Collective electron effects of O₂⁻ in potassium superoxide Available to Purchase

A temperature variation study of dc conductivity, magnetic susceptibility, and ESR on powdered potassium superoxide has been carried out. Also reported is a room temperature measurement of the electronic absorption spectrum. We find that at temperatures above the structural phase transition temperature T_c (193.5°K) reported by Carter and Templeton, the susceptibility is given by χ = c/(T + ϑ) with ϑ ∼ 250°K. Below T_c, χ = c′/(T + ϑ) with ϑ′ ∼ 18°K. There is no magnetic ordering down to liquid nitrogen temperature. ESR spectra shows two distinct lines above T_c. The broad line is Lorenzian in shape with a width at half‐maximum of about 700 G. The narrow line has a width of 25 G and the area under this resonance is 10⁻⁴ times that under the broad one. The broad line splits into two below T_c. The number of spins contributing to the broad resonance has a temperature dependence which is qualitatively similar to that of the susceptibility. The narrow ESR line persists through the phase transition. At temperatures greater than 250°K, KO₂ is semiconducting with an activation energy of 1.3 eV. The yellow color of KO₂ at room temperature is due to an absorption band peaked at 350 nm degrading to 600 nm. A simple theoretical model based on correlation and disorder is proposed which can explain most of these experimental data.