Characterization of crednerite-Cu1.1Mn0.9O2 films prepared using sol-gel processing

In this study, pure crednerite-Cu1.1Mn0.9O2 films were deposited onto quartz substrates using a sol-gel processing and a two-step annealing process. The sol-gel-derived films were annealed at 500 °C for 1 h in air and post-annealed at 600-700 °C for 2 h in N2. X-ray diffraction patterns showed that the films were CuO and CuxMn3 − xO4 phases in air annealing. When the films were post-annealed above 600 °C in N2, a pure CuMnO2 phase with the monoclinic crednerite structure (space group: C2/m) was obtained. The lattice parameters of the crednerite-Cu1.1Mn0.9O2 films where a = 0.5579-0.5587 nm, b = 0.2878-0.2881 nm, c = 0.5880-0.5891 nm, and β = 104.16-104.34° and were agreement with the literature reports. The binding energies of Cu-2p of the crednerite-Cu1.1Mn0.9O2 films were 932.3 ± 0.2 eV and 952.3 ± 0.2 eV to represent the monovalent Cu in the films. Additionally, the binding energies of Mn-3p of the crednerite-Cu1.1Mn0.9O2 films were 47.5 ± 0.2 eV, 48.2 ± 0.2 eV, and 50.0 ± 0.2 eV and revealed coexistence of +2, +3, and +4 valences in the films. The cation distributions of the crednerite-Cu1.1Mn0.9O2 films prepared using post-annealing at 650 °C and 700 °C were Cu+1.1[Mn4+0.25Mn3+0.51Mn2+0.24]0.9O2 and Cu+1.1[Mn4+0.24Mn3+0.52Mn2+0.24]0.9O2, respectively. Two optical bandgaps of the crednerite-Cu1.1Mn0.9O2 films at 4.5-4.0 eV and 3.5-3.0 eV were observed. The electrical conductivities of the crednerite-Cu1.1Mn0.9O2 films were 1.20 × 10−5-2.50 × 10−5 S cm−1. Moreover, the activation energies for the carrier conduction were 0.20-0.30 eV. Hence, our results demonstrate that sol-gel processing is a feasible preparation method for crednerite-CuMnO2 films.