Structural, vibrational and electronic properties of SnMBO₄ (M  =  Al, Ga): a predictive hybrid DFT study

Abstract

We propose two new members of the mullite-type family, SnAlBO 4 and SnGaBO 4 , and carry out an in-depth study of their crystal properties using the hybrid method PW1PW. Both are isostructural to PbMBO 4 (M = Fe, Mn, Al, Ga), which show axial negative linear compressibility (ANLC), among other interesting features. We find that, although Sn 2+ is susceptible of being oxidized by oxygen, a suitable range of experimental parameters exists in which the compounds could be synthesized. We observe absence of ANLC below 20 GPa and explain it by the small space occupied by the lone electron pairs, as indicated by the small length of the corresponding Liebau Density Vectors. In agreement with this fact, the structures present a low number of negative mode-Grüneisen parameters, which may also suggest lack of negative thermal expansion. The electronic properties show a remarkable anisotropic behaviour, with a strong dependence of the absorption spectra on light polarization direction.

Effect of R-site element on crystalline phase and thermal stability of Fe substituted Mn mullite-type oxides: R2(Mn1−xFex)4O10−δ (R = Y, Sm or Bi; x = 0, 0.5, 1)

“…Examining the stereochemical activity of Bi lone electron pair also lead to the same conclusion. 42 In contrast, experimentally we observed the reverse, 1227 K for Bi 2 Fe 4 O 9 vs. 1217 K for Bi 2 Mn 4 O 10 . The reason is that the decomposition products of Bi 2 Fe 4 O 9 are also less stable than those for Bi 2 Mn 4 O 10 , with 0.8 eV per formula unit higher energy.…”

Importance of Surfaces and Many-Body Absorption Spectra for C-Doped TiO2 Photocatalysts

“…Therefore, for selected systems, geometry optimizations were also performed at this level using the CRYSTAL17 code. We employed the hybrid method PW1PW, which includes 20% of Hartree–Fock (HF) exchange and has been shown to appropriately describe a broad range of crystalline compounds , as well as TiO 2 surfaces. , We note that a self-consistent method to determine the optimal fraction of HF exchange based on the dielectric constant has been recently implemented in CRYSTAL . By applying it to anatase, we found that this value is 18%, that is, very close to that used by the PW1PW functional.…”

Characterization of Multiferroic Bi2Mn4O10 by Dielectric and Neutron Spectroscopy

“…Hence, direct electron hopping is more likely in the b ‐direction where the distance between manganese ions is shorter by about 20 pm, and the overlap of 3d‐orbitals are expected to be larger. Moreover, it has been shown by Curti et al that the electron lone‐pair of bismuth is located in the direction toward the basal planes of the Mn 3+ O 5 ‐pyramids, which could also support the hopping of electrons along b . The anisotropy of the elastic constants (sound velocities) is another consequence of this enhanced interaction since the a ‐direction was found to be significantly softer than b or c …”