Terbium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties

Abstract

The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La1−xTbxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 °C, and 530 °C for La0.9Tb0.1NbO4+δ, La0.8Tb0.2NbO4+δ, and La0.7Tb0.3NbO4+δ, respectively. The impedance spectroscopy results suggest mixed conductivity of oxygen ions and electron holes in dry conditions and protons in wet. The water uptake has been analyzed by the means of thermogravimetry revealing a small mass increase in the order of 0.002% upon hydration, which is similar to the one achieved for undoped lanthanum orthoniobate.

Ceramic Conductors

“…Among them, electronic-, ionic-, as well as mixed electronic-ionic-conducting ceramics are very important groups of materials. Proton conductivity may be observed in acceptor-doped perovskite oxides such as Ba 0.9 La 0.1 Zr 0.25 Sn 0.25 In 0.5 O 3−a , as studied by Skubida et al [2], and terbium-substituted lanthanum orthoniobate [3]. Oxygen ions are mobile charge carriers in materials such as substituted bismuth vanadate [4] and doped cerium oxide [5,6], as studied by Ring and Fuierer, and to a minor extent and at high temperature, they are also mobile charge carriers in ceramic proton conductors.…”

“…The most often used method of ceramic materials preparation, which is usually used as a first-trial method, is the solid-state reaction method. This method was used for the preparation of doped barium indate Ba 0.9 La 0.1 Zr 0.25 Sn 0.25 In 0.5 O 3−a [2], terbium-doped lanthanum orthoniobate [3], and doped strontium titanate [8]. On the other hand, the solid-state reaction route often does not allow the achievement of single-phase ceramics with expected properties.…”

“…La-doped strontium titanate was studied as a ceramic component of a composite current collector in a metal-supported SOFC [8]. Similarly, the development of proton-conducting ceramics [2,3] is aimed at future applications in SOFCs with proton-conducting electrolytes. SOFCs both with oxygen ionand proton-conducting electrolytes operate at high temperatures, i.e., between 600 • C and 800 • C. Even the YF 3 -SrF 2 solid solutions are considered as electrolytes for high-temperature all-solid-state fluorine batteries [7].…”

Effects of Sn Doping and A‐Site Deficiency on the Phases and Electrical Conductivities of the High‐Temperature Proton Conductor LaNbO4

“…In addition, the effects of partial substitution of La 3þ for isovalent lanthanides, such as Ce, Pr, Nd, Sm, Gd, Yb, and Tb, on the thermal and electrical properties have also been reported. [20,29,31,33,35] Unfortunately, this also did not benefit the enhancement of the proton conductivity and resulted in an even lower conductivity than that of the single lanthanide La 3þ ions on the A-site.…”

High‐Temperature Proton Conduction in LaSbO4

“…The highest conductivity, 10 À3 Scm À1 at 800 8Ci nw et air,h as been achieved for Ca-dopedL aNbO 4 ; [14] however,t his conductivity level is much lowert han in the case of the proton-conducting perovskites. Consequently,m any attemptsh ave been made to increase the conductivity,m ostly by doping/substitution on both A- [23][24][25][26][27] and B-sites. [28,29] Despitea ll the efforts, it has not been possible yet to increase the conductivity to the desired level.…”