Relaxor-like Dielectric Behavior in Stoichiometric Sillenite Bi12SiO20

A combination of fixed frequency dielectric measurements (10(3) to 10(6) Hz) and impedance spectroscopy reveal evidence of (nonferroelectric) relaxor-like behavior in the temperature range similar to 600-750 K for the stoichiometric sillenite phase Bi12SiO20 (space group I23, a = 10.1034(5) angstrom). Variable temperature Raman Spectroscopy reveals significant changes associated with the Bi-O framework vibrations, and the relaxor-type behavior is attributed to noncorrelated local dipole moments associated with the BiO5E (E = 6s(2) lone pair) units in the framework. Sillenites, therefore, represent another family of Bi-based oxides to exhibit relaxor-like dielectric behavior.