Uniaxial relaxor ferroelectrics: The ferroic random-field Ising model materialized at last

Abstract

Owing to their intrinsic charge disorder ferroelectric crystals of strontiumbarium-niobate doped with Ce 3+ materialize the three-dimensional ferroic random-field Ising model (RFIM) as evidenced by order paramenter and susceptibility criticalities with 93 Nb NMR and dielectric spectroscopy, respectively. Upon cooling towards Tc, extreme critical slowingdown due to activated dynamic scaling gives rise to relaxor-like dispersion of the susceptibility and to a metastable ferroelectric nanodomain state with fractal size distribution as imaged by piezoelectric force microscopy.

Aging and slow dynamics inSrxBa1−xNb2O6

“…͑They are quite different from the prefactors of the critical dynamics near the higher-T peak in Ј, which have been found to be in the range of 10 7 Hz. 3 ͒ This freeze-out is evidently a purely kinetic phenomenon, i.e., a simple Arrhenius slowing down involving fixed barriers, rather than a thermodynamically cooperative effect in which barrier heights change. As such it is manifestly distinct from a lower-T cooperative phase transition found in some similar materials.…”

“…They could be larger than the domains if there are correlated realignments involving many domains. Typical domain size distributions in slowly cooled Ce-doped SBN, estimated from imaging techniques, 3 extend to around 3 ϫ 10 6 unit cells, if the unmeasured depths are comparable to the imaged dimensions. With obvious caveats involving comparisons of different materials, it seems likely that the coherent aging dynamics involve domain wall motions which usually involve a small domain or a fraction of a larger domain, rather than cooperative changes in many domains.…”

“…Most familiar relaxors are perovskites with cubic symmetry ͑at high temperature͒, but a few, such as Sr x Ba 1−x Nb 2 O 6 ͑SBN͒, are uniaxial. It has been proposed 3 that SBN may exemplify the random field Ising model ͑RFIM͒, 4 in contrast to cubic relaxors. In this paper we present a variety of measurements on SBN, including aging studies showing that the SBN relaxor regime is qualitatively distinct from the relaxor regime in several cubic materials.…”

Critical slowing down and elastic anomaly of uniaxial ferroelectricCa0.28Ba0.72Nb2O6crystals with tungsten bronze structure

“…For industrial demands, lead-free RFEs, such as SBN, have recently attracted much attention because of their outstanding functional properties under emerging environmental regulations. The ferroelectric phase transitions of the SBN family have been discussed within the random-field Ising model [3,4]. SBN shows excellent dielectric [5,6], piezoelectric [7], pyroelectric [8], and photorefractive properties [9][10][11][12].…”

Surface criticality in random field magnets

“…An intriguing possibility in this respect is the direct observation of the surface order parameter in relaxor ferroelectrics via piezoelectric force microscopy. 23 The excess exponents ␣ s and ␤ s , when inserted into the scaling relations ͑5͒ and ͑6͒, both yield very small values for the correction term ͑ − Ј͒, assuming ␣ Ϸ 0, ␤ Ϸ 0.02, and Ϸ 1.37. 13 This suggests that in fact Ј= , and the excess exponents are related to bulk exponents by the usual scaling laws valid for pure systems, Eq.…”