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Compositions of polycrystalline Zn x Mg 1-x Fe 2-y Nd y O 4 (x = 0⋅ ⋅00, 0⋅ ⋅20, 0⋅ ⋅40, 0⋅ ⋅60, 0⋅ ⋅80 and 1⋅ ⋅00; y = 0⋅ ⋅00, 0⋅ ⋅05 and 0⋅ ⋅10) ferrites were prepared by standard ceramic method and characterized by X-ray diffraction, scanning electron microscopy and infrared absorption spectroscopy. Far infrared absorption spectra show two significant absorption bands, first at about 600 cm-1 and second at about 425 cm-1 , which were respectively attributed to tetrahedral (A) and octahedral (B) sites of the spinel. The positions of bands are found to be composition dependent. The force constants, K T and K O , were calculated and plotted against zinc concentration. Compositional dependence of force constants is explained on the basis of cation-oxygen bond distances of respective sites and cation distribution.

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