title: Synthesis, Crystal Structure, and Properties of the Alluaudite-Type Vanadates Ag2-xNaxMn2Fe(VO4)3.
abstract: The new members of the Ag2-xNaxMn2Fe(VO4)3 (0 ≤ x ≤ 2) solid solution were synthesized by a solid-state reaction route, and their crystal structures were determined from single-crystal X-ray diffraction data. The physical properties were characterized by Mössbauer and electrochemical impedance spectroscopies, galvanostatic cycling, and cyclic voltammetry. These materials crystallize with a monoclinic symmetry (space group C2/c), and the structure is considered to be a new member of the AA'MM'2(XO4)3 alluaudite family. The A, A', M, and X sites are fully occupied by Ag(+)/Na(+), Ag(+)/Na(+), Mn(2+), and V(5+), respectively, whereas a Mn(2+)/Fe(3+) mixture is observed in the M' site. The Mössbauer spectra confirm that iron is trivalent. The impedance measurements indicate that the silver phase is a better conductor than the sodium phase. Furthermore, these phases exhibit ionic conductivities 2 orders of magnitude higher than those of the homologous phosphates. The electrochemical tests prove that Na2Mn2Fe(VO4)3 is active as positive and negative electrodes in sodium-ion batteries.
authors.affiliation: Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation , P.O. Box 5825, Doha, Qatar.|Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST) , 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
authors.forename: Hamdi
authors.initials: H
authors.lastname: Ben Yahia
authors.affiliation: Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST) , 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shikano
authors.affiliation: Research Institute of Electrochemical Energy, National Institute of Advanced Industrial Science and Technology (AIST) , 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan.
authors.forename: Mitsuharu
authors.initials: M
authors.lastname: Tabuchi
authors.affiliation: Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, Qatar Foundation , P.O. Box 5825, Doha, Qatar.
authors.forename: Ilias
authors.initials: I
authors.lastname: Belharouak