The neutron diffraction pattern obtained at 250˚C in flowing air for the L3P1N3 composition fitted best to an orthorhombic structure adopting the Bmab group. The lattice parameters were determined to be a = 5.42478(2) Å, b = 5.47534(2) Å and c = 27.9632(1) Å, and are in close agreement with the previously reported results for the end member materials . A phase transition was observed on further heating and the diffraction pattern collected at 800˚C was refined with tetragonal space group I4/mmm. The lattice parameters obtained after refinement again agree well with the literature for the end member composition and were a = b = 3.87876(1) Å, and c = 28.2287(2) Å . An impurity of ~2wt% NiO was also detected in the neutron diffraction data, which was not observed by X-ray diffraction measurements. The refinements of the data obtained at both temperatures, 250 and 800 ˚C, along with  2 and R factors are illustrated in Fig. . The transition to the tetragonal I4/mmm high symmetry structure at 800 ˚C in flowing air is clearly visible after scrutiny of the 2.3 to 2.6 Å d-spacing range (insets, Fig. and). A close inspection of the insets confirms the assignment of the two structural models (Bmab and I4/mmm) at low and high temperatures respectively. The lowsymmetry Bmab structure can be seen to show seven distinct reflections in the d-spacing range of 2.3-2.6 Å while the high-symmetry I4/mmm structure only shows three reflections in the same d-spacing range, thereby confirming the completion of the phase transition. The values of x, y, z and Uiso parameters determined by Rietveld refinement are provided in Table (250 ˚C) and S2 (800 ˚C) of the supporting information.