Preparation and characterization of rubidium–β-alumina by the gel-to-crystallite conversion method

Abstract

Preparation of Rb–β-alumina was realized by the gel-to-crystallite conversion method. Reaction of hydrated aluminum hydroxide gel with RbOH in ethanol medium gave rise to the Rb +-inserted pseudoboehmite precursor under wet chemical conditions. The thermal decomposition of the precursor yielded Rb–β-alumina. The Rb 2O:Al 2O 3 ratio of monophasic Rb–β-alumina ranged from 1:10 to 1:22. The extended stability in the compositional range is due to the fact that the conduction planes containing Rb + and O 2− ions can have lower occupancy of Rb + ions for larger sized alkali ions, permitting the steric separation of the adjoining spinel blocks. High-resolution electron microscopy revealed that the decreasing occupancy of alkali ions in the conduction plane is balanced by changing widths of spinel blocks arising from the shift of tetrahedral Al 3+ ions to octahedral sites and an accompanying increase in stacking defects.