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The influence of a disorder in cation substructure on proton conductivity of imidazolium malonate (Im‐MAL) is studied. Imidazolium in salts with dicarboxylic acids have been found to have a well ordered hydrogen‐bond network and only in Im‐MAL [Pogorzelec‐Glaser et al. (2006). Mater. Sci.‐Pol. (2006), 24, 245–252] were two types of cation observed: ordered Im‐I and disordered Im‐II. Im‐I is involved in hydrogen bonds with malonic acid molecules, whereas Im‐II is disordered between two symmetrically equivalent positions with occupancy of 0.5. NMR studies by Mizuno et al. [Hyperfine Interact. (2015), 230, 95–100] showed an 180° flip of ordered Im‐I and calculated contribution of Im‐I flipping to proton conductivity of Im‐MAL. Ławniczak et al. [Solid State Ionics (2017), 306, 25] reported that temperature variation of the proton conductivity by impedance spectroscopy yielded the conductivity value higher than that calculated by Mizuno for Im‐I. Moreover these detailed structure studies at 240 K and 280 K excluded any phase transition. Repeated X‐ray studies from 14 K to 360 K show a continuous increase in anisotropic displacement factors. The half‐occupied hydrogen bonds linking the Im‐II nitrogen atoms with hydroxyl oxygen atoms may be considered as electric dipoles and the interbond proton transfer as dipolar switching. It assumed here a coherent switching at low temperatures and a decrease of the coupling at higher temperatures with the disappearance at cross‐over temperature at 318 K. The possible proton pathway in the crystal structure is determined and the contribution of the proton dynamics of Im‐II to phonon‐assisted proton diffusion in the ordered substructure is estimated. [ABSTRACT FROM AUTHOR]

(Bi1–xLaxFeO3)0.5(PbTiO3)0.5solid solution obtained by mechanochemical synthesis was characterized by X-ray diffraction (XRD), atomic force microscopy and Fourier transform near-infrared Raman spectroscopy. The single-phase solid solution with La content betweenx= 0 and 0.5 was prepared. The solid solution exhibits a tetragonal symmetryP4mmfor 0 ≤x≤ 0.2. It was found that Raman spectra undergo a significant change for the solid solution with La content betweenx= 0.16 and 0.20. It may indicate the existence of a morphotropic boundary in this range of the La content. Detailed XRD study on (Bi0.5La0.5FeO3)0.5(PbTiO3)0.5pointed to a rhombohedral symmetryR3c. [ABSTRACT FROM AUTHOR]

In this article, we present results of field cooled (FC) and zero field cooled (ZFC) magnetization measurements and investigation of aging and memory effect in bismuth ferrite (BFO) multiferroic micro-cubes obtained by means of simple microwave synthesis procedure. It is found that difference between FC and ZFC magnetizations appear at the temperature of freezing of ferromagnetic domain walls. The decay of the magnetic momentversustime described by power-law relation and the absence of memory effect are caused by domain growth mechanism rather than by the spin-glass phase. The negligible value of remnant magnetic moment indicates that BFO compound exhibits low concentration of ferromagnetic domains and can be close to ferromagnetic to spin-glass transition. [ABSTRACT FROM PUBLISHER]

Local resistive switching was observed using AFM equipped with conducting tip addressing ∼15 unit cells in high-quality BiFeO3single crystal grown from a non-stoichiometric melt. The switching appeared under high-vacuum conditions above 340 K and the studies at various temperatures yield the activation energy of 0.74 eV. The field-induced changes in the resistivity were ascribed to the presence of localized oxygen vacancies as a consequence of the mixed valence of Fe2+/Fe3+ions. [ABSTRACT FROM AUTHOR]

The dynamics of segmental and chain motions in poly(vinylidene fluoride) confined to anodized aluminum oxide nanopores by melt-wetting was studied by broad-band dielectric spectroscopy. Molecular structure of the confined polymer was studied by means of wide-angle X-ray scattering in the transmission mode with ψ scanning. The confined polymer was found to form multilayered cylindrical mesostructure containing three polymorphs with the <020> direction of nonpolar polymorph II aligned along the pore channels. The relaxation rates of segmental motions in the amorphous phase of the polymer were found to be shorter in confined geometry than in the bulk, whereas the relaxation of the local mode was found to be broadened due to inhomogeneous relaxation times in the pores. [ABSTRACT FROM PUBLISHER]

We present the first results of FT NIR Raman studies of (K0.5Na0.5NbO3)1 - x(SrTiO3)x (x = 0.25, 0.20, 0.15) relaxors made in wide temperature range. Although the crystal structure of the investigated relaxors exhibits a pseudocubic symmetry Raman spectra are observed. The Raman spectra of (K0.5Na0.5NbO3)1 - x(SrTiO3) solid solution resemble those observed for orthorhombic K0.5Na0.5NbO3. The results are discussed in the frame of molecular dynamics of NbO6 octahedral network. It was found that, the changes in dynamics of NbO6 molecular groups appear at T ≈ 196 K for x = 0.25, T ≈ 254 K for x = 0.20 and T ≈ 336 K for x = 0.15. [ABSTRACT FROM AUTHOR]

K 1- x Na x NbO 3 is considered as an alternative system for lead-based functional ceramics widely used in transducers, sensors and actuators. In some applications however, the composites of electroactive ceramic and polymer, with low acoustic impedance and dielectric permittivity that can be tailored to various requirement, are more useful. We studied dielectric relaxation processes in polyvinylidene fluoride (PVDF) loaded with K 0.5 Na 0.5 NbO 3 powder in wide temperature and frequency range. The powder was prepared by solid state synthesis and characterized by HRTEM and NIR Raman spectroscopy. The dielectric response of (K 0.5 Na 0.5 NbO 3 ) 0.32 (PVDF) 0.68 composite, of (0–3) connectivity, was found to be determined by the relaxation processes of the polymer matrix with an additional broad low-frequency anomaly at &nvsim; 305 K that we relate to a response of water absorbed by the shell of KNN grains. [ABSTRACT FROM AUTHOR]

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 ℇ max is rather complex: radiation-induced downward shift of the Curie point results in an overlapping of the dielectric anomalies at T C 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. [ABSTRACT FROM AUTHOR]

Dielectric response (100 Hz-1 MHz) and pyroelectric response (light modulation frequency range 10 Hz-1 kHz) of ferroelectric P(VDF/TrFE)(50/50) copolymer loaded with relaxor PLZT 9.5/65/35 ceramic powder of 10 nm crystallite size and ∼700 nm aggregates was studied. Though the dielectric permittivity of the composites increases due to high permittivity of the ceramic, their dielectric response is determined by dielectric relaxation processes of the polymer matrix. The dispersive dielectric anomalies of PLZT-0.9/65/35 relaxor ceramic affect mainly the dielectric absorption of the composites in the range of dipolar relaxation in the crystallite phase of the copolymer. The composites exhibit pyroelectric activity proper for application in operation frequency up to 1 kHz and temperature range 290-310 K. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue. Articles published within the issue were taken from the XVII Czech -- Polish Seminar held in Znojmo, Czech Republic on May 22-26, 2006. The topics covered include the physics of the ferroelectrics and relaxor ferroelectrics with perovskite structure as well as phase transitions, aspects of ferroelectricity and structural phase transitions.

Abstract: Rb3D(SeO4)2 belongs to the well-known group of hydrogen sulfate and selenate crystals which are promising for fuel cell applications. However, the high temperature properties of this salt have been much less extensively studied than those of Rb3H(SeO4)2. Superionic phase transition in Rb3D(SeO4)2 and Rb3H(SeO4)2 single crystals was studied using impedance spectroscopy and DSC methods. Temperature evolution of the ferroelastic domain structure was observed under a polarizing microscope. Additionally, the X-ray diffraction and Raman scattering measurements for both crystals were carried out at room temperature. Rb3D(SeO4)2 undergoes a structural phase transition from the low temperature ferroelastic phase to the superionic, paraelastic one. A correlation was found between the ferroelastic domains evolution, the anomalies of DSC and the temperature dependence of ionic conductivity. The temperature range of superionic phase transition in the first heating run was much wider and the T S value was lower in Rb3D(SeO4)2 than in the non-deuterated compound. Additionally, a considerable temperature hysteresis of T S in Rb3D(SeO4)2 was observed, unlike in Rb3H(SeO4)2. The activation energies of H+ and D+ conductivity along the c-axis were found to be almost the same. The temperature variation of ionic conductivity in Rb3D(SeO4)2 obtained in the first heating run of a virgin sample was found to differ considerably from that measured in subsequent cooling/heating runs. The small H/D isotope effect of proton conductivity in the crystals studied pointed to a classical activated diffusion mechanism. [Copyright &y& Elsevier]

Cd(2)Nb(2)O(7) is still an interesting ferroelectric material because of its high permittivity value at helium temperatures and a variety of dielectric relaxation processes, the origin of which is still puzzling. We prepared hot-pressed ceramics, with grain sizes from 100 to 150 nm, obtained from Cd(2)Nb(2)O(7) nanopowders synthesized by high-energy milling of CdO and Nb(2)O(5) and studied their dielectric response and thermal properties. The nanoceramics were characterized by X-ray diffraction and their dielectric properties were measured at temperatures from 4K to 575K. Dielectric response of the nanoceramics was found to consist of a huge anomaly at ~150K with complex dielectric absorption and three relaxation processes apparent in frequency and temperature dependences of the imaginary part of permittivity in the temperature range from 18K to 145K. The anomaly at ~150K is related to overlapping contributions from the Curie point (shifted downward because of the size effect) and a dielectric relaxation process. The behavior of three relaxation modes observed at temperatures below 145K is discussed, based on the model proposed by Malcherek of polar nanoregions in the orthorhombic phase of Cd(2)Nb(2)O(7) and the theory of dielectric response of ferroelectric relaxors by Bokov and Ye.