Infrared spectra from solid solutions of spessartine and yttrium aluminum garnet

Compositional relationships were established through thin-film spectroscopy for all 17 infrared lattice vibrations in compositions along the binary join spessartine Mn₃Al₂Si₃O₁₂ - yttrium aluminum garnet Y₃Al₂Al₃O₁₂. Thin-film frequencies of the end members are in excellent agreement with transverse optic modes obtained from single-crystal reflectance spectra. All but a few weak modes are traceable completely across the binary, such that most frequencies depend almost linearly on cell parameters. Different behaviors are seen for the modes assigned to various atomic motions. Frequencies of the dodecahedral translations increase very slightly, indicating that the increase in average mass as Y³⁺ replaces Mn²⁺ is offset by the increase in bond strength as average valency increases. -from Authors