After heating, the sample is mainly composed of an orthorhombic phase (see section 3.1), which we assign the label orthorhombic #1 in the following discussion. Orthorhombic distortions within RP-type material can have different origins: pure La2NiO4 is known to crystallize in the orthorhombic space group Pmnb, where the distortion originates from tilting of the octahedra within the a/b-plane, which mainly changes the coordination around the Laions. In addition, orthorhombic distortions can also occur when filling of the interstitial sites take place, e.g., as observed for La2NiO3F2 with space group Cccm, in which case the orthorhombic distortion is caused by the additional space required by the fluoride ions within the interlayers and accompanied by a moderate increase of the lattice parameter c (see Figure ). Both, tilting occurring on increased ordering of anions as well as small degrees of anion exchange reactions according to the following reaction equation and cannot be assigned clearly: