title: Structural origin of the enhanced ionic conductivity upon Nb doping in Sr11Mo4O23defective double perovskite.
abstract: We report a substantial enhancement of the oxide-ion conductivity in Sr11Mo4O23achieved by Nb doping the Mo sites. This series responds to the formula: Sr11Mo4-xNbxO23-δ(with x = 0.0, 0.5 and 1.0). The original structure can be related to the conventional double perovskite; however, it presents a broken corner sharing connectivity of the octahedral framework, hence leading to a complex and highly defective network. The samples were prepared via citrate precursor method, followed by thermal treatments at 1300 °C for 12 hours in air. The crystal structures were refined from X-ray and neutron powder diffraction (NPD) data. A phase transition from tetragonal to cubic symmetry is identified in a temperature-dependent NPD study, driven by an oxygen delocalization effect. The ionic conductivity measured by impedance spectroscopy is enhanced upon Nb-doping; the x = 1 doped phase exhibits a threefold increase compared to the pristine Sr11Mo4O23oxide, with conductivity values of 7.6 × 10-3and 2.7 × 10-2S·cm-1at 650 and 800 °C, which are even greater than for YSZ in the 650-800 °C temperature range, and close to those reported for other state-of-the art solid-oxide electrolytes.
authors.affiliation: INTEQUI, Universidad Nacional de San Luis, CONICET, Área de Química General e Inorgánica "Dr. G.F.Puelles"- Facultad de Química, Bioquímica y Farmacia, Chacabuco y Pedernera, 5700, San Luis, Argentina. calopez@unsl.edu.ar.
authors.forename: C D
authors.identifier: http://orcid.org/0000-0001-5065-7877
authors.initials: CD
authors.lastname: Miranda
authors.affiliation: INTEQUI, Universidad Nacional de San Luis, CONICET, Área de Química General e Inorgánica "Dr. G.F.Puelles"- Facultad de Química, Bioquímica y Farmacia, Chacabuco y Pedernera, 5700, San Luis, Argentina. calopez@unsl.edu.ar.
authors.forename: C A
authors.identifier: http://orcid.org/0000-0002-5964-7103
authors.initials: CA
authors.lastname: López
authors.affiliation: INTEQUI, Universidad Nacional de San Luis, CONICET, Área de Química General e Inorgánica "Dr. G.F.Puelles"- Facultad de Química, Bioquímica y Farmacia, Chacabuco y Pedernera, 5700, San Luis, Argentina. calopez@unsl.edu.ar.
authors.forename: J C
authors.initials: JC
authors.lastname: Pedregosa
authors.affiliation: Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain.
authors.forename: J A
authors.identifier: http://orcid.org/0000-0001-5329-1225
authors.initials: JA
authors.lastname: Alonso