The perovskites Pb(SclpNblp)O, and Pb(SclpTalp)O, can be obtained in a disordered state by means of a synthesis a t high temperature (1 250 to 1600 "C). Ordering of the trivalent and pentavalent ions occurs during annealing a t lower temperatures. The kinetics of this ordering process are investigated by means of X-ray diffraction, dielectric polarisation, and DSC measurements. The ordering pro...

In this paper we review the crystal chemistry and structure data from the literature and our results reported in the last decade for natural and synthetic samples of the tantalite-columbite series. Orderdisorder transitions and oxidation reactions on the ixiolite-columbite-wodginite system are reported for one Brazilian sample. It is shown that reports on these subjects are sometimes dubious an...

The critical behaviour of the order parameter is investigated using the birefringence and Raman intensity data near the λ-phase transition (Tλ=235 K) in NH4Br. From the analysis of the experimental data using the mean field theory, the critical exponent for the order parameter is determined as β ≈ 0.5. This indicates a second order transition between the phases II (CsCl) and III (tetragonal) in...

Long time asymptotics are developed here for an Allen-Cahn/Cahn-Hilliard system derived recently by Cahn & Novick-Cohen [11] as a di use interface model for simultaneous orderdisorder and phase separation. Proximity to a deep quench limit is assumed, and spatial scales are chosen to model Krzanowski instabilities in which droplets of a minor disordered phase bounded by interphase boundaries (IP...

Using the self-consistent field theory (SCFT) in spherical unit cells of various dimensionalities, D, a phase diagram of a diblock, A-b-B, is calculated in 5 dimensional space, d = 5. This is an extension of a previuos work for d = 4. The phase diagram is parameterized by the chain composition, f, and incompatibility between A and B, quantified by the product χN. We predict 5 stable nanophases:...

A complex system may consist of many subsystems. The dimension of the equations used to model such a system may be enormously large. It is well kown that a nonequilibrium complex system may undergo a variety of bifurcations and exhibit diverse types of self-organization behavior. It was found, however, that in the vicinity of a bifurcation point the enormous number of subsystems is governed by ...

We present several ordering mechanisms in diblock copolymers. For temperatures above the orderdisorder temperature and in the weak segregation regime, a linear response theory is presented which gives the polymer density in the vicinity of confining flat surfaces. The surfaces are chemically patterned where different regions attract different parts of the copolymer chain. The surface pattern or...

The block copolymers are an exceptional kind of macromolecules constituted by two or more blocks of different homopolymer chains linked by covalent bonds. These polymeric materials have received much attention over past few years due in large part to their ability to selfassemble in the melted state or in a selective solvent inside a variety of ordered phases or welldefined structures of high r...

In this PhD thesis, we develop models of surfaces of epitaxially grown crystals. In the introductory chapter 1, we introduce the most important physical processes which occur on crystal surfaces in a molecular beam epitaxy (MBE) environment. In the first part of this work (chapters 2–4) we model the (001) surface of the II-VI semiconductors CdTe and ZnSe, our main focus being on CdTe. In the se...

There exists a special class of solid media called soft media (or weakly compressible media), for which the inequality ┣>>┤ is satisfied (┣ and ┤ are the Lamé coefficients) [1-6]. Such media with very small shear stiffness are dynamically similar to liquids to a great extent and exhibit strongly a “water-like” characteristic and, therefore, are also associated with the name of “water-like” medi...