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

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, Nd_1.8Gd_0.2Zr₂O₇, Nd_1.8Gd_0.1Yb_0.1Zr₂O₇, Nd_1.4Gd_0.6Zr₂O₇ and Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ 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 Nd_1.4Gd_0.3Yb_0.3Zr₂O₇ ceramic.