Ab initio27Al NMR chemical shifts and quadrupolar parameters for Al2O3phases and their precursors

Abstract

The Gauge-Including Projector Augmented Wave (GIPAW) method, within the Density Functional Theory (DFT) Generalized Gradient Approximation (GGA) framework, is applied to compute solid state NMR parameters for 27 Al in the α, θ, and κ aluminium oxide phases and their gibbsite and boehmite precursors. The results for well-established crystalline phases compare very well with available experimental data and provide confidence in the accuracy of the method. For γ-alumina, four structural models proposed in the literature are discussed in terms of their ability to reproduce the experimental spectra also reported in the literature. Among the considered models, the F d3m structure proposed by Paglia et al. [Phys. Rev. B 71, 224115 (2005)] shows the best agreement. We attempt to link the theoretical NMR parameters to the local geometry. Chemical shifts depend on coordination number but no further correlation is found with geometrical parameters. Instead our calculations reveal that, within a given coordination number, a linear correlation exists between chemical shifts and Born effective charges.

Theoretical studies of the interaction of terephthalate anion in MgAl-layered double hydroxides

“…The chemical shielding tensors (σ) were calculated using gauge-including projector augmented waves (GIPAW). This method was based on DFT to calculate magnetic resonance properties, exploiting the full translational symmetry of crystals (Pickard & Mauri, 2001), (Yates et al, 2007), (Ferreira et al, 2011). Interaction of valence electrons with nuclei and core electrons is treated by the projector augmented-wave (PAW) method.…”

Assessing thermochemical properties of materials through ab initio quantum-mechanical methods: the case of α-Al2O3

“…Several computational studies on aluminum oxide polymorphs have been reported in recent years, which mainly apply standard DFT methods. [22][23][24][25][26][27][28][29][30] In this paper, we apply a recently developed technique based on the so-called quasi-harmonic approximation (QHA): a simple and effective method that is able to address the aforementioned issue in the case of corundum. 31,32 The thermal expansion coefficient, α(T ), heat capacities, C V (T ) and C P (T ), entropy, S(T ) and bulk modulus, K(T ) of corundum are calculated in its entire range of thermal stability (i.e.…”

Diffusion of oxygen in amorphous Al2O3, Ta2O5, and Nb2O5

“…The structure of a-Al 2 O 3 has been actively discussed from the short-and medium-range point-of-view by x-ray photoelectron 12,13 and Auger electron 12 spectroscopy, extended x-ray absorption fine structure technique, 14 transmission electron microscopy, 15,16 nuclear magnetic resonance spectroscopy, 17 and also by a number of theoretical approaches. [18][19][20][21][22] On the other hand, few studies have been reported for a-Ta 2 O 5 and a-Nb 2 O 5 . [23][24][25] In this study, the diffusivity of the common element, oxygen, in a-Al 2 O 3 , a-Ta 2 O 5 , and a-Nb 2 O 5 was investigated.…”