Complex oxides and chalcogenides show a wide range of interesting and useful properties such as superconductivity, ferroelectricity, thermoelectricity, magnetism etc. The focus of this research area will be to identify or design new materials and tailor the physical properties of such oxides and chalcogenides using both modern and conventional principles of materials science. Typically, such approaches include hetero-structuring of structurally dissimilar materials, chemical doping etc.
We are interested in develop chemical design principles for complex ternary and quarternary materials, to achieve multifunctional properties, which are often not seen in a single material. The rich chemical flexibility of ternary and quarternary systems allows us to pick and choose the right chemical components to achieve such conflicting physical properties. One possible example is the family of materials known as perovskite chalcogenides. These materials possess a chalcogen (sulfur, selenium or tellurium) instead of oxygen in the well known oxide perovskites. We have successfully synthesized several varients of these materials and have shown that they can be a good material for a variety of optoelectronic applications. (See figure below)This thrust will bridge the knowledge gap for such classes of functional materials with equal focus on synthesis of materials, characterization, measurement of properties and making devices from such materials.
The optical image of powder and pellets of perovskite chalcogenides shown along with the schematics of their crystal structure, and the optical properties as characterized by photoluminescence spectroscopy. (S. Niu et al. Advanced Materials (2017))
S. Niu, H. Huyan, Y. Liu, M. Yeung, K. Ye, L. Blankemeier, T. Orvis, D. Sarkar, D. J. Singh, R. Kapadia, and J. Ravichandran, “Band-Gap Control via Structural and Chemical Tuning of Transition Metal Perovskite Chalcogenides", Advanced Materials, 29 1604733 (2017).
J. Ravichandran, W. Siemons, D-W. Oh, J. T. Kardel, A. Chari, H. Heijmerikx, M. L. Scullin, A. Majumdar, R. Ramesh and D. G. Cahill, “High temperature thermoelectric response of double-doped SrTiO3 epitaxial films”, Physical Review B, 82, 165126 (2010).
J. Ravichandran, W. Siemons, H. Heijmerikx, M. Huijben, A. Majumdar and R. Ramesh, “An epitaxial transparent conducting perovskite oxide: double-doped SrTiO3”, Chemistry of Materials, 22, 3983 (2010).
W. Gao, A. I. Khan, X. Marti, C. Nelson, C. Serrao, J. Ravichandran, R. Ramesh and S. Salahuddin, "Room temperature negative capacitance in a ferroelectric-dielectric superlattice heterostructure", Nano Letters, 14, 5814-5819 (2014).