EXAFS data resolved into individual site occupation preferences in quaternary compounds with tetrahedral coordinated structure

Site-occupation preferences (SOPs) in quaternary GaxIn1-xAsySb1-y and Cd1-xMnxSeyTe1-y compounds in tetrahedrally coordinated (T-C) zinc blende (ZB) structures are discussed, where x and y are the relative contents' of cations and anions, respectively. A probabilistic approach defines individual component pair-populations from measured average-pair distributions. Particular attention is paid to the T-C ZB-structure. The methodology and interpretation of SOPs of published extended X-ray absorption fine structure (EXAFS) experimental data for overall average-pair distributions are discussed. The approach allows definition of component individual T-k-pair site-occupation populations and deeper insight into the selective processes that cause individual poir preferences in semiconducting multinary compounds. EXAFS-reported departures from Bernoulli random distributions point to changes within elemental tetrahedral average populations. Resolution requires that for T-C-structures, experimental data best fit be a 4th degree polynomial, the product of a parabola times the Factor x(1-x). Analysis shows that GaInAsSb and CdMnSeTe have a marked preference for elemental tetrahedra with odd numbers of competing species of ions around a central ion, and that the former exhibits SOPs of 2.19+/-0.2 and 1.63+/-0.11 for elemental tetrahedra with respectively 1 and 3 Ga-ions around As-ions, and the latter, a SOP of 1.9+/-0.11 for 1Mn3Cd-ions around Se-ion configurations, with respect to the random case. (C) 1999 Elsevier Science S.A. All rights reserved.