Missing valence states, diamagnetic insulators and superconductors.
01 January 1988
About fifteen elements in the periodic table skip certain valences in all the compounds they form. This is understood to arise from a negative effective intra-atomic interaction. A model with such interactions as well as inter-atomic repulsions gives insulating behavior near half-filling and superconductivity farther from it in agreement with the properties of BaPb sub x Bi sub (1-x) O sub 3 and Ba sub x K sub (1-x) BiO sub 3.