First-Principles Exploration into the Physical and Chemical Properties of Certain Newly Identified SnO₂ Polymorphs

Tin dioxide (SnO₂) is one of the transparent conductive oxides that has aroused the interest of researchers due to its wide range of applications. SnO₂ exists in a variety of polymorphs with different atomic structures and Sn-O connectivity. However, there are no comprehensive studies on the physical and chemical properties of SnO₂ polymorphs. For the first time, we investigated the structural stability and ground-state properties of 20 polymorphs in the sequence of experimental structures determined by density functional theory. We used a systematic analytical method to determine the viability of polymorphs for practical applications. Among the structurally stable polymorphs, Fm3̅m, I4₁/amd, and Pnma-II are dynamically unstable. As far as we know, no previous research has investigated the electronic properties of SnO₂ polymorphs from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06) except P4₂/mnm, with calculated band gap values ranging from 2.15 to 3.35 eV. The dielectric properties of the polymorphs have been reported, suggesting that SnO₂ polymorphs are also suitable for energy storage applications. The bonding nature of the global minimum rutile structure is analyzed from charge density, charge transfer, and electron localization function. The Imma-SnO₂ polymorph is mechanically unstable, while the remaining polymorphs met all stability criteria. Further, we calculated Raman and IR spectra, elastic moduli, anisotropic factors, and the direction-dependent elastic moduli of stable polymorphs. Although there are many polymorphic forms of SnO₂, rutile is a promising candidate for many applications; however, we investigated the feasibility of the remaining polymorphs for practical applications.