Nickel Manganite Research Articles

Electrical conductivity and cation distribution in nickel manganite

A study has been made of the oxygen loss from nickel manganite at temperatures between 800 and 1220°C in atmospheres with oxygen partial pressures which varied from 0.12–100% oxygen using isothermal gravimetry. An atmosphere-temperature-composition diagram has been constructed which is used in conjunction with high temperature electrical conductance measurements to determine the concentration of conductance cations present in NiMn 2O 4. A comparison of results with those reported in the literature leads to a formula for the cation valence distribution in nickel manganite of Ni 2+ 0.35Mn 2+ 0.65 (Ni 2+ 0.65Mn 3+ 0.70Mn 4+ 0.65) O 2- 4 at 900°C. An equation for the variation of the nickel inversion parameter with temperature has also been derived.

X-ray photoelectron spectroscopy study of the cation valencies in nickel manganite

The X-ray photoelectron spectra of NiMn 2O 4, NiMnZnO 4, Mn 2TiO 4 MnFe 2O 4, and Mn 3O 4 are reported. The shift and broadening of the Mn-2 p, Mn-3 s, and Mn-3 p lines in NiMn 2O 4, compared with those of the other compounds, are indicative of the change distribution Ni 2+ 1−ν Mn 2+ ν[ Ni 2+ ν Mn 3+ 2(1−ν) Mn 4+ ν] O 4 (ν ⋍ 0.9) . The values of multiplet splitting of the Mn-3 s level also support this support this distribution.

Electrical Conductivity and Cation Valencies in Nickel Manganite

The change in the activation energy of the electrical properties of NiMn2O4 at about 400 °C and the sudden increase of the thermal expansion are indicative of the cation exchange between the octahedral and tetrahedral sublattices. During this exchange, the manganese ions have to change their valencies according to the reaction Mn + Mn + Ni → 2 Mn + Ni — 0.6 eV. This implies that the cation valencies in NiMn2O4 have to be represented with the formula NiMn(NiMnMn)O4.

Growth of nickel manganite single crystals

A method for growing single crystals of NiMn 2O 4 using Bi 2O 3-B 2O 3 as a flux is described. Chemical analysis indicated the presence of the phase NiMn 2O 4. The lattice constant, Curie temperature and magnetization agree well with values of polycrystalline material.

Preparation, semiconduction and low-temperature magnetization of the system Ni 1− xMn 12+ xO 4

The preparation of a complete range of solid solutions between the cubic spinel nickel manganite, NiMn 2O 4, and the tetragonal spinel, Mn 3O 4, is described. Studies of the crystal symmetry, the semiconductor behavior and low-temperature magnetization are reported each as a function of composition. Analysis of the crystal-chemical and thermoelectric properties leads to a tentative chemical formula for the system which provides an explanation for the electrical conductivity and magnetization. The conductivity involves the “hopping” of electrons from octahedral-site Mn 3+ ions to octahedral-site Mn 4+ ions. The unpredictable magnetic moments are also accounted for by the properties of octahedral-site Mn 3+ and Mn 4+ ions.

Infra-red absorption by copper and nickel manganites

Infra-red absorption by copper and nickel manganites