DFT study of the electronic properties and the cubic to tetragonal phase transition in RbCaF3

Abstract

The structural, elastic, vibrational, and electronic properties of RbCaF 3 in the cubic and low-temperature tetragonal phases have been studied at the ab initio level with density functional theory. Using various exchange-correlation functionals of the generalized gradient approximation for structural properties like the CaF 6 octahedron rotational angle or ratio c/a of the tetragonal lattice constants, it is found that the best agreement with experiment is obtained with the PBEsol and Wu and Cohen (WC) functionals. The fundamental band gap is calculated to be direct and indirect in the tetragonal and cubic phases, respectively. The relation between the cubic and tetragonal phases is studied by monitoring the cubic zone boundary soft mode phonon R 15 as well as the c/a ratio and tilt angle. The results for the Born effective charge tensors are also reported in order to study the effect of the long-range Coulomb interactions. We also investigated the corresponding pressure driven phase transition at T = 0 K, which we observe to be of second order in contrast to the first-order character experimentally detected for the structurally similar high pressure transition at ambient temperature. Based on recently developed finite strain Landau theory, we offer a possible explanation for this peculiar change of character.

Temporal interaction of hybrid signals in various phases of Eu3+: BiPO4 through photon–phonon dressing

“…Temporal interaction with photon-phonon dressing coupling is studied in five types (different molar ratio represents different phases) Eu 3+ : BiPO 4 crystals with C 1 symmetry (less phonon) and D 2 symmetry (more phonon) [9]. To implement the experiments, samples were held in a cryostat (CFM-102).…”

“…Phase transition or lattice symmetry of a functional crystal is one of the important factors in determining its physical properties [5,6]. Present theoretical and experimental studies make available an in-depth understanding of the morphological, structural, electronic, and optical properties of different phases of bismuth phosphate BiPO 4 [7][8][9][10]. The Eu 3+ -doped BiPO 4 crystals with different phases have been reported [10].…”

Red shift of lead-free halide perovskite RbCaCl3 under pressure for enhancing optoelectronic performance

“…A number of compounds with cubic perovskite structure showed promising results in optoelectronic technology [15][16][17]. Especially, calcium (Ca)-based non-toxic alkali halide perovskites ACaX 3 (A = K, Rb, Cs and X = Cl, F) and CsCaBr 3 exhibited promising behavior at ambient pressure [18][19][20][21][22][23][24][25][26][27]. However, some of these compounds may face some limitations to be used in device applications due to their wide band gap nature.…”

Phosphate Ion-Driven BiPO4:Eu Phase Transition

“…Phase transition of functional crystals has been one of the most intensively studied topics in condensed matter physics, chemistry, and materials sciences. − The efficient manipulation of the phase transition usually leads to great improvements in performances of novel materials, and the investigation into this process helps to understand and obtain new crystal structures via rearrangement at atomic scale. The physical nature of the phase transition was illustrated sufficiently well by Guggenheim, Landau, and Lifshitz with an analysis of the behavior of the van der Waals fluid, and as a result of which, the formation of new phase is possible when the corresponding minima of the free energy are less or at least equal to that of the old phase. , Thus, the correct determination of the system free energy in each particular or experimental case is of great importance.…”