Executive Summary : | The proposed work focuses on new multifunctional perovskites of transition metal halides for enhanced magnetic, optical and ferroic properties. A multifunctional material is the one which shows two (or possibly more) functional properties simultaneously and holistically. Ever since the 2009 discovery of photovoltaic application of (MA)Pb(I/Br)₃ (Kojima, 2009), halide perovskites have become widely studied optoelectronic materials. In the past few years, other exciting properties including piezoelectric, pyroelectric, and thermoelectric have been found in these materials. In parallel, halides of divalent 3d metals (such as Cr, Mn, Fe, Cu) have been studied due to their intriguing crystal field splitting, orbital ordering, and magnetic exchange. Often, optical, ferroic and magnetic properties are found independently. Finding them simultaneously and holistically can provide several new opportunities and are expected to show wide technological applications including in memory devices, energy storage and conversion devices, and switching devices. If magnetic, electric, and ferroelectric properties are to be found simultaneously in the same or in the related materials, they demand that the material should have extended structure with unpaired spin, and possibility of ordered-disordered or centrosymmetric to non-centrosymmetric phase transition. The former condition is required for magnetic; the latter condition is required for ferroic properties. The proposed work aims to develop new bimetallic transition metal halide perovskites with major objectives as given below: (i) To develop materials with magnetic metal ion in 3-D framework, 2-D sheet, and 1-D chain. The 3-D systems are expected to contain tetrahedrally clustered magnetic ions and are designed as models for frustrated lattices where no ordered state can simultaneously satisfy all nearest-neighbour magnetic exchange. Such systems have potential to be used in quantum computing. The comparison of exchange interactions between 3-D, 2-D, and 1-D materials will provide insight into magnetic exchange phenomenon. Furthermore, the materials of different dimensionalities will be utilized as models for understanding electronic structures in different dimensionalities. (ii) To develop bimetallic layered halides, (NH₃-R’-NH₃)₂M(II)M(II)Cl₈ as redox-switchable materials in which at least one of the metals (Cr, Mn, Cu) can show distorted to undistorted [(Cu(II) + M(II) ⇌ Cu(I) + M(III)] phase transition through Jahn-Teller distortion at relatively mild conditions (or hopefully under normal conditions). In-plane Jahn-Teller distorted phase is expected to show better electric polarization due to likelihood of high dielectric constants. (iii) To develop chiral halide perovskite crystals by incorporating chiral amines as the cation in the interlayer spaces. This will enable us to examine properties of chiral ferroelectrics when the materials are non-centrosymmetric with antiferrodistortive perovskite framework. |