A novel nanocomposite was fabricated by introducing BaTiO3 into mesoporous carbon CMK-3 with hexagonal porous structure and pore size around 3.4 nm. Nanosized BaTiO3 crystallites were fully dispersed and confined in the channels of CMK-3. This is the first combination of conventional ferroelectrics with newly developed mesoporous carbon materials. Furthermore, the carbon matrix was thermally removed in oxygen atmosphere to form unique nanoporous structures with the framework of crystalline BaTiO3. The particle morphology evolution from CMK-3 to BaTiO3–CMK-3, and then to porous BaTiO3, was followed by high-resolution scanning electron microscopy (HRSEM). Although this work was aimed at preparation, the present nanocomposite of conductive amorphous carbon and insulate crystalline ferroelectrics, as well as the nanoporous BaTiO3, are expected to have interesting properties in areas such as power storage, microwave adsorbing, and gas sensor.
Potassium tantalate (KTaO3 – KT) ceramics with controlled initial K/Ta ratio = 1, 1.02 and 1.05 were synthesised by solid-state reaction. Crystal structure and microstructure of the sintered ceramics were examined by XRD and SEM/EDS, respectively. Their dielectric properties were then studied as a function of the temperature over the radio frequency range. Ceramics with K/Ta ratio = 1 exhibits potassium-poor secondary phases, in contrast to ceramics with initial K/Ta ratio = 1.05, where no secondary phases are detected. Moreover, the grain size increases dramatically with K/Ta ratio >1. The quantum paraelectric behaviour of KT ceramics is weakly affected by the variation of K/Ta ratio and their dielectric response is well described by Barrett’s equation. Though, no anomaly is induced in the dielectric permittivity by potassium excess, it yields an increase of its lowest temperature magnitude up to ~4000, which is to the best of our knowledge, the highest value ever reported for KT ceramics.
The temperature dependence of the dielectric properties and ac conduction of YMnO3 ceramics annealed under different atmospheres is investigated from 25 to 700 °C. The origin of the dielectric anomalies is clarified. Two dielectric peaks in the permittivity accompanied by a single anomaly in the dielectric losses characterize the dielectric response. Simultaneously, three different regions can be distinguished in the temperature dependence of ac conductivity. Oxygen vacancies with an activation energy for the conduction of 1.13 eV are suggested to be responsible for the dielectric anomaly observed at < 400 °C. For temperatures > 400 °C, the dielectric data are influenced by conductivity and no ferroelectric anomaly is obvious.
Leadzirconatetitanate (PZT, 53/47) fibers are prepared by sol–gel method using organicacids – acrylic and methacrylic acid – to modify the precursors. The macroscopic properties, molecular structure, crystallization behaviour and microstructure of the fibers are investigated as a function of the content and type of acid. Organicacids produce long gel and ceramic fibers, due to the beneficial effect of the long polymeric chains that are generated in the precursor gel. However the longest, strongest, densest and with the highest homogeneity fibers are obtained when acrylic acid is used. The linear shape of the molecular structure of acrylic acid, together with a lower content of organic species to be released, is favourable to the preparation of round and crack free PZT fibers, when acrylic acid is used.
This work reports the effect of lithium doping on the dielectric and polar properties of potassium tantalate. Experimental data were obtained in K1−xLixTaO3 ceramics with x = 0, 0.02, 0.05 and 0.10 by measuring both the dielectric permittivity from 102 to 108 Hz, and polarization under an ac electric field driven at 2.5 Hz, for temperatures from 10 to 300 K. The dielectric permittivity exhibits all the relaxations reported for K1−xLixTaO3 single crystals. Two dielectric relaxations observed at 40–125 K are ascribed to the individual hopping by 90° and 180° of dipoles created by the off-centre Li ions. Another relaxation observed at 100–200 K is related to 180°-flips of Li pairs for x = 0.02 and of polar clusters of interacting Li ions for x = 0.05 and 0.10. In addition to that, an additional relaxation not reported before is presented at 135–235 K for x = 0.10 and attributed to 90°-reorientation of Li polar clusters. Both the change from an Arrhenius to a Vogel–Fulcher dependence with increasing lithium content, and the emergence of slim P (E) hysteresis loops around the relaxation temperatures show that the relaxation dynamics in K1−xLixTaO3 can be understood if a crossover from a dipolar glass to a relaxor-like behaviour is assumed.
Inelastic light scattering is used to study lattice dynamics of strontium titanate (STO) ceramics with several heterovalent dopants (La3+, Gd3+, Y3+), which substitute Sr2+ ions. An extraordinary shift of the antiferrodistortive transition temperature (Ta) is ascertained when just a small percentage of any of the dopants is used. Ta is dependent on the tolerance factor (t). In this work, it is clearly shown that, regardless of the dopant used, a common linear dependence of Ta vs. t is obtained if strontium vacancies are taken into account. A vacancy size of ∼1.547 Å was estimated, which is ∼7% larger than the Sr2+ radius. The vacancy size obtained can directly explain the increase in lattice parameter with increasing Bi3+ content in Bi-doped STO, as opposed to the dopants referred to above. Furthermore, the introduction of La3+, Gd3+ or Y3+ ions at the Sr site causes a considerable stiffening of the transverse optic TO1 mode at low temperatures, thereby decreasing the phonon contribution to the dielectric permittivity. Thus, no traces of a ferroelectric phase are found for any of the dopants used in this work.
A kinetic study of the growth of BaTiO3 under hydrothermal conditions using layered titanate nanotubes as precursors has been performed at 110 and 200 °C. At the early stages of crystallization, irrespective of temperature, pseudocubic BaTiO3 nucleates on the surfaces of the nanotubes. Growth subsequently proceeds by a phase-boundary mechanism with exponent m ≈ 1. During this first regime, “wild type” dendritic particles form with a rough surface and a microstructure which contains planar defects. As the reaction proceeds beyond 70% completion, the nanotubes fully dissolve, and nucleation and growth of tetragonal rather than pseudocubic BaTiO3 take place. During this second regime, the morphology of the BaTiO3 particles remains predominantly dendritic with “seaweed” morphology and a smooth surface, but smaller spherical precipitates and particles with a small number of dendritic arms are also observed. For this stage in the hydrothermal process, the exponent, m ≈ 0.2, does not correspond to any known kinetic mechanisms.
Up until now, no direct evidence of protein adsorption processes associated with polar activity of a piezoelectric has been reported. This work presents the experimental evidence of the protein adsorption process’ dependence on the surface polarization of a piezoelectric by showing at the local scale that the process of protein adsorption is highly favored in the poled areas of a piezoelectric polymer such as poly(L-lactic) acid.
The dielectric response of Sr1-1.5xBixTiO3 films (0.002 ≤ x ≤ 0.167), prepared by sol-gel and deposited on Si/SiO2/TiO2/Pt substrates, is analyzed as a function of frequency and temperature. The hysteretic behavior of the polarization versus the electric field is studied as well. Between 100 Hz and 1 MHz, the real part of the dielectric permittivity ɛ′ exhibit a relaxation between ∼60 and 260 K, shifting to high temperatures with increasing the Bi content. In the imaginary part of the dielectric permittivity ɛ” of these films two relaxations are induced by Bi doping below the temperature of the ɛ’ relaxation. The first relaxation observed in films with 0.002 ≤ x ≤ 0.10 follows the Arrhenius law with an activation energy of U = 64–80 meV and a preexponential term τ0 = (0.3–10.8) × 10−14 s almost independent on the Bi content and is ascribed to the individual hopping of dipoles created by the off-center Bi ions. The second relaxation observed in the films with 0.04 ≤ x ≤ 0.167 is described by the Vögel–Fulcher relation with U = 2–38 meV, τ0 = 5 × 10−10–5 × 10−6 s and a freezing temperature Tf = 50–102 K, increasing with Bi content, and is attributed to the presence of polar clusters of interacting Bi ions. Slim P(E) hysteresis loops are observed at low temperatures, confirming the appearance of a polar state. The effect of Bi incorporation in ST films is qualitatively the same as the relaxorlike behavior observed in Bi-doped ST ceramics and the dissimilarities are explained based on the influence of the substrate and by a higher homogeneity of the dopant distribution in the sol-gel derived films.
The influence of the neutralization process after hydrothermal synthesis on the structure and morphology of titanate nanotubes was investigated by X-ray diffraction, high-resolution transmission electron microscopy and Raman spectroscopy. Well formed nanotubes were obtained during the hydrothermal treatment of anatase in highly alkaline conditions. Synthesis at 150 degrees C led to the formation of layered titanate structure with the general formula Na(2-x)H(x)Ti(2)O(5)center dot 1.8 H(2)O, where x depends on pH. The tubular morphology is not dependent on the Na(+)/H(+) ion exchange reaction.
The effect of Sr vacancies on the behavior of strontium titanate with trivalent dopants (La3+, Gd3+, and Y3+) substituting Sr2+ ions is reported. A remarkable shift of the antiferrodistortive transition temperature Ta is revealed by Raman spectroscopy for just a small content of dopant. It is shown that a unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are taken into account. A vacancy size value of ∼ 1.54 Å is estimated, which is ∼ 7% larger than Sr2+ radius. This size difference enables explaining the unexpected increase of lattice parameter with increasing Bi3+ content in Sr1−1.5xBixTiO3.