Research Projects

Bismuth selenite (Bi2SeO5) crystallizes in the polar Abm2 space group and is structurally related to Bi2TeO5, exhibiting technologically essential properties such as piezo, pyroelectric, and nonlinear optical properties. Compared to Bi2TeO5, studies on Bi2SeO5 in ceramic form are relatively limited. The origin of the polar structural arrangement of Bi2SeO5 is the energy minimization of stereochemically active lone pairs on both Bi3+ and Se4+. Recent reports on Bi2SeO5 as a high-κ gate dielectric for two-dimensional electronics and its unusual mechanical properties, which are suitable for use in flexible devices, underscore the importance of researching this system. The crystal structure of Bi2MO5 (M = Se, Te) can be described as a 2 × 3 × 1 multiplication of the CaF2-type fluorite cell, with nearly 18% of oxygen vacancies. The pseudo-three-dimensional framework of the structure comprises BiO3, BiO6, and MO3 polyhedral units, sharing their edges and corners. In its fully oxidized form, Bi2TeO6 exhibits a cubic fluorite structure. Solid-state chemists play a crucial role in correlating oxygen non-stoichiometry with properties, as this remains an unexplored area in the Bi2SeO5-Bi2SeO6 system. Additionally, with suitable substituents at the Bi-site, one can fine-tune the structure, physical properties, and oxygen mobility in Bi2SeO5. Substituting magnetic trivalent f-block metal ions in place of Bi in Bi2SeO5 and introducing a high entropy effect with these metal ions can, in principle, produce additional effects on its polar structural arrangement, manifesting in interesting physical properties, including a colossal rise in the dielectric constant. Additionally, the magnetic properties of f-block ions under such crystallographically restricted fields have not been well understood. Bi2SeO5 is a wide-bandgap semiconductor (direct bandgap of 3.6 eV); its modification by magnetic rare earths will be reminiscent of a dilute magnetic semiconductor (DMS) scenario. The interplay of three stereochemically active lone pairs of electrons, facilitated by the inclusion of Sb3+ in the structure, will alter the physical properties of Bi2SeO5, leading to a new scenario that has not been explored previously. The substitution of divalent alkaline earth metal ions for Bi3+ in Bi2SeO5 is expected to alter the metal ions' oxidation states, as the charge neutrality principle dictates. The electropositive character of alkaline earth metal ions will also be beneficial in tuning the oxygen stoichiometry and, in turn, their properties. The proposed work will investigate all the above-mentioned aspects to comprehend the structure-property correlations in Bi2SeO5.