Phase transition in alkali-electro-sodalite studied by ESR

AES (A= Na, K) is a Mott insulator at room temperature consisting of a bcc sub-lattice of F-centers, supported by a zeolite-like framework. Each sodal ite cage contains an s-like electron trapped by a spherical potential due t o four tetrahedrally arranged alkali cations. On cooling, SES and KES under go an AF transition at about 50 and 70 K respectively, providing the first example of an s-electron antiferromagnet. ESR linewidth, lineshape and g-sh ift were measured, which shows unique feature of these s-electron lattices. The linewidth is narrow above T-N due to exchange narrowing and rapidly br oadens below T-N. Under high pressures AES could be metal.