Low temperature Raman spectroscopic study of scandium molybdate

Abstract

Low temperature Raman spectroscopic measurements are carried out onSc2(MoO4)3 to probe the orthorhombic–monoclinic phase transition. Phonon frequencies and theirtemperature coefficients are found to change discontinuously across the transition. Several modesare found to disappear while some new modes appear across the transition. The evolutionof intensities of the modes suggests a two-phase coexistence over a temperature interval ofabout 20 K both in the cooling and heating cycles. The transition is found to occur at142 ± 10 K upon cooling while the reverse transition occurs at174 ± 11 K during the heating cycle, i.e., the system exhibits a hysteresis of 32 K. Incontrast to the usual behaviour, most of the phonon modes in the monoclinicphase exhibit softening upon further cooling. Separation of the temperaturedependence of Raman mode frequencies into quasi-harmonic and purely anharmoniccontributions using reported high pressure Raman data reveals that bending modes ofMoO4 ions are the most anharmonic among the modes studied.