Ga-substitution effects on the improper ferroelectric phase transition of Ca8[AlO2]12(MoO4)2

Abstract

The aluminum-sodalite-type oxide, Ca8[AlO2]12(MoO4)2, shows an improper ferroelectricity below a ferroelectric phase transition temperature around 630 ​K. Here we present effects of a Ga-substitution for Al on ferroelectric properties of Ca8[AlO2]12(MoO4)2. Systematic investigations with synchrotron x-ray powder diffractions and dielectric/pyroelectric measurements have clarified that the Ga-substitution suppresses the ferroelectricity and markedly enhances a thermal hysteresis of the ferroelectric phase transition. In contrast to the case of Sr-substitution for Ca, with which the ground state results in a relaxor-like state, the polar ordering of macroscopic scale has been found to survive under the Ga-substitution. The present results shed light on intuitive designing of ferroelectricity and the phase transition properties in the aluminum-sodalite-type oxide.

Keywords

• Improper ferroelectricity
• Structural phase transitions
• Sodalites