Effect of ytterbium oxide co-doping impurity on the structure and transport characteristics of (ZrO₂)_0.91-x(Sc₂O₃)_0.09(Yb₂O₃)_x (x = 0 - 0.02) single crystals

The use of solid electrolytes based on zirconia stabilizing scandium oxide results in a material with high ion conductivity. Electrolytic membranes made of such a material can significantly lower the operating temperature of an electrochemical device while maintaining high conductivity, which is very important for increasing the service life and reliability of electrochemical reactors, solid oxide fuel cells, electrolyzers and sensors.

The materials based on zirconia stabilized with scandium oxide phase boundaries are defined only approximate. This is due to the existence of metastable phases in this system and the dependence of the phase composition on the method and conditions of material synthesis. Additional doping of ZrO₂ ‑ Sc₂O₃ solid solutions with rare-earth oxides makes it possible to obtain stable cubic solid solutions with high conductivity.

The aim of this work is to assess the effect of the introduction of dopant ytterbium oxide into ZrO₂ – 9 mol.% Sc₂O₃ solid solutions in an amount from 0.5 to 2 mol.% on the phase composition, structure, and electrophysical properties of the material.

Single crystals of solid solutions were grown by directional crystallization of the melt in a cold container. The phase composition of the samples was controlled by Raman spectroscopy and X-ray diffractometry. The crystal structure was investigated by transmission electron microscopy. The study of the transport characteristics of crystals was carried out by the method of impedance spectroscopy in the temperature range 450 ‑ 900 C in the frequency range 1 Hz – 5 MHz.

It is shown that the stabilization of ZrO₂ together with 9 mol.% Sc₂O₃ and 1 mol.% Yb₂O₃ makes it possible to obtain transparent homogeneous crystals with a pseudocubic structure, which have high phase stability. The conductivity of the crystals depending on the concentration of Yb₂O₃ is nonmonotonic. The (ZrO₂)_0.9(Sc₂O₃)_0.09(Yb₂O₃)_0.01 crystals have a maximum conductivity in the investigated temperature range. An increase in the amount of Yb2O3 in the composition of the solid electrolyte to 2 mol% led to a decrease in the conductivity of the crystals due to the formation of oxygen-ion clusters. An increase in the concentration of ytterbium oxide to 2 mol% led to a decrease in the conductivity of the crystals due to the formation of oxygen-ion clusters.

The work was carried out under financial support of the Russian Science Foundation (grants № 19-72-10113)