Stability of the different AlOOH phases under pressure

Abstract

The pressure effects on three different AlOOH structures (α, γ, and δ phases) are systematically analyzed by density functional theory with different exchange and correlation energy functional approximations, namely two local, two generalized-gradient approximation (GGA), and two GGA for solids (GGAsol). Phase stability, compressibility and hydrogen bond evolution are studied in a range of pressures from 0 to 30 GPa. In general, the use of GGAsol functionals is mandatory in order to have the correct phase stability order, a good description of the hydrogen bonds, and a close agreement with the experimental lattice parameters at the various pressures. Pressure-induced hydrogen-bond symmetrization is found in γ and δ phases at high compression, while the hydrogen bonds in the α phase remain asymmetric. A detailed analysis of the uncertainties on the values of the bulk moduli and their pressure derivative at zero pressure deduced by fitting calculated or experimental (P,V) data is also presented.

Hydrogen bond symmetrization and elastic constants under pressure ofδ-AlOOH

“…As usual, LDA gives lattice parameters that are too short, while PBE gives overly large lattice parameters and a wrong stability sequence of the three phases at low pressures. In contrast, PBEsol and TCAsol give lattice parameters that are in excellent agreement with the experimental data (see table 1), the right phase order and a symmetrization transition pressure (14 GPa for PBEsol, 15 GPa for TCAsol) [12] in close agreement with the value estimated by Sano-Furukawa et al [14] on the basis of neutron diffraction measurements.…”

“…It is interesting to compare the calculated bulk moduli at zero pressure with those reported by Cedillo et al [12]. Their PBEsol bulk modulus is in the range 170-172 GPa and the TCAsol one is between 168 and 170 GPa.…”

“…Tsuchiya and coworkers used the Perdew-Burke-Ernzerhof (PBE) [10] generalized-gradient approximation (GGA) functional, while Panero and Stixrude [11], who performed local density (LDA) calculations, found that the bond is symmetric even at 0 pressure. This conclusion does not seem to be the real LDA prediction, as recent calculations have shown that LDA gives an asymmetric bond at zero pressure [12]. However, the LDA transition pressure is 8 GPa, a value considerably smaller than the PBE one (31 GPa) [12].…”

“…This conclusion does not seem to be the real LDA prediction, as recent calculations have shown that LDA gives an asymmetric bond at zero pressure [12]. However, the LDA transition pressure is 8 GPa, a value considerably smaller than the PBE one (31 GPa) [12]. The symmetrization of the hydrogen bond was briefly discussed also by Li et al [13], who concluded that the transition pressure is smaller than 50 GPa without attempting to evaluate its precise value.…”

“…In a recent paper, Cedillo, Torrent, and Cortona [12] have reported results of DFT calculations for α-, γand δ-AlOOH performed with six different exchange-correlation functionals. They have found that the only ones that give an accurate description of these three AlOOH polymorphs are PBEsol [17] and TCAsol [18,19].…”