Magnetism of F centers; indication of an antiferromagnetic phase transition in potassium-electro-sodalite

Abstract

Temperature-dependent EPR data of potassium-electro-sodalite (PES), K8[Al6Si6O24](e-) 2, are consistent with the occurrence of an antiferromagnetic phase transition at 71±2 K. PES is a Mott insulator which contains an unpaired electron in every sodalite cage. The same transition in sodium-electro-sodalite occurs at a considerably lower temperature (42 K), indicating that the exchange interaction among localized elections is stronger in PES. PES is obtained by the inclusion of one potassium atom in every cage of potassium sodalite. The 27Al MAS NMR resonance of PES is shifted downfield in respect to diamagnetic potassium-sodalite, K6[Al6Si6O24]. The NMR shift is due to unpaired electrons and is caused by hyperfine Fermi contact interaction.