Crystal structure and ionic conductivity of novel rare-earth niobates LnNbO4 (Ln = Nd, Sm, Eu, Gd) by substituting Nb with W

Variable Temperature In Situ Neutron Powder Diffraction and Conductivity Studies of Undoped HoNbO4 and HoTaO4

“…The increase of the activation energy ( E act. ) above the phase transition is contrary to the literature results for pure and A-site-doped LaNbO 4 , suggesting that the size of the A-site cation may play a role as Ho 3+ is smaller than La 3+ . ,, A corresponding change in the slope was not observed for HoTaO 4 materials as the phase transition occurs at a much higher temperature than the measured ionic conductivity range (Figure ). Although measuring the conductivity across the P 2/ c – I 4 1 / a phase transition of HoTaO 4 would be interesting, the experimental procedure is extremely challenging. , In addition, the phase transition temperature of 1300 °C is outside the moderate SOFC operating temperature of 500–750 °C.…”

Investigation of the crystal structure and electrochemical performance of Gd doped LaNb0.9Mo0.1O4.05

“…Also, the large amount of substitution at the Nb sites could form clusters, which could trap the oxygen interstitials. 22 Another reason could be related to the different microstructure of the samples, although this cannot be confirmed as prior work did not include this information. The conductivity of LNM10 is also higher than the work reported by Li et al , (3.00 × 10 −3 S cm −1 for LaNb 0.92 W 0.08 O 4.04 measured at 800 °C in air) and Canu et al (1.40 × 10 −3 S cm −1 for LaNb 0.84 W 0.16 O 4.08 measured at 800 °C in air).…”

“…16,18 Ryo et al , also used W as the dopant on the Nb sites of GdNbO 4 ; the results showed that the conductivity of GdNbO 4 was improved by the substitution of W and there was no modulated structure found in this type of material. 21,22 The absence of a modulated structure was also found in other W-doped lanthanide (Pr, Nd) ortho -niobates, where Pr and Nd both have smaller ionic radii compared with La. 11,16 Therefore, the existence of the modulated structure could be related to the cell volumes.…”