Research

Research Interests:

Our group's research focus is on “Defect Engineering of Multifunctional Materials”. It focuses on controlling the growth and properties of a wide range of thin films, nanostructures, complex heterostructures, and 2D materials, characterizing the structural and compositional properties by a wide range of techniques with a special focus on high-resolution transmission electron microscopy (HRTEM) and spectroscopic techniques (XPS, Raman, UV-vis, IR) to understand the defect-structure property correlations of multifunctional materials. Semiconducting oxides, multiferroics, nanostructured magnetic materials for sensor applications, transition metal chalcogenides, and nanostructured oxides for energy conversion applications are the areas of focus in our research group. Currently, three major topics of research viz, (i) Magnetic and multiferroic materials, (ii) Materials for semiconductor, perovskite, and quantum dot sensitized solar cells, and (iii) Developing cathode and anode materials for Li-ion battery applications are being pursued rigorously in the group. Topical research interests and highlights are briefly given below.

Microscopic (TEM & HRTEM) and spectroscopic investigations of defects: Role of defects (surfaces, interfaces, and defects) on the physical (optical, electrical, and magnetic) properties of multifunctional oxides, sulfides, and nitrides are correlated to the defect structure studies made using HRTEM imaging. We have studied in detail the defect-structure properties of aliovalent doped BiFeO₃ nanoparticles, MoS₂ nanosheets, oxides like ZnO and TiO₂, Chalcogenides, etc. The materials and their properties specifically focused on are given below.

Defect controlled structure-property correlations in multifunctional oxides and multiferroics:

Oxygen vacancy defects significantly influence the properties of oxides, specifically in nanoparticulate systems. We have demonstrated that the defect states due to oxygen and microstrain are strongly influenced by the BiFeO₃ particle size and significantly affect the shape of absorbance curves. Microstrain in the lattice leads to the reduction in rhombohedral distortion of BiFeO₃ for particle sizes below 30 nm. The decrease in bandgap with decreasing particle size is attributed to the competing effects of microstrain, oxygen defects, and Coulombic interactions. Further, the structural changes due to the oxygen vacancy alter the magnetic interactions, which bring in weak ferromagnetism in BiFeO₃. We additionally controlled oxygen vacancy concentration by carrying out controlled doping experiments. With this, magnetic, magnetodielectric, and photovoltaic properties are tuned. Thus, bismuth ferrite-based materials are shown to be potential for all-solid-state photovoltaic and magnetic-sensor device applications. We demonstrated the best photovoltaic device efficiencies of 0.22% and the magnetodielectric response of 10% by establishing the right balance between the oxygen vacancies concentration and the ferroelectric properties.

Nanostructured oxide materials for Li-ion battery (LIB): Synthesizing cathode and anode materials for LIB in the form of nanowires and nanotubes; Studying the effect of particle size, microstructure, dopants, and defects on the electrochemical characteristics to understand the basis of the materials for optimizing cathode and anode performance for Li-ion battery application is the focus of research on energy storage materials. Li-ion batteries are very promising for many applications, including portable electronic devices and electric vehicles. The study in our group aims to understand the limitations due to poor ionic and electronic conductivity. And further improve the capacity, rate capability, cyclic stability of LIB. Materials of current interest include nanostructured LiFePO₄, Li₄Ti₅O₁₂, LiVPO₄, Li₂FeP₂O₇, Li-rich layered compounds, and solid electrolytes. More specifically, we address the role of microstructure, composition, and defects on the electrochemical properties of cathode and anodes.

Nano-oxides, semiconductor thin films, quantum dots for and perovskite for solar cell applications: Synthesis and fabrication of nanostructured oxides (TiO₂, ZnO, SnO₂) in the porous form, tuning material interface for efficient electron injection and transport, bandgap engineering of nano-oxide and composite materials for increasing efficiency of dye and quantum-dot sensitized solar cell; Synthesis and characterization of thin films and quantum dots of semiconductor and perovskites (organic and inorganic). We recently developed a modified dye/QD sensitized solar cell configuration in which whispering gallery mode resonating cavities are used in the photoanode. This significantly enhances the efficiency of the solar cells. These solar cells, named "Whisperonic solar cells," are very promising for enhancing efficiency. Various fundamental studies, including the understanding of the light-matter interaction, are being explored. Kesterite and perovskite solar cells both in thin-film and quantum dot configurations are being studied.

In-situ electrical and optical probes under high-vacuum and controlled atmosphere annealing to study oxygen vacancy influenced changes in the properties of oxide thin films

It is important to understand how the inclusion of defects qualitatively changes the electrical transport properties, which in turn are influenced by the simultaneous changes in the structural and chemical modifications. The changes that take place during the inclusion of defects can be monitored by carrying out the in-situ measurements on electrical and optical response and structural changes. We developed equipment to carry out measurements in situ on the electrical properties of the material under vacuum and controlled gas atmosphere of wide bandgap oxide thin films. The equipment will be upgraded to study the in situ optical (photoluminescence and Raman) and chemical (x-ray photoelectron spectroscopy) changes that take place under vacuum and controlled atmosphere treatment.