Quantum-chemical study of stable, meta-stable and high-pressure alumina polymorphs and aluminum hydroxides

Abstract

The structure, properties and stability of 7 thermodynamically stable, meta-stable and high-pressure Al2O3 polymorphs and the structure and relative stability of 4 Al hydroxides were calculated with periodic hybrid density functional theory and compared with available experimental data.

Critical Review—Photocurrent Spectroscopy in Corrosion and Passivity Studies: A Critical Assessment of the Use of Band Gap Value to Estimate the Oxide Film Composition

“…In the case of Al 2 O 3 , the E g values experimentally measured (or derived by DFT studies) for different polymorphs span a quite large range of energies 41 well outside the range of energies (5.5-6.40 eV) derived by using Eq. 3b and the uncertainty in the electronegativity parameter of the cation (χ Al = 1.5 ± 0.05).…”

“…This last value is in good agreement with the experimental E g,opt values (6.0-6.2 eV) measured for amorphous alumina anodic barrier film 74 and Atomic Layer Deposition films 75 as well as with the theoretical estimated value of the spinel phase γ-Al 2 O 3 . 41 As mentioned above, a limited variation of the E g values can be easily accommodated by using the range of uncertainty embodied in the Pauling scale of electronegativity, whilst the large variation in the E g values of the different polymorphs of Al 2 O 3 requires, in our opinion, a different approach which takes into account possible changes in the value of A and B.…”

“…We are aware that reasonable changes in the R values cannot always account for the differences in the reported or estimated bandgap values of several polymorphs, 41 and that changes in the A value of the employed correlation can be also necessary (see below for α-(Ga x Al 1-x ) 2 O 3 ).…”

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.…”

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

“…Hence, unraveling the rates and mechanisms of Al metal reactivity with O2 in fine powders, nanoparticles, thin films, and molecular clusters has been the subject of considerable experimental [2][3][4][5][6][7] and theoretical effort. [8][9][10][11][12][13] Understanding how changes in the phase of Al2O3 can impact reactivity has important consequences for scientific and technological applications for aluminum in ceramics, catalysis, coatings, separations, [14][15][16][17][18][19][20] and energetic materials. [21][22][23][24][25] To optimize the synthesis of well-defined nanoparticles and control their reactivities, characterization tools are needed that can probe the structure of heterogenous materials over multiple length scales and under real-world conditions.…”