Defect rocksalt structures in the La-Na-N system

Raw powder X-ray diffraction datasets for the profiles shown in Fig. 1 of the publication Yao Yuan, Simon D. Kloß, and J. Paul Attfield (in submission). "Defect rocksalt structures in the La-Na-N system." Philosophical Transactions A., 10.1098/rsta.2022.0329 . Sodium azide (NaN3) is a versatile nitrogen source that can be used for the synthesis of new nitrides under high pressure and temperature conditions. Reactions between lanthanum nitride (LaN) and sodium azide (NaN3) at 800 °C under 8 GPa pressure have led to the discovery of two defect rocksalt phases which are the first reported ternaries in the La-Na-N system. Preliminary structure assignments have been made based on fits to powder X-ray diffraction profiles. One phase is La1-xNa3xN with vacancies at octahedral La sites and interstitial tetrahedral Na cations. This phase has a tetragonally distorted rocksalt structure (space group I4/mmm, a = 3.8704(2) and c = 5.2098(3) Å for nominal x = 0.10) and the distortion decreases with increasing Na content (space group I4/mmm, a = 3.8060(2) Å, c = 5.2470(3) Å for nominal x = 0.14), further giving a cubic Fm3̅m phase (a = 5.3055(2) Å) for nominal x = 0.25. This coexists with another cubic Fm3̅m phase (a = 5.1561 (5) Å), tentatively identified as rocksalt ‘NaN1/3’ stabilised by a small amount of La; NaLayN(1+3y)/3 with y ≈ 1%. These initial investigations reveal that the high pressure La-Na-N phase diagram may be rich in defect rocksalt type materials although further work using neutron diffraction will be needed to confirm the structures.