Abstract
Calculated far-IR lattice absorption due to a small concentration of beryllium impurities in cubic zinc sulphide has been reported for the first time. The method of calculation follows the Green's function technique. The evaluation of the involved Green's function for zinc sulphide is made by incorporating the real phonons obtained from a second-neighbor-ionic (SNI) model. A defect model that considers the change of mass at the impurity site as well as the changes in the nearest-neighbor (central and angular interactions) is employed in calculating the absorption and the impurity modes. The experimentally observed IR absorption below 100 cm −1 can be understood only if one takes into account the changes in the angular force constants around the impurity. The calculated absorption is compared and discussed with the existing experimental data.
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