Investigation of the Electronic and Structural Properties of Potassium Hexaboride, KB6, by Transport, Magnetic Susceptibility, EPR, and NMR Measurements, Temperature-Dependent Crystal Structure Determination, and Electronic Band Structure Calculations

The electronic and structural properties of potassium hexaboride, KB6, were examined by transport, magnetic susceptibility, EPR, and NMR measurements, temperature-dependent crystal structure determination, and electronic band structure calculations. The valence bands of KB6 are partially empty, but the electrical resistivity of KB6 reveals that it is not a normal metal. The magnetic susceptibility as well as EPR and NMR measurements show the presence of localized electrons in KB6. The EPR spectra of KB6 have two peaks, a broad (∼320 G) and a narrow (less than ∼27 G) line width, and the temperature-dependence of the magnetic susceptibility of KB6 exhibits a strong hysteresis below 70 K. The temperature-dependent crystal structure determination of KB6 shows the occurrence of an unusual variation in the unit cell parameter hence supporting that the hysteresis of the magnetic susceptibility is a bulk phenomenon. The line width ΔH pp of the broad EPR signal is independent of temperature and EPR frequency. This finding indicates that the line broadening results from the dipole−dipole interaction, and the spins responsible for the broad EPR peak has the average distance of ∼1.0 nm. To explain these apparently puzzling properties, we examined a probable mechanism of electron localization in KB6 and its implications.