Landau, Ginzburg, Devonshire and others

Macroscopic modelling of ferroelectric properties refers usually to Landau-Ginzburg-Devonshire theory. This paper questions the meaningfulness of this term, discussing contributions of the three authors to what is supposed to be a theory. The limitations of every contribution are analyzed. In the main text and, to more extent in the Supplementary Material, the Landau theory is presented from an unusual perspective starting from simple mechanical models of spontaneous symmetry breaking and finishing by the Ising model. The aim of the presentation is to emphasize along with the qualitative breakthroughs the approximate character of macroscopic modelling associated with the above three authors.Comment: 37 pages, 16 figures, submitted to Ferroelectric

Influence of long-range dipolar interactions on the phase stability and hysteresis shapes of ferroelectric and antiferroelectric multilayers

Phase transition and field driven hysteresis evolution of a two-dimensional Ising grid consisting of ferroelectric-antiferroelectric multilayers that take into account the long range dipolar interactions were simulated by a Monte-Carlo method. Simulations were carried out for a 1+1 bilayer and a 5+5 superlattice. Phase stabilities of components comprising the structures with an electrostatic-like coupling term were also studied. An electrostatic-like coupling, in the absence of an applied field, can drive the ferroelectric layers towards 180º domains with very flat domain interfaces mainly due to the competition between this term and the dipole-dipole interaction. The antiferroelectric layers do not undergo an antiferroelectric-to-ferroelectric transition under the influence of an electrostatic-like coupling between layers as the ferroelectric layer splits into periodic domains at the expense of the domain wall energy. The long-range interactions become significant near the interfaces. For high periodicity structures with several interfaces, the interlayer long-range interactions substantially impact the configuration of the ferroelectric layers while the antiferroelectric layers remain quite stable unless these layers are near the Neel temperature. In systems investigated with several interfaces, the hysteresis loops do not exhibit a clear presence of antiferroelectricity that could be expected in the presence of anti-parallel dipoles, i. e., the switching takes place abruptly. Some recent experimental observations in ferroelectric-antiferroelectric multilayers are discussed where we conclude that the different electrical properties of bilayers and superlattices are not only due to strain effects alone but also long-range interactions. The latter manifests itself particularly in superlattices where layers are periodically exposed to each other at the interfaces

Check the weather before you hang the laundry! Accounting Turkish progress in anti-money laundering mechanisms

This paper examines the anti-money laundering (AML) legislation in Turkey and the European Union (EU). Given the fact that Turkey is officially a candidate country for the EU membership, harmonisation of Turkish and the EU AML frameworks has become increasingly important. These AML laws pose important responsibilities for the financial sector. Accordingly, the role of accountants both at global and regional level against money laundering has a great significance. We compare and evaluate specific AML provisions pertaining to obligations of Turkish accountants with those in the EU. In order to facilitate the evaluation process, the AML regimes examined are compared in regards to various aspects such as criminalization of money laundering, recording and reporting obligations for accountants, enforcement and sanctions mechanisms. While we have found that each national regime has adopted a unique AML framework, minimum standards provided by international (e.g. the Financial Action Task Force) and regional (e.g. EU) instruments have been the main driving force behind all national laws. While we have made some feasible recommendations for reform, based on our analysis, we have concluded that a comprehensive evaluation of the success of the Turkish AML regime is difficult to determine as there are no cases studies (e.g. prosecutions, convictions, etc.) and this will require further research

Potential barrier increase due to Gd doping of BiFeO3 layers in Nb:SrTiO3-BiFeO3-Pt structures displaying diode-like behavior

The rectifying properties of Nb:SrTiO3-Bi1-xGdxFeO3-Pt structures (x = 0, 0.05, 0.1) displaying diode-like behavior were investigated via current-voltage characteristics at different temperatures. The potential barrier was estimated for negative polarity assuming a Schottky-like thermionic emission with injection controlled by the interface and the drift controlled by the bulk. The height of the potential barrier at the Nb:SrTiO3-Bi1-xGdxFeO3 interface increases with Gd doping. The results are explained by the partial compensation of the p-type conduction due to Bi vacancies with Gd doping in addition to the shift of the Fermi level towards the middle of the bandgap with increasing dopant concentration

Misfit dislocations in nanoscale ferroelectric heterostructures

We present a quantitative study of the thickness dependence of the polarization and piezoelectric properties in epitaxial (001) PbZr0.52Ti0.48O3 films grown on (001) SrRuO3-buffered (001) SrTiO3 substrates. High-resolution transmission electron microscopy reveals that even the thinnest films (similar to 8 nm) are fully relaxed with a dislocation density close to 10(12) cm(-2) and a spacing of approximately 12 nm. Quantitative piezoelectric and ferroelectric measurements show a drastic degradation in the out-of-plane piezoelectric constant (d(33)) and the switched polarization (DP) as a function of decreasing thickness. In contrast, lattice-matched ultrathin PbZr0.2Ti0.8O3 films that have a very low dislocation density show superior ferroelectric properties. Supporting theoretical calculations show that the variations in the strain field around the core of the dislocation leads to highly localized polarization gradients and hence strong depolarizing fields, which result in suppression of ferroelectricity in the vicinity of a dislocation. (c) 2005 American Institute of Physics