Research Projects

The main objective of this proposal is to use solid state chemical synthetic route to explore lithium and sodium containing metal borate halide as inorganic solid-state conductors with multi-anionic frameworks. This proposal aims to use lithium/sodium hydroxide and halides eutectic mixtures as fluxes to act as a reactive medium for discovery and to grow single crystals that will be used for complete structural characterization using X-ray diffraction technique. Another important aspect and the scientific rationale of using these active fluxes is that they are known to actively participate in the reaction leading to dimensional reduction of the frameworks and incorporation of halide anion as a second ion into the crystal structure. Potassium, Cesium, and Rubidium metal borates e.g. K₂Al₂B₂O₇, RbTaB₂O₆, CsNbB₂O₆ have been widely studied in the applications of Non Linear Optics (NLO) due to their high band gap and relatively high air stability. The same fundamental properties would make their lithium and sodium analogues suitable candidates as ionic conductors which have hardly been studied in the literature. Furthermore, formation of crystallographically ordered multi-anionic compound have two major advantages: first, these compounds are stabilized by a high configurational entropy compared to a single anion containing compound. This phenomenon is similar to the stabilization of high entropy alloys. thereby can solve the poor stability issues faced by the traditional oxide, chalcogenide and halide based solid state conductors. Second, presence of multiple anions can influence the local coordination environment of the fast ions (Li+ and Na+) due difference in electronegativity of the anions, which ultimately can modulate the ionic conductivity of the material. In this proposal, the multi-anion approach will be used on a wide variety of three dimensional metal borates (e.g. AMB₂O₆, A₂M2B₂O₇, A₃M₂[BO₃]₃, AM₄[BO₃]₃; where A is Li and Na; M is main group and p-block metals such as Ca, Ba, Sr, Sb, In, Sn, Ge, etc.) to demonstrate structural diversity resulting from the inclusion of halide ions (F-, Cl-, Br- and I-) using detailed X-ray diffraction on single crystals and powder samples, nature of bonding using FTIR, Raman and X-ray photoelectron spectroscopy, and ultimately to test the conductivity of the compounds and electrochemical stability using an impedance analyzer with a potentiostat and understand how the structure of these materials affects their properties. Alongside the solid state technique used for the synthesis of the metal borate halide, a second alternate approach involving hydrothermal growth using aqueous mixtures of the precursors and boric acid as a source of borates group will be used to mitigate the risk. This project will pave the way to the design and development of new solid ionic conductors with high ionic conductivity comparable to liquid electrolytes that can be used to build All Solid State Batteries (ASSBs).