Journal of Alloys and Compounds 509 (2011) 2933–2935 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Synthesis of nanosized CuCrO 2 porous powders via a self-combustion glycine nitrate process Te-Wei Chiu ∗ , Bing-Sheng Yu, Yuh-Ruey Wang, Kun-Te Chen, Yu-Te Lin Department of Materials and Mineral Resources Engineering, National Taipei University of Technology, 1, Sec. 3, Zhongxiao E. Rd., Taipei 106, Taiwan article info Article history: Received 27 October 2010 Received in revised form 21 November 2010 Accepted 23 November 2010 Available online 30 November 2010 Keywords: Oxide materials Delafossite CuCrO2 Glycine nitrate process abstract The glycine nitrate process has been successfully employed to prepare nanosized, porous, stoichiomet- ric, homogeneous CuCrO 2 powders without ambient control. In this method, a precursor solution was prepared by mixing glycine with an aqueous solution of blended (Cu–Cr) metal–nitrates in their stoi- chiometric ratios. The glycine-mixed precursor solution was first heated in a beaker to evaporate excess water for forming a viscous bluish semi-transparent gel. The beaker was then covered with a metallic mesh, and the temperature increased slowly to 170 ◦ C to auto-ignite the material. The combustion was self-sustaining and very rapid, producing gray colored powders. The as-prepared powders were nano- sized (∼20 nm) into a spherical shape and crystallized in a delafossite structure. The powders showed a very large surface area of 30.92 m 2 /g, as determined by BET surface area measurements. The SEM/TEM studies on these powders confirmed their nanosized nature and porous structure. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Delafossite CuCrO 2 has attracted much attention as a p-type transparent conductive oxide (TCO), which is of great interest for several applications such as transparent diodes and solar cells [1–3]. Related studies on delafossite oxides are interested not only in examining the TCOs properties but also in exploring their appli- cations as photo catalysts for hydrogen evolution [4] and NO 2 removal [5], catalysts for steam reforming process [6] and exhaust gas purification [7], room temperature ozone sensors [8], magnetics [9], and thermoelectric devices [10]. One way to improve the catalysis efficiency is to decrease the size of the catalyst in order to increase the surface area and adsorp- tion ability. Synthesizing nanosized CuCrO 2 powder can therefore be expected to improve the performance of catalytic applications, and controlling the valence state of Cu to 1 + is the key to success- ful synthesis of CuCrO 2 . According to the isobaric phase diagram of the bulk Cu 2 O–Cr 2 O 3 –CuO ternary system reported by Jacob et al. [11], when CuO and Cr 2 O 3 react in air, CuO and Cr 2 O 3 favorably react to form spinel-type CuCr 2 O 4 at 700 ◦ C. Pure delafossite-type CuCrO 2 is converted from spinel-type CuCr 2 O 4 with residual CuO above 1000 ◦ C. The chemical formulae are shown in (1) and (2): 2CuO + Cr 2 O 3 → CuCr 2 O 4 + CuO (1) CuCr 2 O 4 + CuO → 2CuCrO 2 + 1/2O 2 (2) ∗ Corresponding author. Tel.: +886 2 2771 2171; fax: +886 2 2731 7185. E-mail address: tewei@ntut.edu.tw (T.-W. Chiu). According to formula (2), the reducing atmosphere helps obtain the CuCrO 2 phase thermodynamically. Thus, to synthesize CuCrO 2 under a relatively low temperature, an oxygen-free atmosphere, such as argon gas, is required [3,12]. Nanoparticles of CuCrO 2 have been synthesized by hydrother- mal [13] and citric acid methods [14]. Although the glycine nitrate process (GNP) is very widely applied to synthesize homogeneous single, binary, and multicomponent oxide systems, it has not been employed to synthesize copper–chromite solid solutions. There- fore, the goal of the present investigation is to determine the utility and usefulness of GNP in producing CuCrO 2 nanopowders with a high surface area. CuCrO 2 with a typical composition and a delafos- site structure was used in the present investigation. The results of the synthesis and characterization of CuCrO 2 nanopowders are reported and discussed in this paper. 2. Experimental 2.1. Synthesis of CuCrO2 powders 2.1.1. Solid state reaction In order to compare the characteristics of CuCrO2 powder prepared by the GNP method to those of traditional CuCrO2 powder, CuCrO2 powder was also prepared by traditional solid state reaction method. The Cu2O and Cr2O3 powders were used as starting materials. These powders were mixed with ethanol in a plastic jar with zirconia balls and milled for 24 h. The resulting slurries were dried at 70 ◦ C in an oven. The dried powders were calcined in a crucible at 1200 ◦ C for 6 h in air. 2.1.2. GNP method For the synthesis of CuCrO2 powders by GNP route, copper nitrate [Cu(NO3)2·3H2O], chromium nitrate [Cr(NO3)3·9H2O], and glycine were used as starting reagents. Copper nitrate, chromium nitrate, and glycine of required amounts 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.11.162