Insulating phase of potassium clusters arrayed in low-silica-type zeolite FAU

Mutually interacting potassium clusters stabilized in supercages of aluminosilicate zeolite FAU (Si/Al = 1). the so-called low-silica X, are investigated in terms of optical and magnetic properties. FAU is ion-exchanged to K, and denoted by K-FAU(1), hereafter. When metal K is adsorbed at the average loading density of 0.7 +/- 0.3 atom per supercage of FAU, the observed infrared absorption is more than one order weaker than that in similarly K-loaded samples of K-FAU(1.25) which is called X commonly. The Weiss temperature in K-loaded K-FAU(1) is - 33 +/- 3 K. This value is several times larger than that in K-loaded K-FAU(1.25). The Mott insulator phase in K clusters in FAU(1), is thought to be realized differently from the metallic phase of K-FAU(1.25). (C) 2001 Elsevier Science B.V. All rights reserved.