Polycrystalline Mg_xAl_2xLi_0.5(1−x)Fe_2.5(1−x) O₄ (x = 0.0, 0.2, 0.5, 0.6 and 0.7) ferrites were prepared by standard ceramic method, and characterized by X-ray diffraction and infrared absorption spectroscopy. The spectra show two significant absorption bands in the wave number range of 400–1000 cm⁻¹ arising from interatomic vibrations in the tetrahedral and octahedral coordination compounds. The decrease in intensity and increase in broadness of bands with concentration (x) are explained on the basis of cation distribution. The force constants and bulk modulus are found to decrease with Mg-Al content (x) which suggested weakening of interatomic bonding. An alternate method for the determination of bulk modulus, longitudinal and transverse velocities is suggested. The magnetic and electrical properties of these compounds are explained in the light of structural and optical properties.