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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.

The data of the title structure of 2,4,6-triaminopyrimidinium(1+) x hydrogen trioxofluorophosphate(1−) x monohydrate/2,4,6-triaminopyrimidinium(2+)1−x trioxofluorophosphate(2−)1−x monohydrate (0.0 < x < 0.73), with the sum formula C4H11FN5O4P, were collected in 10 K intervals between 290 and 150 K, as well as at 100 K. The most interesting feature is the presence of a moderate though still strong O—H...N/O...H—N hydrogen bond. Its bridging H atom was found to be disordered over two positions in the temperature interval 290–220 K, with the larger occupation towards the O atom. The occupation in the latter position decreased with decreasing temperature, though not monotonously. At 210 K and below, the difference electron-density maps showed just one maximum which was closer to the N atom. Though difference scanning calorimetry (DSC) revealed no anomaly in the interval 303–93 K, the dependence of the length of the unit-cell axes b and c on temperature showed a kink in the slope at about 190 K. The N...O distance of the mentioned hydrogen bond or the occupational parameter of the electron density of the disordered H atom indicate less pronounced anomalies for the temperatures 270 and 230 K. The cation and the anion, as well as the water molecules, form layers which are parallel to (10\overline{1}) and which are interconnected by O—H...N (in the interval 290–220 K), N—H...O and O—H...O hydrogen bonds of moderate strength. The layers are arranged into centrosymmetric double layers in which the F atoms are directed outwards. The layers are interconnected by water–acid O—H...O hydrogen bonds, weak N—H...F interactions and π-electron ring...π-electron ring interactions. The dependence of P—F bond lengths on bonding properties of the trioxofluorophosphate or hydrogen trioxofluorophosphate anions is discussed. It has been recognized that a carbon-bonded F atom avoids participation in a hydrogen-bond pattern; however, this property seems to be also common to fluorine bonded to P, As and S, especially if an oxygen ligand is also present in a molecule. The deposited material contains an overview of the determined structures with trioxofluorophosphate or hydrogen trioxofluorophosphate anions.

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)].

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...

Aminoguanidinium(1+) dihydrogen phosphate was prepared by crystallization from aqueous solution. On the basis of the results of DSC measurements, X-ray structural analysis was carried out at temperatures of 160, 215 and 293 K for three aminoguanidinium(1+) dihydrogen phosphate phases ( I | > 222 K | P 1 ¯ ( 2 ) |Z=2|non-ferroic |melting point 408 K; II |201–222 K| P 1 ¯ (2) |Z=2|non-ferroic|-; III | P 1 ¯ (2)|Z=4|non-ferroic|-). The triclinic unit cell dimensions (a=6.8220(2), b=7.1000(2), c=7.4500(2) A, α = 86 .925(2)°, β = 80 .731(2)°, γ = 79 .630(2)°, V = 350 .21(2) A3—phase I) are similar for all three structural phases with the exception of phase III, where doubling of the c-axis length leads to an increase in the volume to 692.34(3) A3. The crystal structure of all three modifications consists of parallel layers of dihydrogen phosphate anions that are interconnected by aminoguanidinium(1+) cations through hydrogen bonds of the N–H…O type. The planar aminoguanidinium(1+) cations are oriented almost parallel to each other and are perpendicular to the anion layers. The primary differences amongst phases I, II and III lie in the location of the H atom in the short O–H…O bonds connecting the dihydrogen phosphate anions in layers. The FTIR and FT Raman spectra of natural and deuterated compounds were recorded and interpreted. The FTIR spectra were studied down to a temperature of 90 K.

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.

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.

Infrared reflectivity spectra of cubic SrMnO$_{3}$ ceramics reveal 18 % stiffening of the lowest-frequency phonon below the antiferromagnetic phase transition occurring at T$_{N}$ = 233 K. Such a large temperature change of the polar phonon frequency is extraordinary and we attribute it to an exceptionally strong spin-phonon coupling in this material. This is consistent with our prediction from first principles calculations. Moreover, polar phonons become Raman active below T$_{N}$, although their activation is forbidden by symmetry in $Pm\bar{3}m$ space group. This gives evidence that the cubic $Pm\bar{3}m$ symmetry is locally broken below T$_{N}$ due to a strong magnetoelectric coupling. Multiphonon and multimagnon scattering is also observed in Raman spectra. Microwave and THz permittivity is strongly influenced by hopping electronic conductivity, which is caused by small non-stoichiometry of the sample. Thermoelectric measurements show room-temperature concentration of free carriers $n_{e}=$3.6 10$^{20}$ cm$^{-3}$ and the sample composition Sr$^{2+}$Mn$_{0.98}^{4+}$Mn$_{0.02}^{3+}$O$_{2.99}^{2-}$. The conductivity exhibits very unusual temperature behavior: THz conductivity increases on cooling, while the static conductivity markedly decreases on cooling. We attribute this to different conductivity of the ceramic grains and grain boundaries., Comment: subm. to PRB

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.

Polarized far-infrared reflectivity and Raman scattering spectra of LiNaGe 4 O 9 single crystals were studied between 15 and 300 K. Even if the ferroelectric phase transition in this material is of order-disorder type and critical relaxation was estimated from our data in the region 0.13 to 13 cm -1 , pronounced phonon softening in four different symmetry spectra was observed near T c . This indicates changes in interatomic bonds caused by local Li and Na atom ordering and accompanying shifts of GeO polyhedra even above T c . Phonon anomalies observed about 45 K below T c in the E ∥ a far-infrared spectra might suggest another phase transition, but no corresponding dielectric anomaly was observed in previous dielectric measurements.

One of the purposes of this work is to provide a crystallographic review of group 1 and thallium rare-earth ternary sulfidesM+Ln3+S2. We have therefore determined crystal structures of KLaS2, KPrS2, KEuS2, KGdS2, KLuS2, KYS2, RbYS2, which belong to the α-NaFeO2structural family (R \bar 3 m), as well as NaLaS2, which is derived from the disordered NaCl structural type (Fm \bar 3 m). The determined structures were compared with known members of the group 1 as well as thallium(I) rare-earth sulfides by the standard tools of crystal-chemical analysis such as comparison of bond-valences, analysis of interatomic distances and comparison of the unit-cell parameters. The results indicate why the cubic structural type is limited to Li+and Na+members of the series only. The analysis has also revealed frequent problems in the reported crystal structures, especially in the determination of the K+compounds, probably due to severe absorption and different accuracy and sensitivity of various instruments. Intense diffuse scattering has been discovered in NaLaS2, which will be the subject of further investigation. The newly determined as well as already known structures are summarized, together with critical comments about possible errors in the previous structure determinations.

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.

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.

Fourteen new structural phase transitions are detected in layer-type monoalkylammonium hexachloro-stannates (CnH2n+1NH3)2SnCl6 (n = 2 to 8) by means of differential scanning calorimetry. The basic thermodynamic data are determined for the transitions. The infrared spectra of the compounds are measured in the range of molecular vibrations (500 to 4000 cm−1) at room temperature and in dependence on temperature (77 to 298 K) by the method of nujol mull. Vierzehn neue strukturelle Phasenumwandlungen werden in geschichteten Monoalkylammonium-hexachlorostannaten (CnH2n+1NH3)2SnCl6 (n = 2 bis 8) mittels dynamischer Leistungs-Differenzkalorimetrie entdeckt. Es werden die thermodynamischen Grunddaten fur diese Umwandlungen ermittelt. Die Infrarotspektren dieser Verbindungen werden im Bereich der Molekulschwingungen (500 bis 4000 cm−1) bei Raumtemperatur und in Abhangigkeit von der Temperatur (77 bis 298 K.) mit Hilfe einer Nujolsuspension gemessen.

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.

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.

Raman spectra of Rb2CoCl4 (RCC) single crystals, prepared by an improved method, are studied at 90 to 297 K. The results show that the temperature dependence of the spectra of RCC is analogous to that of Rb2ZnCl4 and Rb2ZnBr4. Eigenfrequencies of internal modes v1 and v3 vary with temperature in a manner well describable by a model, which is suggested by Rasing et al. for Rb2ZnBr4. Low-frequency lines at 20 and 37 cm−1 exhibit a pronounced temperature dependence. The broadness of spectral lines speaks for a high anharmonicity of oscillations in RCC. Zwischen 90 bis 297 K werden die Ramanspektren von Rb2CoCl4 (RCC)-Einkristallen, hergestellt nach einer verbesserten Methode, untersucht. Die Ergebnisse zeigen, das die Temperaturabhangigkeit von RCC zu dem von Rb2ZnCl4 und Rb2ZnBr4 analog ist. Die Eigenfrequenzen der inneren Moden v1 und v3 variieren mit der Temperatur in einer Weise, die gut durch ein von Rasing et al. fur Rb2ZnBr4 vorgeschlagenes Modell erklart werden kann. Die Niederfrequenzlinien bei 20 und 37 cm−1 zeigen eine ausgepragte Temperaturabhangigkeit. Die grose Breite der Spektrallinien weist auf eine hohe Anharmonizitat der Oszillationen in RCC hin.

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.

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.

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.