Research Projects

Zintl phases are regarded as a class of compounds, which is electronically positioned midway between intermetallics and insulators. A typical Zintl phase, AQx, is the product of formed from the late main group elements Q (viz. Group 13, 14, 15&16) and s-block, that is, alkali metals and alkaline earth metals, A. The Zintl-Klemm concept explains that the valence electrons are transferred from the less electronegative (more electropositive) A, to the more electronegative atom, Q, the latter, thus achieves its closed-shell configuration by forming homonuclear Q-Q bonds. Several polychalcogenide- and poly-pnictide based Zintl phases are known to show nonclassical bonding with bond distances and bond angles that are quite different from those of conventional bonding, such as the oligomeric anionic units. Several such chalcogenides and pnictides (Se, Te) exhibit semiconducting properties. A few of them show significant thermoelectric properties and have been in the limelight of thermoelectric research during the last decade. Zintl phases are generally valence precise, narrow band gap semiconductors and are highly stable. Zintl phases often exhibit high mobility and low thermal conductivity (phonon-glass electron-crystal nature) and form complex structure. These qualities make it ideal as thermoelectric. Therefore, the project covers discovery and fundamental understanding of Zintl-type compounds through exploratory synthesis route and study the complex structural features via single crystal X-ray diffraction method by employing SHELXTL package and Rietveld methods by using GSAS package which would reveal the non-classical bonding interactions. The electronic structure will be studied by DFT calculations (Wien2k package, LMTO47c, BoltzTraP) and evaluation of physical properties such as electrical and thermal conductivity, thermoelectric power by using advanced measurement techniques available at CSIR-NIIST. This project is as a part of our bigger initiative on development of thermoelectric materials.

0