Zintl phases attract much attention from a fundamental stand point because of the appeal of their diverse crystal and electronic structures. Recently, reports on unusual magnetic, electronic and thermoelectric properties within the realm of some ternary Zintl phases have generated renewed interest in these materials from a practical position, and have opened new research opportunities for solid-state chemists. Yb14MnSb11 has generated significant interest not only due to its high efficiency as a thermoelectric material but also because of its unique low temperature magnetic and electronic properties. The ef?ciency of a thermoelectric TE material performance is quanti?ed by a dimensionless ?gure of merit ZT=S2 oT/e, where S is the Seebeck coef?cient, o is the electrical conductivity, e is the thermal conductivity, and T is the absolute temperature.Accordingly, A good TE material with high ZT value requires the combination of high electrical conductivity, low thermal conductivity, and high thermopower or Seebeck coef?cient S. Materials that meet these requirements are found for typically heavily doped, small band-gap semiconductors or semimetals. The application of TE materials, in detail Yb14MnSb11, depend on the behavior at high temperatures. All the physical measurements have showed that Yb14MnSb11 does not decompose or change phase within the temperature range needed for deep space power generation. However, in recent years it has been found that average rates of the Yb14MnSb11 sublimation measured at 1000°C in vacuum are unacceptably high to provide long term use of the material for this action. An expected strategy to improve efficiency force applications of Yb14MnSb11 is to consider mixed cations in the Yb14-xLnxMnSb11 compounds. Doping of Yb14MnSb11 by Ln3+ might be a way of improved thermal stability due to the replacing Yb2+ by Ln3+ with the vapor pressures at 1000°C being ten orders of magnitude lower than this of Yb, and the La, Gd and Lu elements show the least vapor pressure. The change should reduce total vapor pressure under the alloyed solids and their sublimation rate. In recent years the solid solutions with Ln3+ = La, Ce, Gd, Tb-Ho, Tm and Lu have received substantial attention with an emphasis on optimization of thermoelectric properties through tuning of the carrier concentration of the matrix. Alloying by Ln improved these properties of Yb14MnSb11. However, only small amounts of Ln3+ can be incorporated in Yb14-xLnxSb11 (x ? 0.7). In order to increase the amount of Ln, an equal amount of germanium (Ge) and silicon (Si) can be substituted for Sb to form Yb14-xLnxMnSb11-yGey or Yb14-xLnxMnSb11-ySiy in order to increase the bandgap and melting point. Additionally, the series of compounds Yb14-xLnxMnBi11 are of interest. Yb14MnBi11 is a smaller bandgap with higher conductivity than Yb14MnSb11 and may result in unusual magnetic coupling or other properties. Therefore, synthesis, crystals growth, characterization of new thermoelectrically materials is an important endeavor.
The main of the project will be synthesis, growing single crystals substance, investigated new Zintl phase based on pnictides of rare earth and transition metals, the study of their thermodynamically and physical properties as well as applications as high-temperature thermoelectric materials for energy generation from waste heat sources.
New materials were found by building new phase diagrams, emphasizing new Zintl phases, investigating their thermal, magnetic, electrical properties to develop new technique, particularly to transfer energy to long distances.
Status in the sphere of investigations in the Institute of Chemistry AS RT:
1. All phase diagrams of Ln-Sb, Ln-Bi 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-o LnxMnSb11 , where Ln- Gd,Dy,Tb, Er,Ho,Tm, Lu and Yb14MnSb11-xTex, have been obtained and investigated.
Effect 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.
