Effect of cobalt deficiency on the structural phase transition in EuBaCo$_{2-x}$O$_{6-\delta}$

The effect of cobalt deficiency on the structural phase transition in the double layered cobaltite EuBaCo$_{2-x}$O$_{6-\delta}$ has been investigated using differential scanning calorimetry and high-temperature X-ray diffraction. It has been shown that, upon introduction of 5% cobalt vacancies, the energy and temperature of the phase transition from the orthorhombic unit cell (space group Pmmm) to the tetragonal unit cell (space group $P4/mmm$) decrease by 6% and 11$^\circ$C, respectively, as compared to the corresponding values typical of stoichiometric EuBaCo$_{2-x}$O$_{6-\delta}$. A model of the formation of cobalt–oxygen vacancies has been proposed.