An EXAFS study of the structure of the Zn_1-xBe_xSe alloy system

Zn_1-xBe_xSe is an interesting II-VI semiconductor showing unusual phonon behavior for 0.19<x<0.81which has been ascribed due to presence of chains of Be and Se with two slightly differing Be-Se bond distances. EXAFS data have been recorded for several compositions of Be in this mixed crystals at the Zn and Se K edges and analyzed to determine the nearest and next nearest neighbor distances for Zn and Se atoms as a function of "x". The effects of these chains is observed in the form of an increase in the σ² value of the Be-Se bond at x = 0.42 and 0.55 as compared to smaller "x" values of 0.06, 0.16 and 0.27. Theoretical estimates show that the bond length difference between the two Be-Se bonds is ∼ 0.04Å, which seems to be too small to be resolved as two different bond lengths but could be observed only as increase in σ² value for larger values of "x". The trends in the various bond angles as a function of "x" have also been explained in terms of the distorted tetrahedral structure in the ternary.