abstract
Undoped LnVO(4) and magnesium-doped Ln(0.95)V(0.95)Mg(0.10)O(4.8) (Ln = Pr, Sm, Gd, Dy and Er) orthovanadates were synthesized by solid state reaction method and characterized by XRD, SEM/EDS, electrical conductivity measurements in controlled atmospheres, and modified e.m.f. technique for determination of oxygen-ion transference numbers. XRD analysis showed the formation of phase-pure materials with tetragonal zircon-type structure and a decrease in lattice parameters with a decrease of ionic radius of rare-earth cations. Trace amounts of MgO and Mg-V-0 phases revealed by SEM/EDS suggest that the solid solubility limit of magnesium cations in LnVO(4) lattice is somewhat lower than the nominal doping level, and that magnesium substitutes preferentially into the vanadium sublattice. LnVO(4) and Ln(0.95)V(0.95)Mg(0.10)O(4.8) orthovanadates show semiconducting behavior under oxidizing conditions at 450-950 degrees C and are predominantly oxygen-ionic conductors, except PrVO4 that shows mixed conductivity. In the LnVO(4) series, electrical conductivity is the highest for PrVO4 and SmVO4 (similar to 4 x 10(-4) S/cm at 800 C) and decreases with increasing atomic number of rare-earth cation for the other compositions. Additions of magnesium results in a drop of electrical conductivity, by 1.5-2 times for most of compositions. Interstitial oxygen diffusion is discussed as a prevailing mechanism of ionic transport in undoped LnVO(4), whilst acceptor-type magnesium doping suppresses the formation of interstitial oxygen ions. Humidity has a rather negligible impact on the electrical properties of substituted ceramics, indicating only minor (if any) protonic contribution to the total electrical transport of the studied orthovanadates.
keywords
TRANSPORT-PROPERTIES; ANODE MATERIALS; OXIDE; CONDUCTIVITY; TRANSITION; STABILITY; DEFECTS; CA; CEVO4; GD
subject category
Materials Science
authors
Gayathri, TH; Yaremchenko, AA; Macias, J; Abhilash, P; Ananthakumar, S
our authors
Aleksey Yaremchenko
Principal Researcher
Javier Macias Montiel
PhD StudentProjects
acknowledgements
T.H.G. and P.A. thank the Council of Scientific and Industrial Research for the research fellowship. The authors thank Dr. K.P. Surendran (CSIR-NIIST) and Dr. D.P. Fagg (TEMA-NRD, University of Aveiro) for their help. A.Y. and J.M. would like to acknowledge financial support from the FCT, Portugal (project IF/01072/2013/CP1162/CT0001 and project CICECO-Aveiro Institute of Materials POCI-01-0145-FEDER-007679 (FCT ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement).