Czesław Pawlaczyk

Dielectric behaviour of the new ferroelectric (CH3NH3)5Bi2Br11 in the microwave region

Abstract Low frequency dielectric measurements reveal two phase transitions in (CH3NH3)5Bi2Br11: at 311.5 K and 80 K. In the very vicinity of the ferroelectric phase transition at Tc = 311.5 K a nearly perfect Debye relaxation in the MHz region, with a critical slowing down of the relaxation frequency fe= ½πτe has been found. Well-marked deviations from this behavior in the GHz range can be interpreted as the influence of another relaxational contribution to the permittivity.

Structure, hydrogen bond network and proton conductivity of new benzimidazole compounds with dicarboxylic acids

Dicarboxylic acids are interesting for crystal engineering due to their ability of hydrogen bond formation. To find a relationship between the molecular structure and the properties of proton conducting materials, we synthesized two compounds of benzimidazole with dicarboxylic acids of different chain length: glutaric and pimelic acids. The structure of the compounds was determined by X-ray diffraction and compared with molecular arrangement studied by 13C CP/MAS NMR spectroscopy supported by Density Functional Theory computations for benzimidazole. Benzimidazole was found to form salt with glutaric acid in a 1 : 1 ratio and monoclinic layer-type structure with P21/n space group. Flat layers, parallel to (−102) plane, are built of glutaric acid molecules linked into rectangular-type chains by O–H⋯O bonds and benzimidazole molecules attached to the chains by N–H⋯O bonds. The molecule of the benzimidazole compound with pimelic acid contains two benzimidazole rings and one pimelic acid chain. The structure with alternating layers, built of two groups of benzimidazole dimers and layers of pimelic acid chains, belongs to P21/n space group. The acid layers are built of pimelic acid molecules linked by O–H⋯O hydrogen bonds into chains parallel to [30−1] direction and the benzimidazole dimers are linked to the acid layers by N–H⋯O bonds. Impedance spectroscopy studies in wide frequency and temperature range of pellets made of powdered compounds enabled to separate the contributions of crystalline and grain boundary parts to the electric conductivity. The conductivity (averaged over all directions) of the crystalline compounds of benzimidazole with glutaric and pimelic acid is characterized by activation energy of 2.5 eV and 1.6 eV, respectively, which is in an agreement with the hydrogen bond network in the materials.

Superionic phase transition in CsHSeO4 and CsDSeO4single crystal

Abstract Deuterization of CsHSeO4 does not affect of the superionic phase transition but increases the activation energy in the superionic phase.

Dielectric dispersion in the new ferroelectric CH3NH3AlCl4

Abstract The dielectric behaviour of CH3NH3AlCl4 has been studied within the frequency range from 1 kHz to 10 GHz. The dielectric dispersion near the phase transition at 100 K has a relaxational character with a relaxation time showing a critical slowing down. In the ferroelectric phase a distinct dispersion due to movements of domain walls has been found. In the lower frequency range the system is very sensitive to the strength of the measuring field.

Radiation damage in triglycine sulfate due to monoenergetic electrons

In triglycine sulfate (TGS), subjected to irradiation with a beam of monoenergetic electrons in a Van de Graaff accelerator, the dependence of an internal bias Eb and a shift ΔTemax to temperature of the electric permittivity maximum on the incident electron energy [image omitted]0 and the thickness d of the sample were measured. It is found that the penetration range of the electrons can be determined by measuring the thickness dependence of ΔTemax Losses in energy of electrons and effective cross-sections for displacement of the various atomic species in TGS were calculated. Results lead to the conclusion that up to [image omitted]0 = 0.33 MeV ionization is decisive in causing radiative defects in TGS whereas above 0.33 MeV displacement of atoms from their equilibrium positions in the lattice also contributes significantly.

Domain wall dielectric response in the phase transition region in some ferroelectrics

Abstract Properties of two dielectric contributions (I and II) observed in the phase transition region, are presented for a displacive ferroelectric TSCC and for a order-disorder ferroelectric TGS. Order clusters are discussed to be origin of both contributions.

Morphology, molecular dynamics and electric conductivity of carbohydrate polymer films based on alginic acid and benzimidazole.

The present paper describes a preparation method and molecular investigations of new biodegradable proton-conducting carbohydrate polymer films based on alginic acid and benzimidazole. Electric conductivity was studied in a wide temperature range in order to check the potential application of these compounds as membranes for electrochemical devices. Compared to pure alginic acid powder or its film, the biodegradable film of alginic acid with an addition of benzimidazole exhibits considerably higher conductivity in the range above water boiling temperature (up to approximately 10(-3) S/cm at 473 K). Due to this important feature the obtained films can be considered as candidates for application in high-temperature electrochemical devices. The microscopic nature and mechanism of the conduction in alginate based materials were studied by proton nuclear magnetic resonance (NMR). The results show specific changes in morphology and molecular dynamics between pure alginate powders and the films obtained without and with the addition of benzimidazole molecules.

Dynamic dielectric behaviour of (CH3NH3)5Bi2X11 (X:Br. CI) single crystals

Abstract The dielectric relaxation of the (CH3NH3)5Bi2X11, (X:Br, Cl) single crystals has been studied in the frequency range from 100 Hz to 20 GHz between 60 K and 400 K and from 18 to 40 GHz and 60 to 90 GHz near room temperature. Three relaxators have been found to determine the dielectric behaviour of the crystals: a critically temperature dependent Δe1 and a thermally activated Δe2 near the high temperature phase transition TC1 and another critically temperature dependent Δe3 at the low temperature phase transition. Ordering and/or freezing processes of the CH3NH3 + - dipoles are suggested to be responsible for the dielectric behaviour of these crystals.

Dielectric relaxation and conformational disorder in P(VDF/TrFE)(50/50) copolymer films irradiated with fast electrons

Relaxor-like dielectric response was observed in ferroelectric P(VDF/TrFE)(50/50) films irradiated with 1.0 and 1.5 MeV electrons and related to the results of ESR, IR and NIR Raman studies of radiation damage of the copolymer. The origin of the strong dielectric dispersion below the permittivity maximum and the frequency dependence of the temperature of ϵmax is rather complex: radiation-induced downward shift of the Curie point results in an overlapping of the dielectric anomalies at TC and at the glass transition and moreover, the dispersion is enhanced by the contribution of polar clusters consisting in short-range coherence of trans conformations. The single and conjugated C=C bonds, appearing as a result of the decay of free radicals created by incident electrons, cut ferroelectric all-trans conformation of the copolymer chains into polar clusters of short trans coherence.

Protonic Conductivity in Li(N2H5)SO4 Single Crystals

Complex impedance of Li(N2H5)SO4 was measured in the frequency range 20 Hz\div500 KHz from 290 K to 455 K. Our results confirm the model of one dimensional protonic conduction with extrinsic barriers related with defects proposed by Schmidt et al. An activation energy of 0.48 eV is assigned to the extrinsic c-axis protonic conduction, whereas 0.35 eV refers to the intrinsic conduction. There is an indication of a structure change at ~433 K.