Optical and electrical properties of the delafossite CuCrO2 synthesized by co-precipitation

CuCrO2 was successfully prepared by co -precipitation from nitrates precursors under N-2 atmosphere. The X-ray diffraction pattern is characteristic of a single phase indexed in a rhombohedral symmetry with 3R polytype (Space Group: R3m). Thermogravimetric study showed a stability up to 900 degrees C with a high electrostatic energy. SEM image shows the formations of grains with regular shapes with average sizes (0.5-1 mu m). A direct optical transition at 2.49 eV, determined from the diffuse reflectance, is assigned to internal d -d transition by lifting degeneracy of Cu+: 3d orbital in linear crystal field. The electrical conductivity is thermally activated, and characteristic of a non -degenerate semiconductor; it follows an exponential law: sigma = sigma(o) exp{-0.13 eV/k(beta)T (Omega-cm)(-1)} with a mechanism conduction by low polaron hopping (LPH) between mixed valences Cu2+/+ in the (0 0n) planes. The high energy (E-a) implies that both the density (N-A) and a mobility (mu(h)) thermally activated. The hopping occurs over crystallographic sites between mixed states Ag2+/+. The holes doped oxide is assigned to low polaronic Cu2O units, the conduction of which gives a mobility of 1.04 x 10(-4) cm(2) V-1 s(-1). The p type comportment of CuCrO2 is supported by the negative slope of the linear Mott -Schottky plot where a hole density of 1.43 x 10(17) cm(-3) and a flat band potential of 0.21 V-SCE are extracted. This leads to a valence deriving from Cu+-3d character (5.09 eV, 0.34 V-SCE).