Improvement of Electrical Conductivity of Trivalent Rare‐earth Cation‐doped Neodymium Zirconate by Co‐doping Gadolinium and Ytterbium

Abstract

Pyrochlore oxides of A2Zr2O7, where A represents trivalent rare‐earth elements, have a high electrical conductivity, which makes them suitable for applications as high‐temperature solid electrolytes. The influence of Gd and Yb cations co‐doping at the Nd site on structure and electrical conductivity of a pyrochlore oxide Nd2Zr2O7 is investigated using X‐ray diffraction and impedance spectra measurements. Different zirconate ceramics of Nd2Zr2O7, Nd1.8Gd0.2Zr2O7, Nd1.8Gd0.1Yb0.1Zr2O7, Nd1.4Gd0.6Zr2O7 and Nd1.4Gd0.3Yb0.3Zr2O7 are prepared by pressureless‐sintering method at 1,973 K for 10 h in air. Nd2Zr2O7 doped with Gd and Yb cations at the Nd site exhibit a single phase of pyrochlore‐type structure. The measured values of the total conductivity obey the Arrhenius relation. Nd2Zr2O7 and its doped zirconate ceramics are oxide‐ion conductors in the oxygen partial pressure range of 1.0 × 10–4 to 1.0 atm at all test temperature levels. The total conductivity increases with reducing average ionic radii of A‐site rare‐earth cations. The dual Yb+Gd intermix doping causes a distinctly enhanced total conductivity as compared to unmodified Nd2Zr2O7 and singly Gd‐doped zirconate ceramics. The highest total conductivity value obtained in this work is 1.02 × 10–2 S cm × 1 at 1,173 K for Nd1.4Gd0.3Yb0.3Zr2O7 ceramic.

Induced oxygen vacancies and their effect on the structural and electrical properties of a fluorite-type CaZrO3–Gd2Zr2O7 system

“…3 The intercepts of the arcs with the real axis would yield the value of resistance, R, from which the conductivity of the materials can be calculated using the relation,…”

Relationship between crystal structure and oxide-ion conduction in <i>Ln</i>₂Zr₂O₇ (<i>Ln</i> = Eu, Nd and La) system deduced by neutron and X-ray diffraction

“…6)11),13), 14) Yamamura et al 6) have reported the oxide-ion conductivity of the fluorite or pyrochlore phases in the Ln 2 Zr 2 O 7 and (Ln 1¹x LnB x ) 2 -Zr 2 O 7 (Ln, LnB = La, Nd, Gd, Eu, Sm, Y and Yb) systems. They concluded that the oxide-ion conductivity increased with increasing ionic radius ratio in the fluorite phase range, showed the sharp maximum (Eu 2 Zr 2 O 7 showed the highest conductivity of 8.3 © 10 ¹3 S/cm at 1073 K) in the vicinity of the phase boundary in the pyrochlore phase range, and then decreased.…”

Electrical Conductivity Improvement of Nd2Ce2O7 Ceramic Co‐doped with Gd2O3 and ZrO2

“…In the ideal case, the frequency dependent complex admittance of polycrystalline electrolytes can be modelled by a resistor-capacitor (RC) pair in parallel. However, in the present case, in place of capacitor a constant phase element (CPE) is required to model the experimental data [20], as shown in Figure 2( 7 , respectively, which correspond to the grain contributions. The impedance spectra of (Nd 1-x Gd x ) 2 (Ce 1-x Zr x ) 2 O 7 ceramics show only a single semicircle, suggesting that the contribution from the resistance of grain boundary was negligibly small.…”

“…These properties make A 2 B 2 O 7 -type oxides suitable for extensive applications such as hightemperature thermal barrier coating materials, catalysts and solid electrolytes, etc. [2][3][4][5][6][7]. The intrinsic anion vacancy enables A 2 B 2 O 7 -type oxides possess high electrical conductivity, and can be considered as a potential candidate for solid electrolytes.…”