Phase Behavior and Defect Structure of HoBaCo[sub.2]O[sub.6-δ]

The differential scanning calorimetry study showed that the double perovskite HoBaCo[sub.2] O[sub.6-δ] (HBC), depending on its oxygen content, undergoes three phase transitions in the temperature range 298–773 K. Their origin was tentatively explained using the relevant literature data. For the single-phase tetragonal HBC, the oxygen nonstoichiometry dependences on the oxygen partial pressure were investigated by thermogravimetric and flow reactor methods in the intermediate-temperature range of 573–773 K. The proposed defect structure of HBC was successfully verified using the obtained data on its oxygen nonstoichiometry combined with those reported earlier. As a result, the values of the thermodynamic parameters (∆H[sub.i] [sup.∘] , ∆S[sub.i] [sup.∘] ) of the defect reactions proceeding in HBC were determined. The defect structure of HBC was shown to be similar to that of YBaCo[sub.2] O[sub.6-δ] (YBC) likely due to similar ionic radii of Ho[sup.3+] and Y[sup.3+] .