UNCORRECTED PROOF MAC 11030 1–4 Materials Chemistry and Physics xxx (2005) xxx–xxx Review Low temperature Ce 2 Si 2 O 7 polymorph formed by mechanical activation 3 4 S. Zec ∗ , S. Boˇ skovi´ c, ˇ Z. Bogdanov, N. Popovi´ c 5 Institute of Nuclear Sciences Vinˇ ca, 11001 Belgrade, P.F. 522, Serbia and Montenegro 6 Received 26 April 2005; accepted 20 May 2005 7 Abstract 8 Studying solid state reaction between mechanically activated oxide powders of CeO 2 and quartz-SiO 2 , we obtained directly during heat treatment, the low temperature polymorph of Ce 2 Si 2 O 7 instead of the high temperature polymorph formed in non-activated oxides mixture. The mixture with composition corresponded to Ce 2 Si 2 O 7 stoichiometry was mechanically activated by milling in high energetic vibratory mill for 2–120 min. Heating was done in an Astro furnace in a flowing argon atmosphere at 1200–1550 ◦ C for 1 h while the specimens were furnace cooled. Crystallite size, lattice distortion and phases identification was performed by X-ray powder diffraction (XRD) analysis. Microstructure characterization of the mixtures was done using scanning electron microscopy (SEM). Low temperature polymorph of Ce 2 Si 2 O 7 was obtained in activated mixtures at temperatures below 1400 ◦ C. 9 10 11 12 13 14 15 © 2005 Published by Elsevier B.V. 16 Keywords: Inorganic compounds; Phase transitions; Powder diffraction; Crystal structure 17 18 Contents 1. Introduction .......................................................................................................... 00 2. Experimental procedure ............................................................................................... 00 3. Results and discussion ................................................................................................. 00 4. Conclusions .......................................................................................................... 00 Acknowledgment ..................................................................................................... 00 References ........................................................................................................... 00 1. Introduction 19 Recently, interest in cerium silicates investigation has 20 increased because of their diverse properties. These com- 21 pounds could have many applications in optoelectronics, 22 microelectronics, catalysis, etc. [1,2]. While the tetrava- 23 lent cerium does not form silicates, trivalent cerium forms 24 three compounds: Ce 2 SiO 5 , Ce 4.67 (SiO 4 ) 3 O and Ce 2 Si 2 O 7 . 25 Heated in air, these silicates are not stable and decompose ∗ Corresponding author. Tel.: +381 11 2439 454; fax: +381 11 2439 454. E-mail address: zec@vin.bg.ac.yu (S. Zec). 26 into CeO 2 and SiO 2 due to oxidation of cerium. Ce 2 Si 2 O 7 , 27 cerium disilicate or pyrosilicate, was found to have two 28 polymorphic modifications, the low temperature polymorph 29 with tetragonal crystal structure (A type) and the high tem- 30 perature monoclinic modification (G type). If the conven- 31 tional solid state reaction between oxide powders is per- 32 formed for Ce 2 Si 2 O 7 synthesis, the low temperature poly- 33 morph can be obtained only by annealing the high temper- 34 ature modification of Ce 2 Si 2 O 7 . The sluggish phase tran- 35 sition was found to occur at 1274 ◦ C [3]. However, using 36 the spray drying technique starting with solutions as the 37 cerium and silicon precursors, the low temperature form 38 1 0254-0584/$ – see front matter © 2005 Published by Elsevier B.V. 2 doi:10.1016/j.matchemphys.2005.05.036