Random Fields at Transitions from Relaxor to Glassy and Ferroelectric States

Abstract

In dipolar glasses and relaxors both site and substitutional charge disorder generally occur simultaneously albeit with different weight. While random interactions control dipolar glassy behavior of K 1 m x Li x TaO 3 ( x < 0.02), quenched random-fields ( RF s) due to charge disorder dominate the uniaxial relaxor Sr 1 m x Ba x Nb 2 O 6 (SBN, x , 0.4). RF s smear the glass transition of Rb 1 m x (DH 4 ) x H 2 PO 4 (DRADP, x , 0.5) as described by a random-bond random-field ( RBRF ) Ising model, while cubic relaxor glasses like PbMg 1/3 Nb 2/3 O 3 (PMN) obey spherical RBRF modeling. Spatial fluctuations of the RF s correlate the dipolar fluctuations of relaxors and give rise to polar nanoregions in the paraelectric regime. The order parameter dimension decides upon whether the ferroelectric phase transition is destroyed (PMN) or modified towards random-field Ising model behavior (SBN).