Investigations on synthesis and electrical properties of the La_1.75Nd_0.1Ce_0.15CuO_3.5 prepared by topotactic reduction with CaH₂

Abstract

This paper reports the reaction of a cuprate La_1.75Nd_0.1Ce_0.15CuO₄ with CaH₂ which yields La_1.75Nd_0.1Ce_0.15CuO_3.5, 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 La_1.75Nd_0.1Ce_0.15CuO_3.5 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 (CuO_1.5□_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 La_1.75Nd_0.1Ce_0.15CuO_3.5 phase to T’-La_1.75Nd_0.1Ce_0.15CuO₄. 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.

GRAPHICAL ABSTRACT

Keywords:

• Non-stoichiometric oxides
• reduction via hydride method
• oxygen mobility
• electron paramagnetic resonance
• electrical properties
• equivalent circuits

Disclosure statement

No potential conflict of interest was reported by the reported by the author(s).