ESR- and magnetic susceptibility measurements on the potassium molybdenum bronzes

Magnetic and transport properties of the transition metal bronzes are determined by the extent of delocalization of the transition metal 4d-electrons. We report on ESR investigations of single crystals of the “red” potassium molybdenum bronze K_0.33MoO₃ and of the “blue” potassium molybdenum bronze K_0.30MoO₃. ESR spectra due to unpairedd-electrons are observed at both compounds. Analyzing the hyperfine structure we find that thed ¹-electrons are delocalized over six molybdenum lattice sites in semiconducting K_0.33MoO₃. The same K_0.33MoO₃ crystals show another spectrum which is caused by pairs of exchange coupledd-electrons. Our results are compared with those from magnetic susceptibility measurements and are discussed in connection with the crystal structure of K_0.33MoO₃ and K_0.30MoO₃.