Influences of post-annealing conditions on the formation of delafossite-CuFeO2 thin films

In this study, post-annealing conditions, the partial oxygen pressures (pO(2)) and temperatures, influence on the formation of delafossite-CuFeO2 thin films is studied. The sol-gel derived films were annealed at 500 degrees C in air and post-annealed at 500-850 degrees C in pO(2) = 10(-2) to pO(2) = 5 x 10(-5) atm. The CuO and CuFe2O4 phases appeared when the sol-gel derived films were post-annealed below 800 degrees C for 2h in pO(2) = 10(-2) atm, 650 degrees C for 2h in pO(2) = 10(-3) atm, and 550 degrees C for 2h in pO(2) = 5 x 10(-5) atm. Pure delafossite-CuFeO2 phase was detected as specimens were post-annealed above 800 degrees C for 12h in pO(2) = 10(-2) atm, 650 degrees C for 12h in pO(2) = 10(-3) atm, and 550 degrees C for 12h in pO(2) = 5 x 10(-5) atm. The surface of post-annealed thin films exhibited a nanoparticle-like morphology when the specimens exhibited CuO and CuFe2O4 phases. However, the surface revealed granular features caused by the formation of the delafossite-CuFeO2 phase. The formation of the delafossite-CuFeO2 phase, which resulted from the chemical reaction of the CuO and CuFe2O4 phases in the post-annealing process, is consistent with thermodynamics. The optical bandgaps of delafossite-CuFeO2 thin films prepared using post-annealing ranged between 3.1 and 3.2 eV. The electrical conductivities of delafossite-CuFeO2 thin films were (1.62-6.37) x 10(-1) S cm(-1) and the carrier concentrations were (1.52-8.84) x 10(17) cm(-3). The pO(2) and temperatures in the post-annealing process played primary roles in the formation of delafossite-CuFeO2 thin films in this study. (C) 2013 Elsevier B.V. All rights reserved.