The physical and photo electrochemical characterization of the crednerite CuMnO sub(2)

• Published in: Journal of materials science 2007-08, Vol.42 (15), p.6469-6476
• Main Authors: Bessekhouad, Yassine, Gabes, Yamina, Bouguelia, Aissa, Trari, Mohamed
• Format: Article
• Language: English
• Subjects: Chlorides; Copper; Insertion; Materials science; Orbitals; Oxides; Polyhedrons; Yttrium
• ISSN: 0022-2461
• DOI: 10.1007/s10853-006-1250-x

CuMnO sub(2) is prepared via Cu super(+) 1 Li super(+) exchange in molten copper (I) chloride. It crystallizes in a monoclinic structure (SG C2/m) where the MnO sub(6) octahedra elongation is ascribed to the Yahn-Teller (Y-T) effect of Mn super(3+) ions. From chemical analysis, the oxide is more accurately formulated as CuMnO sub(2.01). Above 250 C, it undergoes a reversible transition to spinel Cu sub(x)Mn sub(3-x)O sub(4) and beyond 940 C it converts back to Cu sub(1.1)Mn sub(0.9)O sub(2). Extrapolation of high-temperature magnetic data indicates T-intercept [thetas] sub(p) of -450 K and an effective moment of 5.22 k sub(B), consistent with strong antiferromagnetism in the basal plans and high spin (HS) configuration Mn super(3+). This value is slightly larger than that of the spin only moment, a behavior ascribed to Cu super(2+) originating from oxygen insertion. As prepared, CuMnO sub(2) displays p-type conductivity with an activation energy of 0.16 eV. Most holes generated upon band gap excitation are trapped on Cu super(+) ions and the conduction occurs by small polarons hopping between neighboring sites. The linear increase of thermopower for Cu sub(1.05)Mn sub(0.95)O sub(2) with temperature indicates a hole mobility k sub(300 K) (3.5 x 10 super(-6) cm super(2) V super(-1 )s super(-1)) thermally activated. CuMnO sub(2) is made p- and n-type and the difference in the carriers mobilities is attributed to different oxygen polyhedra. The title oxide, characterized photo electrochemically, exhibits a pH-insensitive flat band potential (+0.13 V sub(SCE)). The valence band, located at 5.3 eV below vacuum, is made up of Cu 3d orbital. As application, the powder showed a good performance for the H sub(2)-photo evolution.