Lithium Manganese Nickel Oxides Li x ( Mn y Ni1 − y ) 2 − x O 2 : I. Synthesis and Characterization of Thin Films and Bulk Phases

The series for x ⩽ 1.33 and 0.38 ⩽ y ⩽ 0.50 shows a very close relationship to its parent series . The refined lattice parameters for at least 0.93 ⩽ x ⩽ 1.26 are a linear function of the concentration ratio Li/(Mn + Ni) which in turn is proportional to the averaged valence state of the transition metals. is able to reversibly coprecipitate/reinsert and release/absorb . This self‐regulation mechanism seems to always adjust the number of cations to an undisturbed oxygen sublattice according to the rule "cations/anions = 1," which holds true at least for temperatures up to 800°C and oxygen partial pressures above . Samples prepared in air and under did not show nucleation of , not even for x > 1.0. The series where 0.38 ⩽ y ⩽ 0.50 crystallizes in a rhombohedral unit cell (space group R3¯m ) for x < 1.15 and transforms into a single monoclinic phase (space group C2/c ) for x > 1.25. The similarity between and strongly suggests a rhombohedral → cubic transition at x ≈ 0.6 for the latter series. Derived from the linear dependence of the X‐ray density on the stoichiometric parameter x , an equation was found with which the lithium concentration of thin film phases over the entire range 0 ⩽ x ⩽ 1.33 can be determined accurately without extensive ion‐beam analysis. XPS measurements on a film with the bulk stoichiometry gave evidence for and but no indication was found for nickel valence states other than . In order to meet the above‐given stoichiometry, the averaged nickel valence state had to increase with film depth.