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

Abstract

Tin dioxide (SnO 2 ) is one of the transparent conductive oxides that has aroused the interest of researchers due to its wide range of applications. SnO 2 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 SnO 2 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, Fm 3̅ m , I 4 1 / amd , and Pnma-II are dynamically unstable. As far as we know, no previous research has investigated the electronic properties of SnO 2 polymorphs from the hybrid functional of Heyd, Scuseria, and Erhzerhof (HSE06) except P 4 2 / 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 SnO 2 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 -SnO 2 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 SnO 2 , rutile is a promising candidate for many applications; however, we investigated the feasibility of the remaining polymorphs for practical applications.

First-Principles Insights into the Relative Stability, Physical Properties, and Chemical Properties of MoSe2

“…Compared to the other stable polymorphs, the 2H-MoSe 2 polymorph shows high vibrational energy, and the free energy is high for the 2H-MoSe 2 polymorph. At extremely low temperatures, entropy stays constant for all polymorphs, and at an absolute zero, it becomes zero . At 1000 K, 2T-MoSe 2 , 3H b -MoSe 2 , and 1H-MoSe 2 polymorphs obtained the constant value 170 J K –1 mol –1 , but 1H-MoSe 2 polymorph showed 140 J K –1 mol –1 of energy as a function of temperature.…”

“…The physical quantities and orientation of Young’s modulus ( E ) and Poisson’s ratio (ν) can be used to show that polymorphs have isotropic characteristics. Young’s modulus ( E ) determines the polymorph’s orientation, which is derived using the given elastic compliance constants . Young’s modulus ( E ) surface should be perfectly spherical for isotropic materials.…”

“…IR spectra are studied for the stable polymorphs, and the corresponding modes of representation are evaluated in this paper . Because of the Se–Mo–Se vibrations, modes of vibrations are prominent in high-frequency regions and some modes are found in low frequencies regions because of Mo–Se vibration (see Table ).…”

“…Table 3 shows the Voigt (V), Reuss (R), and Hill (H) moduli over the elastic stiffness moduli of the stable polymorphs. Additionally, averaging the single-crystal elastic constant leads to finding bulk modulus B and shear modulus G. 46 In Voigt approximation, bulk B and shear G can be defined as…”

Structural, Electronic Properties, and Relative Stability Studies of Low-Energy Indium Oxide Polytypes Using First-Principles Calculations

“…The symmetry of orthorhombic In 2 O 3 polytypes is expressed by the D 2 h ( mmm ) point group and the irreducible representation is Γ = 12 A g + 6 B 1g + 12 B 2g + 6 B 3g + 11 B 1u + 5 B 2u + 11 B 3u ; it consists of four Raman active modes ( A g , B 1g , B 2g , B 3g ) and three IR-active modes ( B 1u , B 2u , B 3u ). 56 Raman spectroscopy of In 2 O 3 - O 1 and In 2 O 3 - O 3 has shown that the frequency spectrum with the strongest peak at 496, and 611 cm –1 , respectively, corresponds to the Raman-active A g mode. The nondegenerate mode A g represents out-of-plane vibrations and they can be symmetric stretch or bend with respect to the principal axis of symmetry of the In 2 O 3 molecule.…”