Collective electron effects of O2− in potassium superoxide

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 Tc (193.5°K) reported by Carter and Templeton, the susceptibility is given by χ = c/(T + ϑ) with ϑ ∼ 250°K. Below Tc, 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 Tc. 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 Tc. 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.