Abstract
Boron arsenate, BAsO4, is crystalline material (I4¯ group) that was recently shown to be auxetic in its (001) plane for loading in any direction in this plane, and, which exhibits negative linear compressibility at elevated pressured in its [001] direction. This work presents and discusses the results of extensive density functional theory (DFT) based simulations aimed at studying deformations that such crystals undergo when subjected to shear loading in an attempt to obtain a better insight into the manner in which this material responds to mechanical loads. The deformations for shearing in the (001) plane are described in terms of the ‘rotating squares’ model, which was used to explain the auxeticity in the same plane where it was shown that shear loading results primarily in deformations which make the ‘squares’ become ‘parallelogram-like’ rather than rotate. This lack of rigidity in projected ‘squares’ was discussed by looking at changes in bond lengths and bond angles.
Highlights
Symmetry 2021, 13, 977. https://Boron arsenate, BAsO4, see Figure 1, is a spectacular material having both a history and a prehistory, in terms of its synthesis and crystal properties
Boron arsenate was not characterized and no particulars were given for the synthesis of the compound, as it was not the scope of their study, in which it was used as a reducible compound to form arsenic vapours
The single crystal of boron arsenate with its standard I4 symmetry reduced to P1 was aligned within the global coordinate system according to the convention adopted by the Institute of Radio Engineers (IRE) [71], i.e., in a manner that the [001] crystal direction is parallel to the global z-axis and the [010] crystal direction is aligned in the global yz-plane with no constraints being placed on the [100] direction
Summary
BAsO4 , see Figure 1, is a spectacular material having both a history and a prehistory, in terms of its synthesis and crystal properties. Schulze’s method for the synthesis of the crystal, was described in a later publication the following year as a solid state reaction between arsenic oxide (As2 O5 ) and boron trioxide (B2 O3 ) at high temperature [2]. This paper will look at a different aspect in BAsO4 namely, from the perspective of its mechanical properties and will focus on the atomic level deformations that occur when this material, as a single crystal, is subjected to mechanical loads Such a perspective is important in view of the anomalous negative Poisson’s ratio (auxetic) [11,12] and negative linear compressibility characteristics [12,13], properties it shares with a number of other anomalous materials, models and structures. The theoretical framework required to study crystals in this manner is well established and explained in detail elsewhere [69]
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