Influence of synthesis procedure on the formation of RuO 2 S. Music ´ a, * , S. Popovic ´ b , M. Maljkovic ´ a , K. Furic ´ a , A. Gajovic ´ a a Rud ¯er Bos ˇkovic ´ Institute, P. O. Box 180, 10002 Zagreb, Croatia b Department of Physics, Faculty of Science, University of Zagreb, P.O. Box 331, 10002 Zagreb, Croatia Received 8 February 2002; accepted 10 February 2002 Abstract The influence of synthesis procedure on the formation of RuO 2 was examined. The synthesis applied in the present work was based on the addition of strong organic alkali (tetramethylammonium hydroxide (TMAH)) into alcoholic or water solution of RuNO(NO 3 ) 3 and the precipitation of amorphous ruthenium hydrous oxide, which was further heated at high temperatures. The synthesis conditions for the preparation of nanocrystalline RuO 2 , as a single phase, were found. XRD showed that amorphous ruthenium hydrous oxide, upon thermal treatment, easily transforms into RuO 2 and Ru. The molar fractions of these two phases depended on the heating temperature and atmosphere (air or argon). The samples were also characterized by laser Raman and Fourier-transform infrared (FT-IR) spectroscopies. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Synthesis; RuO 2 ; Alkali 1. Introduction The present-day interest in the chemistry of ruthe- nium dioxide, RuO 2 , is primarily due to the existing or possible applications of this material in advanced technologies. The chemistry of RuO 2 is more complex than that of many other metal oxides. The reason is very simple; ruthenium easily changes the oxidation numbers in dependence on the experimental condi- tions [1]. A change in oxidation number also influen- ces the adsorption/desorption properties of ruthenium [2–4] and the separation of radioactive ruthenium from the cyclotron target [5]. Several methods are known for the preparation of RuO 2 . Ma ´lek et al. [6] precipitated Ru(OH) 3 from acidic RuCl 3 solution at pH f 3 to 5.5 using NH 4 OH as a precipitating agent. Ru(OH) 3 was unstable and oxidized to RuO 2 ÁxH 2 O in air. Upon thermal treat- ment of RuO 2 ÁxH 2 O at a temperature above 300 jC, the crystallization of RuO 2 took place. Duvigneaud and Reinhard-Derie [7] assumed the composition Ru(OH) 3 ÁH 2 O of the precipitate prepared from dea- erated RuCl 3 solution using NH 4 OH as a precipitating agent at pH 8.5. A sharp exothermic peak at 370 jC in air was recorded due to RuO 2 crystallization. The sample removed from DTA furnace at this temper- ature showed an XRD pattern of the rutile-type RuO 2 . RuO 2 nanorods were prepared using carbon nano- tubes as template [8]. McKeown et al. [9] investigated the structure of ruthenium hydrous oxide. Ruthenium hydrous oxides, for example RuO 2 ÁxH 2 O or RuH x O y , exhibited a mixed electron – proton conductivity [10], whereas the anhy- drous rutile-type RuO 2 is a metal-like conductor. 0167-577X/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0167-577X(02)00618-3 * Corresponding author. E-mail address: music@rudjer.irb.hr (S. Music ´). www.elsevier.com/locate/matlet November 2002 Materials Letters 56 (2002) 806 – 811