Several million kilograms are produced annually of varying quality, mainly as an intermediate in the production of nickel alloys.

[6] The simplest and most successful method of preparation is through pyrolysis of nickel(II) compounds such as the hydroxide, nitrate, and carbonate, which yield a light green powder.

[4] Synthesis from the elements by heating the metal in oxygen can yield grey to black powders which indicates nonstoichiometry.

Charles Édouard Guillaume won the 1920 Nobel Prize in Physics for his work on nickel steel alloys which he called invar and elinvar.

[5] Black NiO is the precursor to nickel salts, which arise by treatment with mineral acids.

[8][citation needed] For instance, the seemingly simple material NiO has a partially filled 3d-band (the Ni atom has 8 of 10 possible 3d-electrons) and therefore would be expected to be a good conductor.

However, strong Coulomb repulsion (a correlation effect) between d-electrons makes NiO instead a wide band gap Mott insulator.

[13][12] Nickel oxide is classified as a human carcinogen[14][15][16][17][18][19] based on increased respiratory cancer risks observed in epidemiological studies of sulfidic ore refinery workers.