Seebeck coefficient and electrical conductivity are measured at 1300 K vs. oxygen partial pressure in the range between . Comparative analysis of both parameters indicates that the mobility term for electron holes in undoped is changing vs. oxide composition. Its average value is: . Singly ionized cation vacancies were established as predominant defects for undoped and doubly ionized cation vacancies for solid solutions. No simple relationship is observed between the concentration of Cr incorporated into and the generated hole concentration as predicted by the controlled valency theory. In contrast to this theory, the experimental data indicate a strong decrease of the Fermi energy vs. Cr concentration for solid solutions. Accordingly, significant interaction between point defects in Cr‐doped crystal is postulated. The application of the Debye‐Huckel theory for strong electrolytes allows for the calculation of which is in an agreement with experimental results. The defect equilibrium constants are calculated for formation of singly and doubly ionized cation vacancies in at 1300 K and