Oxygen transport and chemical compatibility with electrode materials in scheelite-type LaWxNb1−xO4+x/2 ceramic electrolyte

Exploring the nature of the fergusonite–scheelite phase transition and ionic conductivity enhancement by Mo6+doping in LaNbO4

“…19 Changes in total conductivity activation energies in scheelite-type phases are typically attributed to phase transitions or the onset of contributions from different charge carriers. 21 However, both LNMO16 and LNMO20 adopt the tetragonal scheelite structure over the whole temperature range represented by the data in Fig. 7, as their corresponding structural phase transition temperatures lie below the range covered by our impedance spectroscopy measurements.…”

“…One such doped system, LaNb 1Àx W x O 4+d (LNWO), has attracted recent interest due to its combination of low-toxicity elements, good redox stability and compatibility with candidate electrode materials such as NiO/YSZ (yttria-stabilised zirconia) and (La,Sr)MnO 3 . 21,22 The substitution of 8-16% W 6+ for Nb 5+ improves the total conductivity of LaNbO 4 by two orders of magnitude (to $10 À3 S cm À1 at 800 C) and also suppresses the signicant proton conductivity observed in undoped LaNbO 4 in humid atmospheres. 7,21 The fergusonitescheelite transition temperature is decreased by W 6+ doping, with the x ¼ 0.16 sample appearing almost tetragonal at room temperature.…”

“…21,22 The substitution of 8-16% W 6+ for Nb 5+ improves the total conductivity of LaNbO 4 by two orders of magnitude (to $10 À3 S cm À1 at 800 C) and also suppresses the signicant proton conductivity observed in undoped LaNbO 4 in humid atmospheres. 7,21 The fergusonitescheelite transition temperature is decreased by W 6+ doping, with the x ¼ 0.16 sample appearing almost tetragonal at room temperature. 23 The presence of interstitial oxide ions in LNWO also leads to modulated ordering schemes 24,25 similar to those observed in Ce 4+ -doped CeNbO 4+d .…”

Scheelite type Sr1−xBaxWO4 (x = 0.1, 0.2, 0.3) for possible application in Solid Oxide Fuel Cell electrolytes

“…Recently, alternative proton-conducting materials like acceptor-doped rare-earth materials, MTO 4 , where M = La, Ca, Sr, Ba, Y, Nd, Gd, Tb, Er, Pb, Cd and T = Nb, W, Mo, Mn have been suggested that offer high CO 2 tolerances based on the scheelite structure 31–36 . Proton conductivity dominates under wet conditions up to temperatures around 1,000 °C with a contribution of p-type electronic conduction, significant under oxidizing conditions above 800 °C.…”

“…Proton conductivity dominates under wet conditions up to temperatures around 1,000 °C with a contribution of p-type electronic conduction, significant under oxidizing conditions above 800 °C. LaNbO 4 -based materials exhibit moderate conductivity while being almost pure proton conductors, and for their stability in CO 2 -containing atmosphere and water vapour environment 31,37 . The highest proton conductivity recorded so far is the material LaNbO 4 when it contains minor A-site acceptor substitutions, such as Ca 0.01 La 0.99 NbO 4−d at 800 °C 38 .…”