Mirosław Gałązka

Structure–property relationships in hybrid (C3H5N2)3[Sb2I9] and (C3H5N2)3[Bi2I9] isomorphs

Two hybrid crystals imidazolium iodoantimonate(III) and iodobismuthate(III), (C3H5N2)3[Sb2I9] (ImIA) and (C3H5N2)3[Bi2I9] (ImIB), have been synthesized and characterized in a wide temperature range (100–350 K) by means of X-ray diffraction, dielectric spectroscopy, proton magnetic resonance (1H NMR), FT-IR spectroscopy and optical observations. They undergo two temperature induced solid–solid structural phase transitions. The first one, quasi-continuous (with temperature hysteresis below 1 K), occurs at 324 K in ImIA and 327 K in ImIB, and the second one, clearly of the first order, at 273/278 (cooling/heating) and 291/295 K, in ImIA and ImIB, respectively. Ferroelastic properties are maintained in low-temperature phases. Both materials are isomorphic in the corresponding phases. High temperature phase I has a hexagonal P63/mmc symmetry, and phase II has orthorhombic Cmcm. The crystal architecture is composed of discrete, face-sharing bioctahedra [M2I9]3− (M: Sb, Bi) and imidazolium cations which are highly disordered over phases I and II. The dynamics of the imidazolium cations has a prominent impact on the stability of the particular phases.

Strong Improper Ferroelasticity and Weak Canted Ferroelectricity in a Martensitic-Like Phase Transition of Diisobutylammonium Bromide

Diisobutylammonium bromide is found to be a unique improper ferroelastic in which the elastic degrees of freedom seem to play the essential role, giving rise to a domain pattern resembling that of martensitic phase transitions. A weak canted ferroelectricity turns out switchable by an electric field.

Critical Behaviour in Ferroelectrics as Studied by Nonlinear Dielectric Effect. Invariants of the Electric Susceptibility in a Biasing Field

The simplest equation of state compatible with the Widom and Griffiths scaling hypothesis have been built for the uniaxial ferroelectrics TGS and MAPCB. The explicit forms have been found of the scaling invariants deduced from the curves of the electric susceptibility measured in a constant biasing field. Smooth and sharp inflection points of the susceptibility curve in the vicinity of the critical temperature have been classified. The invariants and the inflection points have been used to determine critical parameters of TGS and MAPCB.

Unified description of nonclassical uniaxial ferroelectric materials in order–disorder phase transitions

An equation of state accounting for coupling of the primary order parameter (here the polarization) with a secondary order parameter (here a strain ϵ) is used to describe the temperature dependences of the spontaneous polarization and of the electric susceptibility on external biasing field. A new scaling invariant and its explicit expression are given. The theory is exemplified by the effective critical behavior of the molecular ferroelectric crystals (CH3NH3)5Bi2Cl11 (MAPCB) and (CH3NH3)5Bi2Br11 (MAPBB).

On the ratio of Curie--Weiss constants in ferroelectrics undergoing second order phase transitions

Scaling hypothesis is used to construct the equations of state that provide the experimentally observed variety of the Curie--Weiss constants ratios (i.e., the ratios of the slopes between the temperature dependencies of inverse of susceptibility below and above the critical point) in uniaxial ferroelectrics. The results are exemplified by the TGS crystal and by the methylammonium salts MAPCB and MAPBB.

Scaling equation of state for uniaxial ferroelectrics: zero-field susceptibility and NDE effect

The simplest scaling equation of state and its limit case corresponding to the Landau theory turns out to accurately describe the temperature dependence of the electric susceptibility measured in a biasing static field (Nonlinear Dielectric Effect NDE) in uniaxial ferroelectrics. The same equation of state should be, in principle, valid at the zero-biasing field, in which case the susceptibility is singular , where Γ+ and Γ− are the inverse Curie–Weiss constants at T > T C and T < T C, respectively. The simplest scaling equation of state implies the ratio Γ−/Γ+ = δ − 1, where δ is a critical exponent: δ = 3 in the Landau theory. However, the real experimental data show serious discrepancies with this prediction even in systems following the Landau theory. We show how to improve the equation of state without infringing the scaling hypothesis so that this discrepancy is removed. An interesting result of the proposed modification is that the deviation of Γ−/Γ+ from δ − 1 is a signature of the critical exponent γ being different from 1. The experimental data on the uniaxial ferroelectrics MAPCB and MAPBB will be used as examples of the treatment.

Phase sequence in diisopropylammonium iodide: avoided ferroelectricity by the appearance of a reconstructed phase

Crystals of diisopropylammonium iodide are synthesized, grown and characterized. Two phases: P21/m (Z = 1) and P212121 (Z = 2) are observed. In contrast with analogous compounds no polar phase occurs, despite a critical-like electric behaviour. A phenomenological theory is proposed to describe the thermodynamics of the whole family of diisopropylammonium halides.

Protective properties of the arterial system against peripherally generated waves

An anatomically detailed model consisting of a network of electric transmission lines is developed to simulate propagation of the pulse waves in humans. The simulations show that the real arterial tree geometry, together with the elastic and rheological parameters of particular segments, ensure an efficient protection of vital organs against pulse waves generated at peripheral locations. Because locomotive movements are the most obvious source of such disturbances, additional cyclic perturbations are applied to the model femoral arteries. It is shown that the impact of such peripherally generated pulse waves onto the pressure profiles at the ascending aorta and at other vital locations of the system is surprisingly weak independently of synchronization/desynchronization with the heart action period. This may witness to an intrinsically protective nature of the arterial tree anatomy in addition to its known functionality of the optimal blood supply at possibly low lumen volume. The extent of the protection is also studied in the presence of a complete arterial embolism at the left common carotid artery.

Universal scaling of dielectric response of various liquid crystals and glass-forming liquids

Abstract We present a new generalized scaling relationship accounting both for the real and imaginary parts of the complex permittivity data. The generalized scaling procedure has been successfully used for various relaxation processes in liquid crystals (4-bromobenzylidene-4′-pentyloxyaniline, 4-bromobenzylidene-4′-hexyloxyaniline, 4′-butyl-4-(2-methylbutoxy)-azoxybenzene, 4-ethyl-4′-octylazoxybenzene), and in glass-forming liquids (glycerol, propylene carbonate, salol, cresolphthalein-dimethylether). As it is shown, one obtains common master-curve for liquid-like phases (isotropic liquid, cholesteric, nematic, smectic A), solid-like phases (smectic B, conformationally disorder crystal) and supercooled liquid phase.

Phonon Mode Conversion at Planar Interfaces in Crystalline Solids. Harmonic and Anharmonic Interface Potentials

A generalized model of a solid-solid interface is built. The model takes into account additional surface mass densities on both sides of the interface and an anisotropic and/or anharmonic coupling potential. The resonances due to the potential (up to three) manifest themselves by minima (zeros) of transmition and/or extrema in reflected and transmitted waves of different polarization depending on physical properties of the media and of the geometry.