lu and Yb14MnSb11-xTex, have been obtained and investigated.
Impact of suggested project on the progress in this sphere.
As we know, issue of thermal energy transformation into electrical, its transmission to the long distances is one of the most important goals of science and engineering. As a result of synthesis of new materials that promote to solve this issue, makes its contributions to the progress of this sphere. This type of transformation of thermal energy into electrical is ecologically clean method. Besides, the obtained material will be of scientific value expanding knowledge of interesting class of non-organic compounds formed by electropositive elements and elements with Zintl bonding.
Expected results and their application.
In the result of the works new materials with high zT will be obtained to transform thermal energy into electrical and to transmit them to long distances energy generation from waste heat sources, as energy efficiency materials. Building of new triple phase diagrams, doping of Yb-Sb-Cd, Eu-Sb-Mn, Yb-Sb-Zn will contribute to the development of technological process of these materials considering minimal negative effect made on humans, animals and environment.
