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The current study demonstrates the effect of Ni-substitution on the structural, dielectric and ferroelectric properties of Ba0.90Sr0.10Ti1-xNixO3 (where x = 0.000, 0.005, 0.015 and 0.025) ceramics, synthesized by solid-state reaction approach. A pure perovskite phase with tetragonal structure has been confirmed by X-ray diffraction (XRD) analysis. Scanning electron microscope (SEM) images revealed change in microstructure. The dielectric behavior of the prepared ceramics was investigated as a function of temperature (30–150°C) at different frequencies. The results indicate that there is an increase in dielectric constant (ϵRT) and low dielectric loss (tanδRT) were obtained at room temperature by substitution of Ni2+ ions in BST ceramics, offering a promising material for capacitor applications at room temperature. Room temperature P-E loops were recorded at different applied electric fields and typical hysteresis loops were obtained. Improvement in the values of Pr and Pmax was observed by substitution of Ni2+ ions. [ABSTRACT FROM AUTHOR]

The standard solid state reaction method was followed to synthesize the polycrystalline xBa0.95Sr0.05TiO3-(1-x)BiFe0.9Sm0.1O3 [xBST-(1-x)BFSmO, x = 0-0.35] ceramics. The XRD pattern revealed a structural transition of the prepared ceramics from rhombohedral to cubic symmetry. The mean grain size was estimated in the micrometer range, with values ranging from 0.40 to 1.95 μm. The maximum real part of the complex initial permeability of 28.26 was noticed for x = 0.30 multiferroic ceramics. The highest remanent magnetization determined for the x = 0.30 sample was 3.4 10-2 emu/g. For the sample with x = 0.35 the maximum recorded dielectric constant was found to be 677 at 103 Hz. A small value of dielectric loss (<5%) was observed. The compound exhibited significant remanent polarization and a reduction in the leakage current. In addition, the investigated materials comprise large magnetoelectric coefficients and the optimum magnetoelectric coefficient of 0.662 mV.cm-1.Oe-1was obtained for the x = 0.30 composition. [ABSTRACT FROM AUTHOR]

The (Na0.47Bi0.47Ba0.06)0.99Ca0.01TiO3 lead-free ferroelectric ceramics were prepared via the conventional solid-state reaction method. The atmospheres of nitrogen and oxygen were chosen during the sintering process, respectively. Both the ceramics sintered in nitrogen and oxygen atmospheres exhibit high relative density (>96%) and pure perovskite structure. The dielectric behaviors with diffusion phase transition were studied via the Curie–Weiss law and the modified Curie–Weiss law. The piezoelectric and ferroelectric properties of the two kinds of ceramics were studied comparatively. Compared to the O2 fired ceramics, the N2 fired samples exhibit higher depolarization temperature (Td= 117°C). The O2 fired ceramics show higher piezoelectric constant (d33 = 113 pC/N) and higher polarization values (Pm = 40.4 μC/cm2, Pr = 34.4 μC/cm2). The differences in the electrical properties of the ceramics sintered in the different atmospheres were discussed. [ABSTRACT FROM AUTHOR]

A Landau-Ginzburg-Devonshire(LGD) theory based on a structurally stable 8th-order potential with three varying expansion coefficients (a1, a11 and a2) was proposed for phenomenological description for KNbO3. The phase diagrams in the space of phenomenological parameters of the LGD potential model with co-dimension (Codim) of 2 and 3, invariant under the cubic point group m3m, were constructed. The values of the phenomenological coefficients of the potential model were determined by fitting experimental data. The theoretical pressure-temperature phase diagram which can explain the experimentally observed cubic-tetragonal-orthorhombic triple point and cubic-orthorhombic phase transition was constructed. Temperature dependences of spontaneous strain, lattice constants, dielectric constants and spontaneous polarization calculated with this potential model were in good agreement with the experimental data. Furthermore, the influence of the hydrostatic pressure on the dielectric constant (ε33) in the vicinity of the triple point and the dependence of piezoelectric coefficients on the applied electric field were predicted. [ABSTRACT FROM AUTHOR]

Na0.5Bi0.5TiO3ceramics were prepared by a conventional solid-state reaction method and by a hot-pressing route. The influence of sintering conditions on structural, thermal, dielectric and ferroelectric properties of these ceramics was investigated. All obtained samples exhibited a single perovskite phase. It was shown that the sintering conditions significantly influence the properties under investigation. This includes changes in the value of the electric permittivity ϵ and dielectric loss tanδ, a shift ofTmandTdand change of the ferroelectric properties. These effects are mainly related to volatility of the Na and Bi components during the sintering process along with formation of their compensating charge defects, which leads to local structure change. [ABSTRACT FROM AUTHOR]

The (1-x)Na0.5Bi0.5TiO3-xBaTiO3ceramics (x= 0.1, 0.135 and 0.17) were fabricated by a conventional solid phase sintering process. The bulk density of the obtained samples exceeded 95% of the theoretical relative density as determined by Archimedes method. Dielectric and ferroelectric measurements of these ceramics were performed. Measurements of the ferroelectric properties show that, above the depolarization temperature Td, the shape of the hysteresis loops approaches that of linear dielectrics. The dielectric study results correlate with the hysteresis loops measurements. The relaxor-like behavior of the investigated materials was revealed. [ABSTRACT FROM AUTHOR]

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]

High-quality, large-size lead-free (1 –x)Na0.5Bi0.5TiO3–xBaTiO3((1 –x)NBT–xBT) single crystals (x= 0, 0.025, 0.0325 and 0.05) were grown using the Czochralski method. Dielectric and transmitted light intensity properties were measured for these crystals. The broad anomalies exhibited in the temperature dependence of the transmitted light corresponded to structural and dielectric anomalies and were related to the temperature dependence of polar regions and the appearance of a long-range ferroelectric state. We explain our results based on local electromechanical fields, by inhomogeneity of the ion distribution and the mismatch in ion size. We suggested that the NBT–BT system can be a promising lead-free piezoelectric material for ultrasonic delay-line applications, broadband transducers and sensors. [ABSTRACT FROM PUBLISHER]

New low-lead content 0.925BaTiO3–0.075PbZn1/3Nb2/3O3(0.925BT–0.075PZN) ceramic was fabricated by the spark-plasma-sintering method. X-ray diffraction measurements showed that the obtained specimen possesses a pure perovskite structure. The microstructure investigation indicated a dense ceramic structure with 95% relative density determined by the Archimedes method. Composition undergoes a sequence of phase transitions as pure barium titanate (BT). Dielectric study revealed that the electric permittivity decreases at its maximum and the phase transition shifts to a higher temperature after lead zinc niobate doping of BT. Besides, the dielectric dispersion and polarization increases and decreases, respectively. Obtained results were discussed in term of the difference between ionic size and its mass and local elastic and electric fields. The results show that investigated ceramic is one of the promising low-lead materials for electronic applications. [ABSTRACT FROM AUTHOR]

0.82K0.5Bi0.5TiO3-0.18PbTiO3ceramic was fabricated by the mixed oxide method. An X-ray study shows that the obtained ceramic has a pure perovskite structure. The ϵ(T) and tanδ(T) show a peak centered at about 468 °C and 421 °C, respectively, and related to the tetragonal–cubic phase transition. The effect of uniaxial pressure (0–1500 bar) on dielectric and ferroelectric behavior of this ceramic was investigated. It was shown that uniaxial pressure significantly influences these properties. With the increasing pressure, (1) the maximum value of the electric permittivity and dielectric losses tanδ decreases and increases, respectively, (2) the peaks of ϵ and tanδ shift to higher temperatures, (3) the permittivity characteristics are smeared and the thermal hysteresis decreases, (4) hysteresis loops are smeared. The results were interpreted in term of domains (domains walls) change and de-aging process under the action of uniaxial pressure. [ABSTRACT FROM AUTHOR]

Lead-free Na0.5K0.5NbO3and Na0.5K0.5NbO3+0.5mol%MnO2ceramics were fabricated by solid state hot pressing sintering process. The phase structure and thermal, dielectric and ferroelectric properties of these ceramics were investigated. X-ray measurements showed that all samples have a single perovskite structure and possess orthorhombic–tetragonal and tetragonal–cubic phase transitions. Sequence of phase transitions was confirmed by differential scanning calorimetry (DSC) and dielectric measurements. Obtained results showed that optimal temperature sintering of Na0.5K0.5NbO3+0.5mol%MnO2ceramics is 1100 °C. The results show that investigated ceramics are one of the promising materials as electronic ceramics. [ABSTRACT FROM AUTHOR]

Na0.997Li0.003NbO3ceramics of 93% density have been prepared by a solid-state chemical reaction of stoichiometric mixtures of the component oxides and carbonates. The dielectric, thermal expansion, heat capacity, Raman and ferroelectric studies of these ceramics have been performed. The electric permittivity peak shows rather a small dispersion and no change of the maximum position with increasing frequency can be observed. The results clearly show a first-order phase transition at about 375 °C on heating and near 310 °C on cooling and ambiguously indicated another phase transitions. The pyroelectric measurements show for the first time that the material has weak ferroelectric properties, which are rather metastable. The results show that the investigated ceramics are one of the promising lead-free materials for electronic applications. [ABSTRACT FROM AUTHOR]

Li1.72Na0.28Ge4O9single crystals pure and slightly doped with chromium and manganese, obtained by Czochralski growth, were investigated for their ferroelectric and dielectric properties. The change in stoichometry of Li2−xNaxGe4O9(x = 0.28) crystals doped with Cr and Mn (0.1 mol.%) had an influence on the value of ferroelectric-to-paraelectric phase transition temperature,Tc. The applied doping affects theTcvalue by no more than 10 K. Moreover, we observed strong anisotropy of physical properties of lithium tetragermanate crystals. It has been found that Li1.72Na0.28Ge4O9crystal doped with transition metal ions reveals ferroelectric activity in theb-crystallographic direction, (010 inPca21space group), belowTc = 260 K. This activity, measured by the value of electrical permittivity, is much less for doped crystals than pure ones. Dielectric permittivityε′, conductivity and loss tangent of the crystals, all as the function of temperature in the range of 113–433 K, at frequency between 1 Hz to 1 MHz were measured. The values of conductivity activation energies,Ea, were estimated. Hysteresis loops as well as coercive field and spontaneous polarization were measured and calculated. Switching current transients were analyzed. [ABSTRACT FROM AUTHOR]

Bismuth sodium titanate (Bi0.5Na0.5TiO3; BNT) is one of the most preferred materials for the preparation of lead-free ceramics; however its dielectric property is lower than that of lead-based materials. Thus, the substitution of A and B-site cations is considered to be one of the best solutions in order to improve both the dielectric and piezoelectric properties. In this study, lead-free ceramics from bismuth sodium lanthanum titanate (Bi0.487Na0.487La0.017TiO3; BNLT) and barium titanate (BaTiO3; BT) systems were prepared by a modified two-step mixed oxide method. BT powder was added to BNLT powder with the desired compositions of (1 - x)BNLT-xBT, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10. It was found that the addition of BT in the BNLT improved the electrical properties of ceramics. Phase transition of rhombohedral to tetragonal structure was significantly dependent on the amount of BT added. It was also found that the change in crystal structure affected the ferroelectric property of the ceramics where the transition from ferroelectric to antiferroelectric started from the samples with x ≥ 0.06 mol% and higher. This may be useful in terms of using these materials in the desired applications. [ABSTRACT FROM AUTHOR]

Homogeneous and graded Ba1-xSrxTiO3 ceramics were produced by thick-film technique (tape casting). In the graded materials, the content of strontium was changed from 0 to 30 mol% in the direction normal to the surface. The microstructure, Ba/Sr spatial distribution, polarization characteristics, and dielectric properties of the samples were investigated. No hysteresis loop offset (neither along E- nor P-axis) in the graded Ba1-xSrxTiO3 structures (x = 0-0.3) was observed. This fact was analyzed on the basis of phenomenological models for graded ferroelectrics. The materials with spatially changing composition were characterized by high-temperature stability of dielectric properties and low temperature coefficient of capacitance. [ABSTRACT FROM AUTHOR]

The infrared spectrum of [(C 2 H 5 ) 4 N] 2 SiF 6 was recorded and discussed in relation to its crystal structure. This spectrum indicates that cations and anions are distorted and are not hydrogen bonded. Two structural phase transitions were observed in the tetraethylammonium compound [(C 2 H 5 ) 4 N] 2 SiF 6 by means of dielectric measurements. High-frequency dielectric dispersion phenomena in this compound were also analysed. The evolution of the dielectric constant with the temperature indicates the presence of two phase transitions, at high temperatures, which are of order-disorder character. [ABSTRACT FROM AUTHOR]