To aid the neutron diffraction results, DFT calculations were used to investigate the formation energy of oxygen vacancies and oxygen interstitials. The energy to form an oxygen vacancy at each of the 5 distinct O sites (O1 -O5) in the lowest energy La2Pr2Ni3O10 and end member La4Ni3O10 and Pr4Ni3O10 structures was calculated as shown in Fig. .