First-Principles Study on Polymorphs of AgVO3: Assessing to Structural Stabilities and Pressure-Induced Transitions

Abstract

In this paper, we present a comprehensive theoretical study, based on density-functional theory calculations, and which focuses on the structural and electronic properties of silver vanadium oxide (AgVO3) in the monoclinic [Cm (β-AgVO3), C2/c (α-AgVO3), and Cc], orthorhombic (Amm2), and cubic (Pm3̅m) phases from 0–30 GPa. The structural and electronic properties, the stability of different phases, and the pressure-induced solid–solid phase transitions of AgVO3 have been previously studied. The effects of pressure on the band structures, energy–gap values, density of states, and vibrational frequencies are also studied. Numerical and analytical calculations are conducted to obtain the lattice parameters, the bulk modulus K and their pressure derivative K′, and the energy-volume equations of state. The influence of different parametrizations of the exchange-correlation functional (B3LYP, HSE06, and PBE) on the investigated properties is analyzed, and the results are compared to available experimental data. For the first time, a complex and unexpected structural and chemical behavior as a function of pressure is reported. The β-phase is the most stable and the first phase transition between the monoclinic β-AgVO3 and Cc phase takes place at 5 GPa (B3LYP), 3 GPa (HSE06), and 2 GPa (PBE). There are pressure-induced transitions among the β-, α-monoclinic, and cubic structures, and the corresponding values for the pressure transitions are dependent on the functional used. Two new polymorphs, monoclinic Cc and orthorhombic (Amm2), have been characterized for the first time, and their contrasting structural stabilities as well as their transition mechanisms can be understood from the intrinsic characteristics of the crystal lattices. The Badger’s rule is fulfilled for Cm, Amm2, and Pm3̅m polymorphs, while it is invalid for the C2/c and Cc phases. Theoretical results show that the studied reactive channels from β-AgVO3 toward binary oxides, Ag2O and V2O5, AgO and VO2; the elements Ag, V and O2; silver pyrovanadate, Ag4V2O7 and V2O5, as well as Ag2V4O11 and Ag2O are not thermodynamic favorable processes at pressures up to 30 GPa. These results contribute to the understanding of the pressure behavior of AgVO3-based compounds. In addition, it would be interesting to determine whether further measurements and calculations would confirm the predicted structural and thermodynamic properties as well as the solid-state transformations of AgVO3 polymorphs, which have not yet been experimentally shown.