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Ceramic lead niobates and their solid solutions (1 – x)Pb(Sc0:5Nb0:5)O3 – xPb(Yb0:5Nb0:5)O3 were synthesized by solid state reactions from oxides. The structure of investigated samples was characterized by X-ray diffraction (XRD). Dielectric studies of the ceramics were performed by means of broadband dielectric spectroscopy at the temperature ranging from 600 K to 140 K. For all ceramic samples a diffuse phase transition as well as relaxor ferroelectric behavior were observed. [ABSTRACT FROM AUTHOR]

The processes of low-frequency and infra-low-frequency polarization in solid solutions (1 ‒ х) Ba0.95Pb0.05TiO3 + хСо2О3 (x = 0; 0.1; 0.3; 0.5; 1; 2 wt %) prepared using conventional ceramic technology are studied at a wide range of temperatures. It is shown that adding cobalt (Co) substantially alters the thermal anomalies of the dielectric properties of samples and shifts the temperature of the ferroelectric phase transition. Data on the dielectric response in the samples are compared to the behavior of the elastic properties of ceramics at different contents of impurities. It is established that the disordering of the ceramic structure increases as Co is added. The domain component, which determines the main contribution from low-frequency polarization, is greatly reduced, and the nature of the dielectric non-linearity of the material is determined by inducing a macroscopic polar state from the microscopic state (the accumulation of polar nanodomains and phase boundaries). [ABSTRACT FROM AUTHOR]

Dielectric permittivity, dielectric losses and ac-conductivity of polycrystalline Bi1−xSmxFeO3 (x = 0; 0.05; 0.1; 0.15; 0.2) are measured in the frequency range 1 kHz–10 MHz and in the temperature range 25–600 °C. Anomalies have been observed at the 200 °C, 300 °C and at the Néel temperature. It has been demonstrated that doping with Sm has enhanced the dielectric properties and increased conduction in the frequency region <1 MHz. At high frequency (>1 MHz) and at a certain temperature Tm, depending on the composition Bi1−xSmxFeO3, the conductivity reaches a maximum. The results are discussed with reference to the model of correlated barrier hopping. [ABSTRACT FROM AUTHOR]

The ceramics of 0.95BaTiO3–0.05PbTiO3+Xwt.%CuO (X = 0.05, 0.1, 1, 3) were prepared by a solid phase reaction. The structural and morphology studies were carried out by means of X-ray diffraction technique (XRD) and scanning electron microscopy (SEM). It was found that CuO addition shifts two low-temperature transitions to higher temperatures. The increase of Cu ions concentration leads to a slight decrease of the Curie temperature. The enthalpy ΔH of the transition was estimated and discussed. Electrical properties of the sintered bodies were determined by electrical impedance spectroscopy (EIS) in temperature range 473–773 K. [ABSTRACT FROM AUTHOR]

The sintering conditions, phase structure, and electrical properties of the ZnO and CdO doped (Na0.5K0.5)NbO3 (NKN) ceramics were investigated and discussed. All the samples were prepared by a solid state reaction method. The addition of 1 wt% CdO and ZnO as a sintering aid increases the density and lowering the sintering temperature. XRD analysis indicated perovskite structure with monoclinic symmetry. The investigated samples are good quality, the grains are well shaped without a glassy phase. The results of dielectric measurements revealed, that the dielectric properties of NKN based ceramics are stable in the wide temperature range. [ABSTRACT FROM AUTHOR]

Ba0.7Pb0.3TiO3 and Ba0.7Pb0.3TiO3+yCuO (y = 0.1 wt%, 0.5 wt%, 1 wt% and 3 wt%) samples were prepared by a solid state reaction method. High purity raw materials were used. Structural properties of the sintered pellets were studied by X-ray diffractometer X'Pert PRO (PANalytical). A single phase of perovskite structure with tetragonal phase was identified at room temperature. The surface morphology of the obtained specimens was characterized by the scanning electron microscopy (Hitachi S4700). The investigations has shown that the synthesized ceramic materials are characterized by the high density, homogeneity of microstructure and low porosity. Dielectric spectroscopy was used to study the electrical properties of the solid solution on the basis of BaTiO3 doped CuO. [ABSTRACT FROM AUTHOR]

The paper presents the results of detailed studies of the thermal expansion of (1-x)PbNi1/3Nb2/3O3-xPbTiO3 solid solutions with x = 0-0.8. The anomalous and lattice contributions to deformation and the thermal expansion coefficient are analyzed and the mean square polarization Pd is determined. The results obtained are discussed within the framework of the thermodynamic theory and the Landau 2-4-6 coefficients for solid solutions are estimated. [ABSTRACT FROM AUTHOR]

A study of cobalt doping effect on the dielectric response and elastic properties of Ba0.95Pb0.05TiO3 solid solution within the range of 20–200 °C is reported. The results of a study of the dielectric permittivity, dielectric loss and elastic parameters in the samples of ceramic Ba0.95Pb0.05TiO3+xCo2O3 in the range of ferroelectric phase transition are presented. Modifying by admixture of Co is found to change the thermal anomalies of elastic and dielectric properties substantially, as well as to shift the ferroelectric phase transition temperature. [ABSTRACT FROM AUTHOR]

Properties of the dielectric response of (K0.5Na0.5)(Nb1 - xTax)O3 + 0.5 mol % MnO2 (KNN-xTa) ferroelectric ceramics at temperatures including that of the structural phase transition (SPT) from the orthorhombic phase to tetragonal is studied and compared to the behavior of elastic properties in this region of temperatures. The character is determined of the concentration dependences of such anomalies as the temperature of the maximum of permittivity Tmax(x) in the SPT region and temperature Textr at which the maximum increment of permittivity upon specimen heating in the SPT region occurs. It is found temperature Textr coincides with the one at which minimum v(T) of the velocity of a longitudinal acoustic wave is observed at SPT. Features of a nonlinear dielectric response associated with the coexistence of different types of domain boundaries in the region of a smeared structural transition in KNN-xTa ceramics are determined in studying the temperature behavior of polarization loops. [ABSTRACT FROM AUTHOR]

Copyright of Proceedings of the Estonian Academy of Sciences is the property of Teaduste Akadeemia Kirjastus and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Proceedings of the Estonian Academy of Sciences is the property of Teaduste Akadeemia Kirjastus and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Long-term changes of plant phenological phases determined by complex interactions of environmental factors are in the focus of recent climate impact research. There is a lack of studies on the comparison of biogeographical regions in Europe in terms of plant responses to climate. We examined the flowering phenology of plant species to identify the spatio-temporal patterns in their responses to environmental variables over the period 1970-2010. Data were collected from 12 countries along a 3000-km-long, North-South transect from northern to eastern Central Europe. Biogeographical regions of Europe were covered from Finland to Macedonia. Robust statistical methods were used to determine the most influential factors driving the changes of the beginning of flowering dates. Significant species-specific advancements in plant flowering onsets within the Continental (3 to 8.3 days), Alpine (2 to 3.8 days) and by highest magnitude in the Boreal biogeographical regions (2.2 to 9.6 days per decades) were found, while less pronounced responses were detected in the Pannonian and Mediterranean regions. While most of the other studies only use mean temperature in the models, we show that also the distribution of minimum and maximum temperatures are reasonable to consider as explanatory variable. Not just local (e.g. temperature) but large scale (e.g. North Atlantic Oscillation) climate factors, as well as altitude and latitude play significant role in the timing of flowering across biogeographical regions of Europe. Our analysis gave evidences that species show a delay in the timing of flowering with an increase in latitude (between the geographical coordinates of 40.9 and 67.9), and an advance with changing climate. The woody species (black locust and small-leaved lime) showed stronger advancements in their timing of flowering than the herbaceous species (dandelion, lily of the valley). In later decades (1991-2010), more pronounced phenological change was detected than during the earlier years (1970-1990), which indicates the increased influence of human induced higher spring temperatures in the late twentieth century. [ABSTRACT FROM AUTHOR]

Fe-doped BiMnO-BiMnO ceramics was sintered at 1130 K for 6 h in ambient air. Two centro-symmetric phases formed thermodynamically stable self-composite material that was deduced from X-ray pattern analysis. The lattice parameters were a = 10.147(8) Å-for the cubic I23 BiMnO phase; and a = 7.545(4) Å, b = 8.538(1) Å, c = 5.758(3) Å-for the orthorhombic Pbam BiMnO phase. The Fe Mössbauer spectrum, recorded at room temperature, has shown pure electronic quadrupolar split. The major doublets reflected the occurrence of Fe ions distributed in two sites, i.e., octahedral FeO and square pyramidal FeO, with preferential occupation of the pyramidal sites, that was consistent with the Pbam phase symmetry. The third doublet resulted from the presence of iron Fe in tetrahedral FeO coordination and corresponded to a small admixture of the I23 phase. The DC resistivity ρ ( T) dependence on temperature has shown thermally activated features, and the value of E varied in the range of 0.22-0.37 eV. The electric impedance was measured in the f = 20 Hz-1 MHz and 100-690 K range. Two electrical relaxations were determined using the electric modulus formalism M″( T). Low-temperature relaxation has shown the temperature-dependent activation energy E = 0.14-0.20 eV and characteristic time values of τ = 10-10 s in 100-200 K range. It was attributed to the charge transfer between Mn/Mn sites. The other relaxation occurred in the 170-220 K range, and it exhibited the following values: τ = 10 s, and E = 0.27 eV. A disorder-related VRH polaron model was proposed for ρ ( T) and for electric relaxation processes. [ABSTRACT FROM AUTHOR]

The paper deals with the hyperfine interactions observed on the57Fe nucleus in multiferroic BiFeO3by means of the 14.41-keV resonant transition in57Fe and for transmission geometry applied to the random powder sample. Spectra were obtained at 80 K, 190 K and at room temperature. It was found that iron occurs in the high-spin trivalent state. Hyperfine magnetic field follows distribution due to the elliptic-like distortion of the magnetic cycloid. The long axis of the ellipse is oriented along 〈1 1 1〉 direction of the rhombohedral unit cell. The hyperfine magnetic field in this direction is about 1.013 of the field in the perpendicular direction at room temperature. This ratio diminishes to 1.010 at 80 K. Axially symmetric electric field gradient (EFG) on the iron atoms has the principal axis oriented in the same direction and the main component of the EFG is positive. Our results are consistent with the finding that iron magnetic moments are confined to thecrystal plane. [ABSTRACT FROM PUBLISHER]

The crystal structure modifications of BaTiO3induced by cobalt doping were studied. The polycrystalline (1 −x)BaTiO3+xCo2O3samples, withx≤ 10 wt.%, were prepared by high temperature sintering conventional method. According to X-ray phase and structural characterization, performed by full-profile Rietveld refinement technique, all synthesized samples showed tetragonal symmetry perovskite structure with minor amount of parasitic phases. Pure single-phase composition has been detected only in the low level of doping BaTiO3. It was indicated that substitution of Co for the Ti sites in the (1 −x)BaTiO3+xCo2O3series led to decrease of tetragonality (c/a) of the BaTiO3perovskite structure. This effect almost vanished in the (1 −x)BaTiO3+xCo2O3samples with nominal Co content higher than ∼1 wt.%, in which precipitation of parasitic Co-containing phases CoO and Co2TiO4has been observed. Based on the results, the solubility limit of Co in Ti sub-lattice in the (1 −x)BaTiO3+xCo2O3series is estimated asx= 0.75 wt.%. [ABSTRACT FROM AUTHOR]

A study of the effects of ageing history on the electrical properties of lead-free ferroelectric ceramics of (K0.5Na0.5)(Nb1−xSbx)O3+ 0.5 mol% MnO2and (K0.5Na0.5)(Nb1−xTax)O3+ 0.5 mol%MnO2forx= 0.05 is reported. The samples after storage at a constant temperature have been subject to infra-low-frequency electric field and radiation. Differences of the photoelectric response between the two examined compounds were found and the restoration of polarisation in the aged ceramic materials by cycles of applied field is discussed. [ABSTRACT FROM AUTHOR]

The polycrystalline sample of BaTi0.95Ge0.05O3was prepared by solid-phase reaction using a conventional method. The morphology of investigated sample was characterised by scanning electron microscopy (SEM). The results allowed to determining the stoichiometry of the material and evaluate their microstructure. High quality samples were investigated, the grains are well shaped without of a glassy phase. The dielectric properties of the BaTi0.95Ge0.05O3ceramics were determined. The results were compared with these ones obtained for pure BaTiO3. The obtained data indicated that the substitution of Ge+4ions had an influence on the values of the real (ϵ′) and imaginary (ϵ″) parts of electric permittivity. [ABSTRACT FROM PUBLISHER]

Lead-free (Na0.5Bi0.5)1−xSrxTiO3(x= 0, 0.04 and 0.06) ceramics with relative densities above 97% were prepared by solid-state synthesis process. Their dielectric, thermal and Raman properties were studied. X-ray diffraction analysis shows perovskite structure with rhombohedral symmetry at room temperature. Sr doping of Na0.5Bi0.5TiO3(NBT) results in an increase of the dielectric permittivity, diffusing of the permittivity maximum and its shift toward lower temperatures. The temperature of the rhombohedral–tetragonal phase transition indicated by the differential scanning calorimetry (DSC) peak and relaxational dielectric anomaly near the depolarization temperature are also shifted toward lower temperatures. The observed increase and broadening of the permittivity maximum, enhancement of the dielectric relaxation near the depolarization temperature, broadening of the DSC anomaly related to the rhombohedral–tetragonal phase transition and broadening of the Raman bands with increasing Sr content are attributed to the increase of the degree of cationic disorder and evident enhancement of the relaxor-like features in NBT–xST. This enhancement could play a positive role in the improvement of the piezoelectric performance of NBT-based ceramics. [ABSTRACT FROM AUTHOR]

SrMnO3ceramic was prepared by conventional high-temperature sintering method. Dielectric studies were performed within the temperature range 125–300 K at the frequency 10–400 kHz. The electronic properties of stoichiometric and oxygen defected SrMnO3crystal in hexagonal 6H- P63/mmc symmetry at 0 K were calculated inab initioprocedure based on density functional theory using the Spanish Initiative for Electronic Simulations with Thousands of Atoms (SIESTA) code. The lattice parameters and density of states were obtained. The ideal 6H-SrMnO3crystal has the band gap energy about 0.2–0.3 eV at 0 K. Contribution of an exchange-correlation energy into the total energy is about 32%, a magnetic moment about 3 µB. [ABSTRACT FROM AUTHOR]

The external stress (0–1500 bar) dependence of dielectric properties and an aging effect of BiFeO3ceramic has been investigated. The electric permittivity and dielectric losses first increased (up to about 700 bar) and next decreased with uniaxial pressure applied parallel to the ac field direction, while increased with the stress perpendicularly applied. It was suggested that combination of the de-aging, clamping of the domain walls, and the polarization reorientation mechanisms can be responsible for these changes. The aging effect is followed logarithmic law and is related to the relaxation of the domain structure towards an equilibrium configuration. [ABSTRACT FROM AUTHOR]

The barium titanate (BaTiO3) and the BaTiO3+ 0.1wt.% Eu2O3ceramics were prepared by a conventional ceramic method. The structural studies were carried out by means of an X-ray diffraction technique. The influence of the grains and the grain boundaries on the electrical properties was investigated using a impedance spectroscopy. This technique enables us to determine the values of grain and grain boundary resistance. The results show that the Eu doping leads to a significant reduction in the resistance value of the grains (˜105Ω) with respect to the pure BT ceramics (˜107Ω). The conductivity processes were determined from the Arrhenius behaviour of grain and grain boundary resistances. [ABSTRACT FROM AUTHOR]

The Ba1−xSrxTiO3(BST) ceramics were prepared by conventional ceramic method. The crystalline structure and morphology were studied by X-ray diffraction and scanning electron microscopy, respectively. Experimental results show that increase of sintering temperature leads to an uncontrolled precipitating of the phase with a lower content of Ti. The dielectric constant and specific heat as a function of composition and temperature were investigated. The increasing concentration of Sr ions leads to a shift of the Curie point below room temperature. To determine the elastic constants (the Young's modulus E, the shear modulus G and the Poisson's ratiov) of BST, a method of measurement of the longitudinal (νL) and transverse (νT) ultrasonic wave velocities for this type of material was developed. The structural, dielectric and mechanical properties of BST ceramics were discussed in terms of microstructure and chemical composition [ABSTRACT FROM AUTHOR]

The impedance spectrum of hexagonal SrMnO3, rhombohedral BaMnO3and orthorhombic Ba0.5Sr0.5MnO3ceramics, synthesized by conventional high-temperature method, was studied in a wide temperature and frequency range. The complex impedance plots ofZ″ versusZ′ pointed to two contributions originating from grains and grain boundaries. The parameters of electric equivalent circuit were calculated. The semicircles related to the grain boundary are located at the lower frequency side due to higher resistivity and capacity of the grain boundaries. The Ba0.5Sr0.5MnO3ceramics is characterized by the lowest activation energy related to the grains. The conductivities σacof all the investigated samples show plateaus being a characteristic of the dc conductivity. The conductivity of Ba0.5Sr0.5MnO3takes the values between those of BaMnO3and SrMnO3. [ABSTRACT FROM AUTHOR]

A study of dielectric response to weak and strong measuring fields at temperatures of the diffuse phase transition in lead-magnesium niobate—lead-nickel niobate (PMN-PNN) containing an admixture of lithium is reported. A relaxor behaviour of the ceramic compound manifesting itself by a substantial shift of the temperature of dielectric permittivity maximum with field intensity and frequency is detected. Specific features of the dielectric nonlinearity observed at temperatures considerably higher than the temperature of the low-frequency dielectric permittivity maximum are related to extension of the range of phase transition to higher temperatures. This extension is related to formation of nano-size polar clusters within the region of the diffuse phase transition, the cluster formation being substantially affected by the applied field. [ABSTRACT FROM PUBLISHER]

Dielectric response of BaPbTiO ceramics doped with 0.1 and 1 wt.% of CoO, synthesized by conventional high-temperature method, was studied in wide temperature and frequency range. The temperature dependences of the real and the imaginary parts of dielectric permittivity of the ceramics were compared with those of BaTiO and BaPbTiO The addition of Co ions results in a broadening of dielectric anomalies related to the transition to paraelectric cubic phase, and the structural transition between the tetragonal and the orthorhombic phases. At low temperatures (125-200 K) the dielectric absorption of Co-doped BaPbTiO ceramics was found to exhibit relaxor-like properties. The dielectric response has been found to contain the contributions characteristic of fluctuations of the polar nanoregion boundaries and reorientations of the dipole moments between allowed directions in the nanoregions in the rhombohedral and the orthorhombic phases. The behavior speaks in favor of ordering of polar defects in the host lattice of BaPbTiO in a form polar nanoregions [ABSTRACT FROM AUTHOR]

Ferroelectric properties of BaTi1−xHfxO3ceramics with Hf contentx = 0, 0.001, and 0.025 were examined. It was found that the substitution of Hf4+for Ti4+in BaTiO3resulted in shifting the two low-temperature transitions (T1,T2) of the investigated samples to higher temperatures and decreasing the tetragonal-cubic phase transition temperature (Tc). This is a well-known pinching effect. Thermal parameters of the transitions, such as the enthalpy ΔHand the entropy ΔS, were also estimated and discussed. [ABSTRACT FROM AUTHOR]

A study of heat capacity as function of temperature of the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3solid solution within the 120–800 K range is reported. Broad anomalies on the curve of heat capacity are revealed in the 250–450 K and 450–650 K intervals peaking at 520 K and aλ-anomaly atT ≈ 225 K. Results are discussed with account for dielectric and structural data. [ABSTRACT FROM AUTHOR]

The reported study is focused on effects of relaxation of polarization within the range of the broad phase transition at strong sinusoidal measuring fields in modified lead magnesium niobate ceramics. The obtained results reveal an essential thermal broadening of the ϵ′(E)spectra specific to relaxor ferroelectrics. Temperature dependence of ϵ′eff(T)at medium fields shows two broad maximums – atTmand at 40°C. On the basis of analysis of the experimental data, admixture of lithium is suggested to promote formation of domains in lead magnesium niobate ceramics. [ABSTRACT FROM AUTHOR]

We have investigated dielectric and acoustic properties of PbFe1/2Nb1/2O3ceramics, obtained by conventional ceramic technology, in 120–450 K temperature interval. Dielectric response showed diffused dielectric permittivity maximum caused by ferroelectric phase transition around 380 K, but no dielectric anomalies associated with magnetic phase transition at low temperatures were observed. Formation of the polar phase was confirmed by ultrasonically detected piezoelectric sensitivity. Ultrasonic investigations using pulse-echo method showed two anomalous regions in temperature dependencies of ultrasonic velocity and attenuation, associated with magnetic and ferroelectric phase transitions. [ABSTRACT FROM AUTHOR]

This paper presents results of new far-infrared and middle-infrared measurements (wavenumber range of 4000-100 cm) of the CoFeO ceramic in the temperature range from 300 K to 8 K. The band positions and their shapes remain constant across the wide temperature range. The quality of the sample was investigated by X-ray, EDS and EPMA studies. The CoFeO retains the cubic structure ( Fd - 3 m) across the temperature range from 85 K to 360 K without any traces of distortion. Based on current knowledge the polycrystalline CoFeO does not exhibit any phase transitions across the temperature range from 8 K to 300 K. [ABSTRACT FROM AUTHOR]

A study of dielectric permittivity and heat capacity of the (1-х)PbNi1/3Nb2/3O3– хPbTiO3solid solution system (x = 0.3, 0.4, 0.5) within the 290–700 K range is reported. Temperatures of phase transitions Tmdetermined from maximums of dielectric permittivity ϵ depends on the content of PbTiO3. A broad phase transition is shown to proceed in the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3composition around 312 K. Specific to phase transitions anomalous heat capacity is observed at Т ≈ 520 K in all compositions studied. [ABSTRACT FROM AUTHOR]

The single-phase perovskite structure of the Ba0.95Pb0.05TiO3+0.1%Co2O3ceramics was confirmed by the X-ray diffraction method. Microstructural studies revealed that the samples were of good quality and chemically homogeneous. The thermal behaviour of ceramics was studied using thein situhigh-temperature X-ray synchrotron powder diffraction investigation. The energy gap of about 3.2 eV was estimated using a reflectance spectroscopy. Measurements showed the influence of Pb and Co on the character of phase transition in the BaTiO3structure. The results were compared to the ones obtained for pure BaTiO3. [ABSTRACT FROM AUTHOR]

The dielectric response of 0.98Pb(TiZr)O-0.02Bi(SrTi)O ceramics is studied over a wide temperature range at various ac and bias fields. Anomalies are detected in the behavior of the dielectric nonlinearity in the temperature range 90-160°C, which is well below the Curie temperature. These anomalies are found to be related to the existence of a diffuse structural phase transition in the ceramics. [ABSTRACT FROM AUTHOR]

The influence of Zr doping on a structure and dielectric properties of Ba0.8Sr0.2TiO3 were studied. For this purpose Ba0.8Sr0.2Ti0.75Zr0.25O3 ceramics were obtained by a conventional method and were determined by an X-ray diffraction (XRD) and scanning electron microscopy (SEM) for crystallographic, surface morphological and compositional studies. The temperature and frequency dependence of dielectric permittivity were studied in the temperature range from 150 to 500 K and the frequency between 20 Hz and 1000000 Hz. The thermal behavior of the Ba0.8Sr0.2Ti0.75Zr0.25O3 ceramics were also studied using Differential Scanning Calorimetry. A diffusivity coefficient γ was calculated. [ABSTRACT FROM PUBLISHER]

A lead-free solid solution Li0.08Na0.92NbO3 was prepared by a two-stage hot-pressing technology. The structure and morphology of Li0.08Na0.92NbO3 were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The studies of electric conductivity were performed depending on temperature and frequency of electric measuring field on heating and cooling processes. These measurements revealed that the a.c. conductivity changed with the frequency according to the formula: σ(ω)=σ dc +Aω n where n < 1. These results were discussed considering the conduction mechanism as a type of polaron hopping. [ABSTRACT FROM PUBLISHER]

In this paper, results of new infrared FIR-MIR measurements (wavenumber range of 4000–100 cm−1) in the range of the temperature 300 ÷ 8 K of the BiFeO3 ceramic are presented. Below 200 K only one symmetric band at ca. 800 cm−1 is visible. The full width at half maximum of this band decreases exponentially on cooling. The shape of the band at ca. 545 cm−1connected with A1 (TO) mode also changes between 60–40 K, this is in the vicinity of the phase transition at 50 K. Initially a broad band reveals its components as shoulder bands. Theirs FWHM decrease with cooling. [ABSTRACT FROM PUBLISHER]

Dielectric properties of Sr0.75Ba0.25Nb2O6 (SBN-75) ceramics in the range of low and infra-low frequencies are reported. The values of ϵ′ and, in particular of ϵ″, in ceramics are found to be much smaller compared with SBN-75 single crystals below the temperature (Тm) of the ϵ′(T) maximum a sharp increase of the values of dielectric parameters observed above Тm being also different from their thermal behaviour in single crystals. The broadening of phase transition and dependence of the response on sample history are similar to the features observed in other relaxor materials. [ABSTRACT FROM PUBLISHER]

In the paper the influence of zirconium admixture on the structure and material constants of polycrystalline ferroelectric materials BaZrxTi1-xO3 (BZT) was examined. The barium zirconate titanate samples were prepared by a conventional solid state reaction method. A single phase with perovskite structure of the samples, was identified by an X-Ray diffraction technique at room temperature. The performed EDS study revealed that the samples were perfectly sintered and the material was chemically homogeneous. The dependence of shear modulus G on sample composition is similar to the respective dependence of Young's modulus E, whereas the Poisson's ratio ν decreases with the increase in zirconium concentration. [ABSTRACT FROM AUTHOR]

Studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics at low- and infra-low-frequencies under bias field over a wide range of temperatures are reported. Applied bias field is found to broaden the ε'(Т) maxima shifting positions Тm of the maximums to higher temperatures. Additional anomalies in the dielectric response are revealed at T<Тm. The anomalies in the vicinity of Тm are related to structural change at phase transition, while those observed at T[image omitted]Тm - to magneto-electric interactions in PbFe1/2Ta1/2O3. [ABSTRACT FROM AUTHOR]

Lead-free ceramics of Na0.5Bi0.5TiO3–Ba(Ti,Zr)O3 (NBT–BTZ) were prepared by solid phase hot pressing sintering process. The obtained samples show perovskite structure. Structural, the heat capacity, thermal expansion and pyroelectric measurements were made in wide temperature range. The broad anomalies of heat capacity and thermal expansion were observed, which approximately correspond to structural, pyroelectric and dielectric properties. It was concluded that these anomalies can be connected with temperature features of polar regions and with formation of long-range ferroelectric state. The obtained results are discussed in the framework of foreign ions/lattice imperfections, which create local electric and elastic fields. The NBT–BTZ system is expected to be a new promising candidate for lead-free electronic ceramics. [ABSTRACT FROM AUTHOR]

Microstructure and material constants such as Young modulus E, shear modulus G, Poisson ratioν of polycrystalline ferroelectric materials Ba1-xSrxTiO3 for 0≤x≤0.4 were investigated to determine their dependence on strontium concentration. The performed investigations showed that the material is chemically homogeneous. It was found that the strontium concentration had no significant influence on the grain size. The highest value of Young's modulus is observed for Ba0.6Sr0.4TiO3 sample. The performed investigations of mechanical properties made it possible to evaluate the usability of this material for manufacturing transducers and sensors which could work under load. [ABSTRACT FROM AUTHOR]

Lead-free BaZrxTi1-xO3 (x = 0; 0.025; 0.125) ceramics have been obtained by a conventional method. A single-phase perovskite structure of the ceramics was identified by the X-ray diffraction method. EDS analysis, performed for the individual grains of the tested sample, showed a good homogeneous distribution of all elements throughout the grains. The thermal behaviour of BaZrxTi1-xO3 (x = 0; 0.025; 0.125) ceramics was studied using the Differential Scanning Calorimetry (DSC). Measurements showed the influence of Zr addition on the character of phase transition in the BaTiO3 structure. The results were compared with these ones obtained for pure BaTiO3. [ABSTRACT FROM AUTHOR]

Perovskite structures with high dielectric constants and magnetic properties play an important role in micro- and optoelectronics and have numerous practical applications. Relaxor type ferroelectric ceramics PbFe1/2Ta1/2O3 with perovskite structure was subject of present studies. Pyrochlore free lead ferrotantalate ceramics were produced by solid state technology from oxides. Low- and infra-low frequency studies of dielectric properties of PbFe1/2Ta1/2O3 ceramics have revealed considerable infra-low frequency dispersion at temperatures above the temperature of maximum dielectric permittivity. The observed dispersion described by lemniscates is due to a considerable Maxwell-Wagner relaxation. [ABSTRACT FROM AUTHOR]

The sodium niobate-lithium niobate (LixNa1 - xNbO3) compounds were synthesized using conventional solid-state processing. Phase analysis was performed by X-Ray diffraction, and microstructural morphology was assessed by scanning electron microscopy. The dielectric measurements were performed in heating and cooling processes without and under axial pressure up to 120 MPa. It has been stated, that the maximum of electric permittivity ε (T) becomes more diffused with the increase of axial pressure and the temperature of phase transition T0 decreases. The value of tanδ increases with the increase of axial pressure and its local maximum shifts towards lower temperatures. [ABSTRACT FROM AUTHOR]

Lead-free ceramics based on (Na0.5Bi0.5TiO3, NBT)-(Ba(Ti,Zr)O3, BTZ) were prepared by solid phase hot pressing sintering process and their ac (σac) and dc (σdc) conductivity have been studied (303-753 K). Low frequency (100 Hz-100 kHz) ac conductivity obeys power law σac∼ ωs characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σac (T) possesses two linear parts with two different activation energies and more discontinuous changes than dc conductivity. The results was interpreted by correlated hopping model. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics. [ABSTRACT FROM AUTHOR]