The variation in the formation energy of oxygen interstitials and O(1) oxygen vacancies as a function of temperature is shown in Fig. . For the La4Ni3O10, La2Pr2Ni3O10 and Pr4Ni3O10 structures, the temperature below which oxygen interstitials have lower formation energy than O(1) vacancies are predicted to be 723, 708 and 795 K, respectively at pO2 = 0.2 bar. This indicates that the defect chemistry of the LaxPr4-xNi3O10 structures can be subtly tuned via the x composition and that the thermal history of the sample and cooling conditions, such as the oxygen partial pressure and cooling rate may have a large impact.