BARC/PUB/2016/0616

 
 

First-principles characterisation of the pressure-dependent elastic anisotropy of SnO2 polymorphs

 
     
 
Author(s)

Das, P. K.; Chowdhury, A.; Mandal, N.; Arya, A.
(MSD)

Source

Philosophical Magazine, 2016. Vol. 96 (18): pp. 1861-1882

ABSTRACT

Using DFT calculations, this study investigates the pressuredependent variations of elastic anisotropy in the following SnO2 phases: rutile-type (tetragonal; P42/mnm), CaCl2-type (orthorhombic; Pnnm)-, α-PbO2-type (orthorhombic; Pbcn)- and fluorite-type (cubic; Fm-3m). Experimentally, these polymorphs undergo sequential structural transitions from rutile-type → CaCl2-type → α-PbO2-type → fluorite-type with increasing pressure at 11.35, 14.69 and 58.22 GPa, respectively. We estimate the shear anisotropy (A1 and A3) on {1 0 0} and {0 0 1} crystallographic planes of the tetragonal phase and (A1, A2 and A3) on {1 0 0}, {0 1 0} and {0 0 1} crystallographic planes of the orthorhombic phases. The rutile-type phase shows strongest shear anisotropy on the {0 0 1} planes (A2 > 4.8), and the degree of anisotropy increases nonlinearly with pressure. In contrast, the anisotropy is almost absent on the {1 0 0} planes (ie A1 ~ 1) irrespective of the pressure. The CaCl2-type phase exhibits similar shear anisotropy behaviour preferentially on {0 0 1} (A3 > 5), while A1 and A2 remain close to 1. The α-PbO2-type phase shows strikingly different elastic anisotropy characterised by a reversal in anisotropy (A3 > 1 to < 1) with increasing pressure at a threshold value of 38GPa. We provide electronic density of states and atomic configuration to account for this pressure-dependent reversal in shear anisotropy. Our study also analyses the directional Young’s moduli for the tetragonal and orthorhombic phases as a function of pressure. Finally, we estimate the band gaps of these four SnO2 phases as a function of pressure which are in agreement with the previous results

 
 
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