Lithium Manganese Nickel Oxides Lix ( MnyNi1 − y ) 2 − x O 2: I. Synthesis and Characterization of Thin Films and Bulk Phases

Abstract

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.