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Despite the current focus on the electronic properties of GaV4S8 lacunar spinel, the microstructural and mechanical characterization of this material is scarce in the literature. In this work, we propose an effective GaV4S8 ceramics production method and provide a detailed microstructural and micromechanical characterization. Light microscopy, scanning electron microscopy and X-ray diffraction are used to describe the microstructure of the ceramic targets that can be used for thin film deposition. V2O3 was found to be the main impurity in ceramic targets and its content is discussed with respect to the sintering atmosphere control. Nanoindentation and microcantilever bending were employed to provide estimates of the indentation modulus, hardness and fracture stress of individual grains. The values of these parameters have been determined as Er = 130 ± 2 GPa, H = 8.9 ± 0.2 GPa and σc = 600 ± 57 MPa, respectively.

We have studied several unfilled tetragonal tungsten-bronze crystals (SBN-35, CBN-28, CBN-30, CBN-32) by differential scanning calorimetry, Brillouin spectroscopy and piezoresponse-force microscopy...

The room temperature structure with P21/c symmetry of the zinc(II) complex of pyridine-2,6-dicarboxylic acid was published by Okabe and Oya (N. Okabe, N. Oya, Copper(II) and zinc(II) complexes of pyridine-2,6-dicarboxylic acid. Acta Crystallogr. C. 2000, 56, 305). Here we report crystal structure of the low temperature phase β-[Zn(pydcH)2]·3H2O, pydc=C7H3NO4, resulting from the phase transition around 200K. The diffraction pattern of the low temperature phase revealed satellite reflections, which could be indexed with q-vector 0.4051(10)b* corresponding to (3+1)D incommensurately modulated structure. The modulated structure was solved in the superspace group X21/c(0b0)s0, where X stands for a non-standard centring vector (½, 0, 0, ½), and compared with the room temperature phase. It is shown that hydrogen bonds are the main driving force of modulation.

BaTiO3 (BTO) layers were deposited by pulsed laser deposition (PLD) on TiNb, Pt/TiNb, Si (100), and fused silica substrates using various deposition conditions. Polycrystalline BTO with sizes of crystallites in the range from 90nm to 160nm was obtained at elevated substrate temperatures of (600°C-700°C). With increasing deposition temperature above 700°C the formation of unwanted rutile phase prevented the growth of perovskite ferroelectric BTO. Concurrently, with decreasing substrate temperature below 500°C, amorphous films were formed. Post-deposition annealing of the amorphous deposits allowed obtaining perovskite BTO. Using a very thin Pt interlayer between the BTO films and TiNb substrate enabled high-temperature growth of preferentially oriented BTO. Raman spectroscopy and electrical characterization indicated polar ferroelectric behaviour of the BTO films.

Neutron pair distribution function analysis and first principles calculations have been employed to study short-range correlations in heavily disordered dielectric material Sr$_x$Ba$_{1-x}$Nb$_2$O$_6$ ($x=0.35, 0.5$ and 0.61). The combination of methods has been fruitful in pinpointing main local-structure features, their temperature behaviour and interrelation. A rather complex system of tilts is found to be both temperature and Sr-content sensitive with the biggest tilt magnitudes reached at low temperatures and high $x$. Relative Nb-O$_6$ displacements, directly responsible for material's ferroelectric properties, are shown to be distinct in two octahedra sub-systems with different freezing temperatures and disparate levels of deviation from macroscopic polarization direction. Intrinsic disorder caused by Sr, Ba and vacancy distribution is found to introduce local strain to the structure and directly influence octahedra tilting. These findings establish a new atomistic picture of the local structure -- property relationship in Sr$_x$Ba$_{1-x}$Nb$_2$O$_6$.

BaTiO3 films deposited onto TiNb and Ti substrates using hydrothermal synthesis method were studied in the presented work. These films are supposed to improve properties of bone implants due to their ferroelectric behaviour, because ferroelectrics induce improved bone formation. A great question is the chemical stability of the used material. It can be crucial for its biocompatibility and possible in vivo application. We studied chemical composition of prepared samples, especially concentration of Ba and Ti and trends of these concentrations stimulated by a solution saline action. The Ba and Ti concentrations were determined by XPS under ultra - high vacuum condition. The BaTiO3 films were investigated as received after the preparation procedure as well as after a long - time treatment in solution saline. Every sample was introduced to the solution saline at first for 1 and later for 3 weeks. Ti concentration almost does not change during our experiments while a meaningful Ba decrease is observed. Nevertheless, barium release seems to slow down with respect to the time of solution saline action. Stability of barium titanate films in a period of several months and an absolute amount of the released barium will be a subject of the next research.

The broadband dielectric response of the uniaxial ferroelectric strontium barium niobate with 35% Sr has been studied from 1 kHz to 30 THz along the polar $c$ axis using high-frequency and low-frequency dielectric spectroscopies, time-domain terahertz spectroscopy, and far-infrared reflectivity, in the wide temperature interval 20--600 K. The mechanisms that contribute to the ferroelectric phase transition and to the dielectric anomaly in this material are the softening of an anharmonic excitation in the THz range related to cation hopping and the slowing down of a relaxation in the GHz range, which saturates below ${T}_{\mathrm{C}}$ near 1 MHz. In the ferroelectric phase, a relaxation, related to domain-wall dynamics, appears in the sub-GHz range and hardens on cooling up to 10 GHz. The ferroelectric-paraelectric transition, investigated by electron diffraction, has been assessed to the appearance of a supplementary mirror plane perpendicular to the polar axis.

Dielectric and magnetic properties of Eu0.5Ba0.25Sr0.25TiO3 are investigated between 10 K and 300 K in the frequency range from 10 Hz to 100 THz. A peak in permittivity revealed near 130 K and observed ferroelectric hysteresis loops prove the ferroelectric order below thistemperature. The peak in permittivity is given mainly by softening of the lowest frequency polar phonon (soft mode revealed in THz and IR spectra) that demonstrates displacive character of the phase transition. Room-temperature X-ray diffraction analysis reveals cubic structure, but the IR reflectivity spectra give evidence of a lower crystal structure, presumably tetragonal I4/mcm with tilted oxygen octahedra as it has been observed in EuTiO3. The magnetic measurements show that the antiferromagnetic order occurs below 1.8 K. Eu0.5Ba0.25Sr0.25TiO3 has three times lower coercive field than Eu0.5Ba0.5TiO3, therefore we propose this system for measurements of electric dipole moment of electron., Phase Transitions, in press

In this study, ceramic samples of lead zirconate titanate Pb(Zr0.42Ti0.58)O3 (PZT 42/58) doped with Fe (hard) and Nb (soft) were studied by Raman, infrared (IR) and THz spectroscopy in the temperature range from 900 to 20 K. From the evaluation of the IR and Raman phonons in undoped ceramics, we conclude that tetragonal PZT ceramics undergo a low-temperature phase transition to a tilted phase, revealed by anomalies in phonon parameters and the appearance of new modes. Doped samples also presented similar behaviour. The main differences between undoped and doped ceramics lie in the dielectric behaviour below phonon frequency range, where several mechanisms appear: a soft central mode (CM) located near 1 THz and two relaxations in the GHz range. Both types of doping raise the permittivity values below the phonon frequencies, not only increasing the dielectric contribution of the CM, but also modifying the dielectric response near the GHz range. Soft ceramics show higher permittivity with logarithmic increas...

Using the sol-gel technique, BaTiO3 was embedded into nanoporous Vycor and artificial vitreous opal silica for the first time. About 50 vol% of the pores was filled. In case of the Vycor glass (pore diameter 4-6 nm) only amorphous phase was revealed by XRD, IR reflectivity and Raman spectra. After additional gradual annealing, no crystallization was achieved. Chemical reaction with the SiO2 skeleton started at ~1000 K. The room-temperature IR and Raman spectra clearly show characteristic vibrational modes of the ferroelectrically distorted TiO6 octahedra without any long-range order. In case of the opal matrix (densely packed silica spheres, pore diameter up to ~50 nm), crystallization of the ferroelectric BaTiO3 appeared in coexistence with the amorphous phase, but the penetration depth of the crystalline BaTiO3 was limited. From the apparent temperature independence of the effective wide-frequency dielectric response due to the essentially temperature independent effective soft mode stiffened to ~100 cm-1, we can deduce that no macroscopic percolation of the crystalline BaTiO3 has appeared in our opal matrix. Nevertheless, Raman spectra bring evidence of a diffuse ferroelectric phase transition in the opal-BaTiO3 composite.

Infrared reflectivity spectra of antiferromagnetic incipient ferroelectric EuTiO3 were investigated up to 600 K. Three polar phonons typical for the cubic perovskite $Pm\bar {3}m$ structure were observed. Analysis of phonon plasma frequencies showed that the lowest-energy TO1 phonon corresponds predominantly to the Slater mode describing vibration of Ti cations against the oxygen octahedra and the TO2 phonon expresses vibrations of the Eu cation against the TiO6 octahedra. The highest frequency TO4 phonon represents O-octahedra bending. Incipient ferroelectric behavior of the permittivity is caused by pronounced softening of the TO1 phonon, which is coupled to the TO2 mode. Although the Eu cations are not involved in the TO1 mode, the spin ordering of the 4f electrons at Eu cations has influence on the frequency of the TO1 mode due to Eu-O-Eu super-exchange interaction. This is probably responsible for the 7% change of the permittivity induced by the magnetic field in the antiferromagnetic phase, as reported by Katsufuji and Takagi [Phys. Rev. B 64, 054415 (2001)].

The dielectric behaviour of tetragonal PLZT x/40/60 ceramics doped with lanthanum (x = 5, 12 and 15%) has been investigated at 100–1014 Hz. Dielectric, THz and infrared spectra were measured from 500 to 20 K. For x ≥ 12 relaxor ferroelectric behaviour was observed. All three samples showed an additional relaxational mode below phonons. Analysis of the phonon modes for ferroelectric PLZT 5/40/60 is presented together with the complete dielectric behaviour.

Potassium tantalum niobate (KTa x Nb 1− x O 3 , (KTN), where x = 0, 0.21, 0.36, 0.53, 0.74, 0.82, 0.86, and 1) thin films were prepared by chemical solution deposition (CSD) on Si substrates. A homogeneous and stable sol was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol, refluxing for 30 min and adding diethanolamine as a modifier. The sol was deposited by spin coating. KTN perovskite films were successfully prepared only on substrates covered with Al 2 O 3 “chemical” and KNbO 3 seeding buffer layers, otherwise a pyrochlore structure was preferred. Annealing temperature and heating regime were also important factors for film quality. The powder X-ray diffraction confirmed that the prepared films had pseudocubic perovskite structure. The infrared transmittance spectrum of the films for high concentration of Ta shows three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with those for the bulk m...

Potassium tantalate KTaO3, (KT) thin films of perovskite structure were prepared by chemical solution deposition (CSD) on Si and SiO2 glass substrates. Potassium and tantalum isobutoxides were dissolved in absolute isobutanol with an addition of diethanolamine as a modifier to obtain a homogeneous and stable precursor solution. Optimum conditions for film preparation were found. Annealing temperature and heating regime, Al2O3 “chemical” buffer layer and KNbO3 seeding layer were the determining factors of the film quality. It was demonstrated by X-ray diffraction (XRD) that the films have the desired cubic perovskite structure. The infrared transmittance spectrum of the films shows three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with the bulk material, except the 14 cm−1 shift of the lowest phonon, which has been also observed in other perovskite materials. The temperature dependence of the phonon parameters has been studied too.

Potassium tantalate niobate (KTaxNb1−xO3, (KTN), where x = 0, 0.21, 0.36, 0.53, 0.74, 0.82, 0.86, and 1) thin films of perovskite structure were prepared by chemical solution deposition (CSD) on Si and SiO2 glass substrates. A homogeneous and stable precursor solution was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol and an addition of diethanolamine as a modifier. The film quality was determined by annealing temperature and heating regime, Al2O3 “chemical” buffer layer and KNbO3 seeding layer. Optimum conditions for film preparation were found. It was approved by X-ray diffraction (XRD) that the films have the wanted pseudocubic perovskite structure. Infrared transmittance was measured for broad range of Ta/Nb ratios. The spectra show continuous transformation from KTaO3 to KNbO3 and indicate that the optical axis lies in the plane of the film.

Potassium tantalate (KT) KTaO 3 thin films of both pyrochlore and perovskite cubic structures were prepared through the chemical solution deposition (CSD). A homogeneous and stable precursor solution was obtained from potassium iso-butoxide and tantalum iso-butoxide in absolute iso-butanol with an additive of diethanolamine as a stabilizer. The effects of K:Ta sol stoichiometry, type of substrate (both amorphous, and single crystal substrates), type of buffer interlayer [Al 2 O 3 , Y-stabilized ZrO 2 (YSZ), PbTiO 3 , PbTiO 3 –Al 2 O 3 composite, KNbO 3 (KN)], and annealing regime on the kinetics of pyrochlore to perovskite transition has been studied. KT perovskite films have been successfully prepared on (100)MgO, and (0001)Al 2 O 3 . Using SiO 2 and Si substrates, perovskite films have been obtained via insertion of Al 2 O 3 and KNbO 3 buffer layers.

A series of SiO2/KHSO4 nanocomposites with various SiO2/salt ratios was prepared where the active compound was added before gelation. The sol was prepared by mixing of these hydrogen salts, TEOS (tetraethyl orthosilicate) and water. After gelation and heat treatment (heating slowly to 200–220°C under vacuum), the samples were characterized by X-ray diffraction, Differential Scanning Calorimetry (DSC), IR spectroscopy, Scanning Electron Microscopy (SEM), and High Resolution Transition Electron Microscopy (HR TEM). DSC measurements showed phase transition temperature shifts that depended on the SiO2/salt ratio. The properties of the nanocomposite samples were compared with the bulk materials. The shift in the phase transitions to lower temperatures was attributed to the particle size effect.

The thin-films of BaTiO3 (BTO)/Pt were prepared to test their potential as coatings for titanium-alloy implants. The nanocrystalline BTO/Pt bi-layers were successfully synthesized using fused silica as substrates. The bi-layers were prepared using KrF excimer laser ablation at substrate temperatures (Ts) ranging from 650 °C to 750 °C. The microstructure and composition of the deposits were investigated by scanning electron microscope, x-ray diffraction and wavelength dispersive x-ray spectroscopy methods. The electrical characterization of the Pt/BTO/Pt capacitors indicated ferroelectric-type response in BTO films containing (40–140) nm-sized grains. The technology, microstructure, and functional response of the layers are presented in detail.

Spin and lattice dynamics of CaMn7O12 ceramics were investigated using infrared, THz and inelastic neutron scattering (INS) spectroscopies in the temperature range 2 to 590 K, and, at low temperatures, in applied magnetic fields of up to 12 T. On cooling, we observed phonon splitting accompanying the structural phase transition at Tc = 450K as well as the onset of the incommensurately modulated structure at 250 K. In the two antiferromagnetic phases below T_N1 = 90K and T_N2 = 48 K, several infrared-active excitations emerge in the meV range; their frequencies correspond to the maxima in the magnon density of states obtained by INS. At the magnetic phase transitions, these modes display strong anomalies and for some of them, a transfer of dielectric strength from the higher-frequency phonons is observed. We propose that these modes are electromagnons. Remarkably, at least two of these modes remain active also in the paramagnetic phase; for this reason, we call them paraelectromagnons. In accordance with this observation, quasielastic neutron scattering revealed short-range magnetic correlations persisting within temperatures up to 500K above T_N1.

The sol–gel method was used to prepare PbTiO 3 (PT) and PbTiO 3 –A1 2 O 3 (PT–AL) thin films on amorphous (SiO 2 glass) and crystalline (111) Si, and (0001) Al 2 O 3 ) substrates using the dip-coating technique. The films were examined by XRD methods to describe the phase composition, cell parameters and degree of texture, by electron microprobe, AFM, SEM, EDAX and Rutherford backscattering to evaluate the microstructure and composition. PT–AL films are stressed, have grain size smaller than 0.1 μm and modified cell parameters of PT phase (lower c / a tetragonality). In dependence on the molar ratio of Ti:Al, the different extent of crystallographic ordering was observed ranging from randomly oriented to strongly textured crystallites of PT. In the compositional range of Ti/Al 2÷4 the films show strong fibre texture with the a -axis (axis of texture) oriented perpendicular to the film plane.

High-frequency dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity e′ and Q×f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τf varies between −73 and 232 ppm/°C, and in two samples |τf| is less than 15 ppm/°C. It is shown that the microwave permittivity e′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss e″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed.

Two series of ferroelectric liquid crystalline materials, containing a lateral chlorine group on the aromatic ring of the molecular core, have been synthesised and investigated. Sequences of mesophases and phase transition temperatures have been determined for all substances. The temperature dependences of the complex permittivity and the spontaneous polarisation were determined in the whole range of the ferroelectric SmC* phase. The substitution of chlorine increases the values of spontaneous polarisation more than 5 times in comparison with non-chlorinated compounds.

The synthesis of a new heterocyclic core has been developed. Its standard derivatisation afforded new types of FLC's and their physical properties were determined.

PbTiO3 and SrTiO3 single phase films and PbTiO3−Al2O3 composite and multilayer films were prepared by the sol-gel method using dip- and spincoating deposition techniques. The films were characterized by optical microscopy. X-ray diffractometry, Alpha Step profilometer, Rutherford back-scattering and Fourier transform far infrared spectroscopy. It was found that the presence of Al2O3 in composite films blocks the PbTiO3 crystallization even at the temperature 800°C whereas in multilayer films the crystallization is retarded to a certain extent only. FT FIR spectroscopy has revealed in PbTiO3 films the well-pronounced soft mode at frequency 82cm−1 slightly lower than in bulk crystals which indicates some compressive internal stresses. In SrTiO3 films the effective soft mode damping increases with decreasing film thickness, which demonstrates the role of stresses induced by the substrate.

Physical properies of ion-conducting nanocomposites are reviewed. Special attention is paid to the change of the bulk characteristics of ionic salts in the nanocomposites due to the formation of the interface phases. The main thermodynamic reason of the formation of the nanocomposite as well as the stabilization of the interface phases is the adhesion energy σa. At sufficiently high σa values, the ionic salt tends to spread along the oxide surface, which leads to the formation of the nanocomposite on sintering. The adhesion is the result of the interface interaction and incorporates the stage of the specific adsorption of the interface ions. It leads to the formation of the double layer formed by the point defects in the interface region of the ionic salt. In the case of the strong adhesion, the structural reconstruction or the formation of the metastable interface phase takes place. Analysis of the experimental data shows that interface phases exist in composites AgI–Al2O3, MeNO3–Al2O3 (Me = Li, Na, K, Rb, and Cs), CsHSO4–SiO2, RbNO3–SiO2 and CsCl–Al2O3. Their structure may be either epitaxial crystalline, or amorphous. The thickness of the interface phase as estimated on the basis of the brick-wall model is about 3–4 nm.

AgI–Al2O3 nanocomposites are investigated by high-resolution electron microscopy and luminescence spectroscopy. The results show that both crystalline and amorphous phases coexist in AgI–Al2O3 composites. At sufficiently high alumina content, almost all AgI occurs as amorphous spherical nanoparticles distributed uniformly on alumina surfaces. The amorphous phase exhibits unusual luminescence spectra with a single, very broad nonstructured band. The amorphous phase is stabilized on AgI–alumina interfaces with the relative concentration progressively increasing with the Al2O3 fraction. The thickness of the interface amorphous layer adjacent to Al2O3 particles estimated by means of a simple brick-wall model is about 3 nm.

IR, Raman and Brillouin spectra of the fast protonic conductor Cs5H3(SO4)4 · xH2O (x ≤ 1) have been investigated in the 80-500 K (IR), 20-435 K (Raman) and 190-425 K (Brillouin) temperature range. Results of the DSC analysis are presented, which reveal a hysteresis of both the superionic and glass transition temperature. The spectra are interpreted on the basis of a factor-group analysis; the mechanism of the proton glass transition and that of the proton transport in the superionic phase are discussed. Brillouin spectra revealed a relaxation process with the frequency 1.25 × 1010 Hz at 274 K which differs from that observed in dielectric data. The former relaxation is assigned to SO4 2 reorientations, the latter to slower interbond proton hopping.

A new series of ferroelectric liquid crystal materials having the methoxy group substituted in an aromatic ring of the mesogenic core has been synthetized and characterized. This electron-donor methoxy group makes the ferroelectric S∗c phase narrower in range and monotropic when compared to the series with the unsubstituted molecules, the values of the spontaneous polarization remaining unaffected.

Room-temperature infrared (IR) reflectivity, terahertz transmission and evaluated effective complex dielectric response of four polycrystalline alumina ceramics (corundum) with highly anisotropic grains in the IR range were determined. The spectra were compared with modelled spectra based on the known IR response of sapphire single crystal and Bruggeman and Lichtenecker models of the effective medium approximation (EMA). The results are extremely sensitive to the surface treatment (polishing), but do not depend on the grain size in the range of ∼0.3–1 μm and on the weak doping, needed for processing of optically transparent ceramics. As all the samples show similar grain shapes and topology, no measurable differences among the fully dense samples were observed. Agreement with the modelled spectra is reasonable, but shows a higher effective mode damping. A weak geometrical resonance was revealed near 500 cm−1, better described by the Bruggeman model. The small sample porosity up to 6.2% is revealed mainly as a reduced reflectivity above ∼650 cm−1, which produces weak losses in the high-frequency range above the TO phonon modes, better described by the Lichtenecker model.

Ferroelectrics have been, among others, studied as electroactive implant materials. Previous investigations have indicated that such implants induce improved bone formation. If a ferroelectric is immersed in a liquid, an electric double layer and a diffusion layer are formed at the interface. This is decisive for protein adsorption and bioactive behaviour, particularly for the adhesion and growth of cells. The charge distribution can be characterized, in a simplified way, by the zeta potential. We measured the zeta potential in dependence on the surface polarity on poled ferroelectric single crystalline LiNbO3 plates. Both our results and recent results of colloidal probe microscopy indicate that the charge distribution at the surface can be influenced by the surface polarity of ferroelectrics under certain 'ideal' conditions (low ionic strength, non-contaminated surface, very low roughness). However, suggested ferroelectric coatings on the surface of implants are far from ideal: they are rough, polycrystalline, and the body fluid is complex and has high ionic strength. In real cases, it can therefore be expected that there is rather low influence of the sign of the surface polarity on the electric diffusion layer and thus on the specific adsorption of proteins. This is supported by our results from studies of the adhesion, growth and the activity of alkaline phosphatase of human osteoblast-like Saos-2 cells on ferroelectric LiNbO3 plates in vitro.

We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at T_C1=475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above T_C1. Step-like dielectric anomaly observed at T_C1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of P. Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic, but only antipolar ferromagnet., accepted to JAP

A ferroelastic phase transition from a cubic to a tetragonal phase was found in [(CH 3 ) 4 N] 2 PdCl 4 at 473K by DSC and polarization microscopy. A description of the phase transition consistent with the domain structure observed is presented.

Data are presented on dielectric properties of Rb2CoCl4 crystals. A wide tail of enhanced permittivity extends into the ferroelctric phase. It shows a relaxation in the MHz region with a wide distribution of relaxation times. On lowering temperature, the decrease in permittivity is accompanied by dielectric softening as revealed by decreasing mean relaxation frequency.

DSC measurements, polarizing microscopy and dielectric measurements on (NH4)2pdcl4 are presented. The existence of a phase transition at 149 K is proved unambiguously.

Two previously not known structural phase transitions in (CH3)4NCdBr3 are reported.

A logarithmically corrected Curie-Weiss law was the best fit of temperature dependence of relative permittivity measured in the paraelectric phase on 6 samples prepared from 4 high-quality TSCC crystals. It indicates, together with former results of Sandvold and Courtens, that a logarithmic correction describes an intrinsic property of TSCC crystals.

New relaxor ferroelectric system has been synthesized. BLTN exhibits a smeared maximum of permittivity, characteristic of classic relaxor behaviour, with a peak shift from 185 K at 100 Hz to 300 K at 1 GHz. BNTN undergoes a first order ferroelectric phase transition at 389 K and BLNTN exhibits both a ferroelectric phase transition at 274 K and relaxor behaviour at higher temperatures., Comment: subm. to J. Eur. Ceram. Soc., proceedings of Electroceramics IX conference, Cherbourg 2004

Thorough Raman and infrared (IR) reflectivity investigations of nominally pure ${\mathrm{SrTiO}}_{3}$ ceramics in the 10--300 K range have revealed a clear presence of the polar phase whose manifestation steeply increases on cooling. The Raman strengths of the Raman-forbidden IR modes are proportional to ${\ensuremath{\omega}}_{\mathrm{TO}1}^{\ensuremath{-}\ensuremath{\alpha}}(\ensuremath{\alpha}\ensuremath{\approx}1.6)$ where ${\ensuremath{\omega}}_{\mathrm{TO}1}$ is the polar soft mode frequency. No pronounced permittivity dispersion is observed below the soft mode frequency so that, as in single crystals, the static permittivity is essentially determined by the soft mode contribution. A theory is suggested which assumes a frozen dipole moment connected with the grain boundaries which induces the polar phase in the grain bulk in correlation with the bulk soft-mode frequency. This stiffens slightly the effective soft mode response and reduces the low-temperature permittivity compared to that of single crystals. Moreover, the polar soft mode strongly couples to the ${E}_{g}$ component of the structural soft doublet showing that the polar axis is perpendicular to the tetragonal axis below the structural transition which is shifted to 132 K in our ceramics. Whereas the ${\mathrm{TiO}}_{6}$ octahedra tilt (primary order parameter) below the structural transition corresponds to that in single crystals, much smaller ${A}_{1g}\ensuremath{-}{E}_{g}$ splitting of the structural soft doublet shows that the tetragonal deformation (secondary order parameter) is nearly 10 times smaller, apparently due to the grain volume clamping in ceramics.

We investigated ceramics samples of solid solutions of [PbFe(2/3)W(1/3)O(3)](x)-[PbZr(0.53)Ti(0.47)O(3)](1 - x) (PFW(x)-PZT(1 - x), x = 0.2 and 0.3) by means of broad-band dielectric spectroscopy, differential scanning calorimetry and SQUID magnetometry. We did not confirm the observations of Kumar et al (2009 J. Phys.: Condens. Matter 21 382204), who reported on reversible suppression of ferroelectric polarization in polycrystalline PFW(x)-PZT(1 - x) thin films for magnetic fields above 0.5 T. We did not observe any change of ferroelectric polarization with external magnetic fields up to 3.2 T. Pirc et al (2009 Phys. Rev. B 79 214114) developed a theory explaining the reported large magnetoelectric effect in PFW(x)-PZT(1 - x), taking into account relaxor magnetic and relaxor ferroelectric properties of the system. Our data revealed classical ferroelectric properties below 525 K and 485 K in samples with x = 0.2 and 0.3, respectively. Moreover, paramagnetic behavior was observed down to 4.5 K instead of previously reported relaxor magnetic behavior. It seems that the reported switching-off of ferroelectric polarization in PFW(x)-PZT(1 - x) thin films is not an intrinsic property, but probably an effect of electrodes, interlayers, grain boundaries or second phases presented in polycrystalline thin films.

We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Ram...

Dielectric spectra of two K0.5Na0.5NbO3 ceramics with different grain sizes (10 and 0.5 μm) were measured from 102 to 1014 Hz in a broad temperature range. The sequence of first-order phase transitions (cubic-tetragonal-orthorhombic-rhombohedral) was detected by differential scanning calorimetry, dielectric spectroscopy, and time-domain terahertz spectroscopy. The grain size affects all the phase transitions, which are more smeared in the small-grain sample. In the large-grain ceramics, two well-separated near-Debye relaxations are seen in the tetragonal phase, which suddenly merge on cooling across the tetragonal-orthorhombic transition, and on further cooling the lower-frequency relaxation strongly broadens. On reducing the grain size, the higher-frequency relaxation shifts from ∼1 to ∼20 GHz and the lower-frequency one strongly broadens. Without quantitative understanding, these effects could be assigned to domain-wall dynamics and its temperature and grain-size dependences. Similar to pure KNbO3, an o...

The polarized infrared reflectivity of incommensurate ferroelectric Rb2CoCl4 has been measured and evaluated in all crystal phases. Many sharp modes occur in the low temperature phase below 66 K in agreement with additional multiplication of the unit cell volume and lowering of the symmetry.

An improved technology of preparation of large Rb2CoCl4 single crystals is described. At the incommensurate-ferroelectric phase transition, the temperature hysteresis is only ∼ 4.1 K; near this transition, the permittivity value increases with increasing signal field strength. The paraelectric-incommensurate and ferroelectric-ferroelectric transitions are of the second order.

Growth striations have been studied in Fe-3wt%Si single crystals grown at various growth rates using floating zone melting with inductive heating. Well developed striations have been observed only in crystals grown at rates of 64 and 120 mm h -1 . In crystals grown at a rate of 21 mm h -1 only weak indistinct striations have been revealed. No striations have been observed in crystals grown at a rate of 7 mm h -1 . The striation structure has not been influenced by rotation of melted rod. It is suggested that unsteady surface tension-driven flow could be the dominant source of striations at floating zone melting. Some experiments indicate that the formation of striation is significantly suppressed at lower growth rates. Furthermore, solid-state diffusion of silicon could modify the striation structure during crystal growth, especially at lower growth rates.

The ferroelectric soft mode behaviour was studied in several SrTiO3 (ST)films on sapphire substrates using far infrared (FIR) transmission measurements and in the bulk ST ceramics using Raman and FIR reflectivity measurements down to 15 K. The recently established dramatic differences in softening and soft mode width compared to single crystal behaviour were confirmed in all the cases. Clear evidence of polar clusterappearance in the pure bulk ceramics indicates that the main reason for the observed differences in thin films are inhomogeneities due to the appearance of polar clusters or even a macroscopic ferroelectric transition at about 130 K in the case of well orientedinjection MOCVD film.

Raman and infra-red spectroscopic investigations of nominally pure SrTiO 3 ceramics have revealed a clear presence of polar phase whose manifestation steeply increases on cooling from room temperature. The Raman strengths of the Raman-forbidden infra-red modes are proportional to ω TO1 − α ( α ≈ 1.5) where ω TO1 is the polar soft mode frequency. Our explanation is based on an assumption of a temperature independent polarization P f fixed at grain boundaries. The effective polar soft mode is slightly shifted upwards at low temperatures, becomes broader and strongly coupled with the E g component of the structural soft mode which shows that P f is perpendicular to the tetragonal c -axis.

We have investigated the crystal structures of 186 polar molecular organic compounds with the aim to consider the occurrence of ferroelectric state. There are 16 crystals suspected of ferroelectricity. The results of tentative experimental investigations are also included.