Antimony substituted lanthanum orthoniobate proton conductor – Structure and electronic properties

Abstract

X‐ray and neutron diffraction have been utilized to analyze the crystalline and electronic structure of lanthanum orthoniobate substituted by antimony. Using X‐ray absorption spectroscopy and photoelectron spectroscopy, changes in the electronic structure of the material upon substitution have been analyzed. The structural transition temperature between fergusonite and scheelite phases for 30 mol% antimony substitution was found to be 15°C. Based on the neutron data, the oxygen nonstoichiometry was found to be relatively low. Moreover no influence on the position of the valence band maximum was observed. The influence of the protonation on the electronic structure of constituent oxides has been studied. Absorption data show that the incorporation of protonic defects into the lanthanum orthoniobate structure leads to changes in lanthanum electronic structure and a decrease in the density of unoccupied electronic states.

Vibrational Properties of LaNb0.8M0.2O4‐δ (M=As, Sb, V, and Ta)

“…The result of this study is presented in Figure 6(a). According to our previous studies, the structural transition temperature of LaNb 0.7 Sb 0.3 O 4 is in the range of 280 to 300 K [34] . As it is shown in Figure 6(b), with the lowering temperature, some changes in the region of 330 cm −1 can be seen.…”

“…The result of this study is presented in Figure 6(a). According to our previous studies, the structural transition temperature of LaNb 0.7 Sb 0.3 O 4 is in the range of 280 to 300 K. [34] As it is shown in Figure 6(b), with the lowering temperature, some changes in the region of 330 cm À 1 can be seen. Below approximately 260 K the relative intensity of two components of the split peak around 330 cm À changes which reflects the changes in the structure of the sample.…”

“…A similar relation is visible in changes in Raman modes between samples substituted by different elements. Moreover, the phase transition temperature of LaNb 0.7 Sb 0.3 O 4 has been established based on Raman spectroscopy measurement to be as low as 260 K which is lower than previously reported [34] …”

Solid oxide proton conductors beyond perovskites

“…However, the presence of this transition may be detrimental for practical electrolyte applications due to the different thermal expansion coefficients of the two phases (around 15 x 10 −6 °C-1 for the low temperature monoclinic phase and 8.6 x 10 −6 C -1 for the high temperature polymorph) and the tendency to microcracking 146 . The scheelite phase can be stabilised at room temperature via substitution of Nb with isovalent cations such as V, As, and Sb, generally resulting in an increase of the conductivity at lower temperatures 147,148,149,150 . Acceptor doping of LaNbO4 introduces extrinsic oxygen vacancies, enabling water absorption.…”

Praseodymium Orthoniobate and Praseodymium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

“…In the lanthanum sublattice, either acceptor dopants, i.e., Ca [ 17 ], Mg [ 18 ], Sr [ 19 ], Ba [ 20 ], or isovalent dopants, i.e., Ce (III) [ 21 ], Pr (III) [ 6 , 22 ], Nd and Sm [ 23 ], Tb (III) [ 7 ] and Yb [ 24 ], have been applied. In order to stabilize the structure and improve the conductivity, the substitutions in the niobium sublattice such as Al, Si, P, Ga, Ge and Bi [ 25 ], Ti [ 26 ], V [ 27 ], Cr, Mn, Sb [ 28 , 29 ] and Ta [ 27 ], Co [ 30 ], As [ 31 , 32 ], Zr [ 33 ], Mo [ 34 ], Sn [ 35 ] and W [ 36 ] have been tested.…”