Etude ab initio du mécanisme microscopique des transitions reconstructives dans les binaires de type B3.

Abstract

Using an ab initio calculation, we show in this work that we can easily simulate the reconstructive phase transition mechanism B3B1 generated by the application of a hydrostatic pressure to binary compounds. We use an intermediate state (Imm2) with orthorhombic form. We have relied the parent phases by means of a groupsubgroup relationship. The choice of sub-group is not born by chance but through the computation of local constraints along the transformation path. The intermediate phase Imm2 has been simulated in the binary by a sol coordinate at the z position of the cation. The transition path generates a decrease in the volume due to the change of the two structural ratios c /a and b/ a. The tolerance parameter of the deformation being minimal; the phase transition of both binaries compounds need a minimum activation energy. The curve of the transition path gave a smooth and well symmetrical shape. Our activation barriers, calculated using the martensitic approach, show that the ionic CuBr needs a very small energy to undergoes from the semiconductor state to the metallic state (B1). Whereas, the GaAs compound, requires 10 times more energy to undergoes this transition.