Random-field models for relaxor ferroelectric behavior

Abstract

Heat bath Monte Carlo simulations have been used to study a four-state clock model with a type of random field on simple cubic lattices. The model has the standard nonrandom two-spin exchange term with coupling energy J and a random field which consists of adding an energy D to one of the four spin states, chosen randomly at each site. This Ashkin-Teller-like model does not separate; the two random-field Ising model components are coupled. When D/J = 3, the ground states of the model remain fully aligned. When D/J ≥ 4, a different type of ground state is found, in which the occupation of two of the four spin states is close to 50%, and the other two are nearly absent. This means that one of the Ising components is almost completely ordered, while the other one has only short-range correlations. A large peak in the structure factor S(k) appears at small k for temperatures well above the transition to long-range order, and the appearance of this peak is associated with slow, "glassy" dynamics. The phase transition into the state where one Ising component is long-range ordered appears to be first order, but the latent heat is very small.

Neutron and x-ray diffraction study of cubic [111] field-cooledPb(Mg1∕3Nb2∕3)Stock1, Xu2, Gehring3 et al. 2007Phys. Rev. B603462View full textAdd to dashboardCite

“…8 Dielectric measurements have found the presence of a frozen glassy state at low temperatures and have led to theories of random bond and field effects in analogy to the case of spin glasses. [9][10][11][12] Recent neutron and x-ray scattering studies conducted on PMN and PZN in zero field have found no long-range structural distortion in the bulk at low temperatures. This new phase ͑referred to as phase X in the original measurements͒ was first measured and presented based on neutron diffraction measurements on PZN doped with 8% PT.…”

Competing Orders in PZN–xPT and PMN–xPT Relaxor Ferroelectrics

“…The frustration between charge neutrality and lattice strain which does not favor a 1 : 2 order makes it unlikely for any long-range cation/chemical order to form in these relaxor systems. The charge imbalance due to the randomness of B-site occupancy creates local random fields, which is the key in understanding many relaxor properties 5,6,7,8,9 .…”

Ferroelectricity in Silver Perovskite Oxides

“…PE and FE denote paraelectric and ferroelectric states, respectively. The gray zone may be a dipolar-glass state (Pirc & Blinc, 1999) or a state with nanosized ferroelectric domains (Fisch, 2003;Fu et al, 2009b).…”

“…On the basis of the above results, a phase diagram is proposed in Fig.31, in which PE and FE represents the paraelectric and ferroelectric phases, respectively. As mentioned above, since the peak of the dielectric constant is strongly dependent with frequency for 0<x<0.035, the gray zone in the phase diagram may be attributed to dipole-glass phase (Vugmeister & Glinchuk, 1990;Pirc & Blinc, 1999;Samara, 2003) or a phase with nanosized ferroelectric domains (Fisch, 2003;Fu et al, 2009b), which remains to be addressed by further investigations.…”