Order-disorder mixed phase in TlH2PO4

Abstract

An intermediate phase of partial order, associated with antiferroelectricity, is elucidated in hydrogen-bonded TlH2PO4 undergoing separated antiferroelectric and ferroelastic phase transitions. Our H-1 and P-31 nuclear magnetic resonance linewidth measurements revealed marked changes at an intermediate phase boundary, involving an intermediate phase of mixed order of coexistence of paraelectricity and antiferroelectricity, which was identified by means of impedance spectroscopy. A coupling of the proton and the PO4 tetrahedral motions to the proton ordering in the hydrogen bonds is also manifested.