Nickel samarium oxide

Nickel samarium oxide (NiSmO₃), frequently referred to as samarium nickel oxide, is a synthetic mixed oxide with unusual thermo-optical properties. It and other nickel–rare earth oxides were prepared by Gérard Demazeau and co-workers at the University of Bordeaux (Talence, France) in 1971.

The crystalline oxides have typical ABX₃ perovskite structures (see image). Note that the nickel oxidation state is Ni(III).

In recent years, Mikhail A. Kats at the University of Wisconsin–Madison and colleagues there and at four other American research institutions discovered that NiSmO₃ appears to violate the venerable Stefan–Boltzmann law, which holds that the energy radiated from a black body is related to the body’s absolute temperature. Specifically, j* = σT⁴, where

• j* is the total energy radiated per unit surface area of the body per unit time,
• σ is the Stefan–Boltzmann constant, and
• T is the absolute temperature of the body.

Constant σ is related to two other derived physical constants and the speed of light in a vacuum.

The emitted energy is manifested as electromagnetic radiation. In practical terms, as an object is heated, the radiated light becomes brighter. With many substances, including NiSmO₃, the radiation is infrared light. But Kats and co-workers found that the IR radiation from NiSmO₃ does not brighten with increasing temperature.

Does NiSmO₃ really violate the Stefan–Boltzmann law? Not really. As Emily Conover, physics writer for Science News, put it,

[NiSmO₃] doesn’t flout the Stefan–Boltzmann law. Instead, the material’s increasing brightness at higher temperatures is counteracted by a decrease in its emissivity—the tendency to emit thermal radiation. That decrease occurs due to the material switching from an insulator to a metal. The two effects balance out so that, for certain infrared wavelengths, the material’s brightness remains constant as its temperature changes . . . .

According to Kats and colleagues, NiSmO₃ is the first known material to exhibit temperature-independent thermal radiation. They state that this phenomenon “has substantial implications for infrared camouflage, privacy shielding, and radiative heat transfer.”