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Amorphization and decomposition of scandium molybdate at high pressure

Arora, Akhilesh K. and Yagi, Takehiko and Miyajima, Nobuyoshi and Mary, T. A. (2005) Amorphization and decomposition of scandium molybdate at high pressure. Journal of Applied Physics, 97 (1). Art. no. 013508. ISSN 0021-8979. doi:10.1063/1.1819975.

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The behavior of negative thermal-expansion material scandium molybdate Sc2(MoO4)3 is investigated at high pressure (HP) and high temperature (HT) using x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The compound exhibits unusually high compressibility (bulk modulus ~6 GPa) and undergoes amorphization at 12 GPa. On the other hand, in situ laser heating of amorphous samples inside the diamond-anvil cell is found to result in crystalline diffraction pattern and Raman spectrum different from those of the original compound. Upon release of the pressure subsequent to laser heating, the Raman spectrum and the diffraction pattern remain unchanged. Matching of several of the diffraction lines and Raman peaks in the laser-heated samples with those of MoO3 suggests a solid-state decomposition of the parent compound under HP-HT conditions into MoO3 and other compounds. Other diffraction lines are found to correspond to Sc2Mo2O9, Sc2O3, and the parent compound. Quantitative analysis of the characteristic x-ray emission from different regions of the sample during scanning electron microscopic observations is used for obtaining the compositions of the daughter compounds. The stoichiometries of two main phases are found to be close to those of MoO3 and Sc2Mo2O9. These results support the model that the pressure-induced amorphization occurred in this system because a pressure-induced decomposition was kinetically constrained.

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Additional Information:©2005 American Institute of Physics (Received 29 March 2004; accepted 23 September 2004; published online 13 December 2004) It is a pleasure to thank V. S. Sastry and Dr. R. Nithya for fruitful discussions and F. Sakai for help in SEM that was carried out using the facilities of the Materials Design and Characterization Laboratory, ISSP, University of Tokyo. One of the authors (A.K.A.) acknowledges JSPS for travel support and local hospitality at ISSP, and Photon Factory, KEK for the beam-time and also Dr. B. Viswanathan for interest in the work and Dr. Baldev Raj for support and encouragement.
Subject Keywords:scandium compounds; amorphisation; high-pressure effects; dissociation; high-temperature effects; thermal expansion; elastic moduli; stoichiometry; Raman spectra; X-ray emission spectra; X-ray diffraction; scanning electron microscopy; amorphous state; laser materials processing
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ID Code:1829
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Deposited On:20 Feb 2006
Last Modified:08 Nov 2021 19:42

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