Abstract
AbstractA detailed theoretical study of the effects of force constant changes as well as defect concentration on localized vibrational mode frequencies observed in dilute copper alloys is made after employing a localized perturbation model which includes the change in mass at the impurity site as well as the change in nearest neighbour central force constant. The force constant change, when calculated after considering exactly the effects of impurity concentration c in single site approximation, is found to be appreciably different from that calculated in very low concentration approximation (c → 0). An effective force constant, described in the framework of a nearest neighbour rigid‐ion model of lattice dynamics, is calculated in a self consistent manner and utilized to study its frequency dependence. The force constant changes introduced explicitly by volume effects due to impurity atoms are evaluated in a way which does not involve any arbitrary parameter. The experimentally measured inband‐phonon shifts in a Cu‐4.1% Al alloy are described well by the calculated force constant change.
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