Investigations on synthesis and electrical properties of the La1.75Nd0.1Ce0.15CuO3.5 prepared by topotactic reduction with CaH2

Abstract

This paper reports the reaction of a cuprate La1.75Nd0.1Ce0.15CuO4 with CaH2 which yields La1.75Nd0.1Ce0.15CuO3.5, a new oxygen-vacancy-ordered arrangement of cooperatively-distorted Cu2O3 planes containing four-coordinate Cu+ sites. This new compound has been characterized by X-ray diffraction, electron paramagnetic resonance (EPR), differential scanning calorimetry (DSC) and impedance spectroscopy. The powder X-ray diffraction data have shown that La1.75Nd0.1Ce0.15CuO3.5 adopts a face-centered monoclinic crystal structure (A2/m, a = 8.6216(6), b = 3.8452(3) Å, c = 13.0157(12) and β = 109.691(2)°) with anion vacancies located within the CuO2 (CuO1.5□0.5, where □ represents an anion vacancy) layer of the phase. The EPR measurements have shown the presence of Cu2+ and a hyperfine structure suggesting a pronounced hybridization of the copper-oxygen bond. The impedance spectra were analyzed in terms of equivalent circuits involving resistors, capacitors and constant phase elements (CPE). The re-oxidization under mild conditions at 420 °C in oxygen atmosphere transforms La1.75Nd0.1Ce0.15CuO3.5 phase to T’-La1.75Nd0.1Ce0.15CuO4. This phase transition is confirmed by DSC and impedance spectroscopy. The significance of this reaction relates to its mechanism, as it implies low temperature oxygen mobility realized in a solid oxide, which has technological importance for oxygen membranes of SOFCs.