THERMAL TRANSFORMATIONS OF THE COMPOSITION AND STRUCTURE OF HEXAGONAL MOLYBDENUM OXIDE
I. B. Troitskaia1, T. A. Gavrilova1, A. P. Zubareva2, D. Yu. Troitskii2, S. A. Gromilov2,3
1Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
2Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
3Novosibirsk National Research State University, Novosibirsk, Russia
Keywords: molybdenum oxide, metastable phase, structural water, hygroscopic crystals, crystal texture
Abstract
Thermal transformations of the crystal structure and composition of the h-MoO3 metastable phase with a transition to the α-МоО3 stable modification are investigated. The study is performed using submicron phase-pure crystals exhibiting stability during their long storage in the air. By powder XRD, SEM, TGA, CHN, LMS, Raman and IR spectroscopy it is found: the composition of the deposited crystals is expressed by the general formula МоО3·0.26H2O; the impurity cationic composition consists of 1.8 wt.% of ammonia groups and a sum of 15 elements detected at a level of 10–4 wt.%. Thermal treatment of the crystals to T = 350 °C in the air results in the removal of adsorbed and structural water, ОН–, and NH4+ groups with retaining the h-phase of hygroscopic МоО3·0.08H2O. The h-МоО 3·0.08H2O crystals obtained show instability during the storage and transform into the α-МоО3 stable modification. At T = 380 °C the h → a phase transition occurs with the removal of coordinated water and texture transformations resulting in the formation of α-МоО 3 hygroscopic crystals that at T = 650 °C acquire the platelet shape characteristic of the α-phase.
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