Random fields in dipolar glasses and relaxors

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-x Li x TaO 3 (x < 0.02), quenched random-fields (RFs) due to charge disorder dominate the uniaxial relaxor Sr 1-x Ba x Nb 2 O 6 (SBN, x 0.4). RFs smear the glass transition of Rb 1-x (DH 4 ), 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 O 3 (PMN) rather obey spherical RBRF modeling. In the case of relaxors spatial fluctuations of the RFs correlate the dipolar fluctuations 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).