ELECTRON NUCLEAR DOUBLE-RESONANCE NEAR FERROELECTRIC AND ANTIFERROELECTRIC PHASE-TRANSITIONS

A methodology is described for making electron nuclear double resonance (ENDOR) measurements on highly polar materials, such as the KH2PO4 -type of ferroelectrics (KH2PO4, KH2AsO4, RbH2AsO4, RbD2AsO4, CsH AsO and CsD2 AsO4) and the antiferroelectric NH4H2AsO4 in the vicinity of their phase transitions. Unlike EPR, the ENDOR lineshapes undergo drastic changes and yield direct information about the motional correlation time of a spin probe in the phase transition region. The ENDOR methodology enhances the spectral resolution and motional sensitivity of the EPR technique by approximately two orders of magnitude, and, thus, opens up another avenue for investigating molecular reorientations and, hence, the mechanism of ferroelectric transitions. © 1991, Taylor & Francis Group, LLC. All rights reserved.