No P3-type phase of NaxMO2 with x close to unity

Layered AxMO2 phases attract great attention as electrode materials for high-energy density batteries. The main structural variants in this family are know n as O3, P2 and P3. Previous experimental data and theoretical considerations have shown that prismatic structures with A = Na or K can only be stable at x values significantly lower than unity, typically 0.6–0.8 for P2 and 0.5–06 for P3 (if any). This was challenged by recent reports on P3-type Na0.9(Fe0.5Mn0.5)O2 and Na(Cu0.2Fe0.1Mn0.7)O2. We found, however, that the reported XRD patterns strongly disagree with the reported structures and compositions. For the former, actual lattice parameters correspond to an x value much lower than 0.9, and the latter is actually P2 type with x close to 0.74. The XRD pattern disagree with the reported unit cell parameters.Vertical bars are calculated Bragg positions not shown in the original paper. [Display omitted] •It is explained why prismatic AxMO2 structures do not appear at x close to 1.•Two published XRD patterns strongly disagree with the reported lattice parameters.•Refined lattice parameters of “Na0.9(Fe0.5Mn0.5)O2“indicate much lower Na content.•“P3–NaCu0.2Fe0.1Mn0.7O2“ is actually P2-NaxCu0.2Fe0.1Mn0.7O2 with x ≈ 0.74•All of this is a caveat for journal reviewers!.