Equilibrium of intrinsic and impurity point defects in Ca-doped Sm$_2$Zr$_2$O$_7$

In this work, a doping strategy was used to achieve a good conductivity in samarium zirconate which crystallizes in the pyrochlore. The production of nanopowders made it possible to form high-density ceramics with an optimal microstructure. It is shown that intrinsic and impurity defects coexist in Sm$_{2-x}$Ca$_x$Zr$_2$O$_{7-\delta}$, impairing ion transport at high doping levels. Despite this, Sm$_{1.95}$Ca$_{0.05}$Zr$_2$O$_{7-\delta}$ maintains low activation energy of the parent and has good ionic conductivity (10$^{-3}$ S $\cdot$ cm$^{-1}$ at 600$^\circ$C) which is one of the largest among oxide pyrochlores. It has been shown to have a good chemical stability. The material has a thermal expansion coefficient (TEC) of 12 ppm K$^{-1}$ which is higher than YSZ and provides better compatibility with electrode materials. The above makes it possible to successfully use it as a highly stable oxygen electrolyte or an intermediate thin layer at the electrolyte-electrode interface in electrochemical devices.