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The optimization of the photocatalytic properties of hydrothermal Ti[O.sub.2] were obtained through a systematic investigation of the influence of temperature, pH and control of phase composition and particle morphology. The results suggested that there is correlation between particle morphology and photocatalytic activity.

In the present work, composite ceramics of BaTiO3 with La0.08Pb0.92Ti0.20Zr0.80O3 were prepared from powders synthesized by two different methods: (a) PLZT@BT ceramics from core-shell powders with PLZT-core and BaTiO3 shell and (b) PLZT-BT ceramic composites from mixed PLZT and BaTiO3 powders. In core-shell ceramics, a thin conductive layer of BaPbO3 was formed that resulted in an increased effective permittivity with relatively low losses (tan δ<0.7 in kHz regions). The extrinsic contributions play an important role in both ceramics, but they are more evident in core-shell samples due to the large number of interfaces. These results show that novel functional properties can be tailored by the controlled chemical reaction at interfaces. [ABSTRACT FROM AUTHOR]

It is well known that disordered relaxor ferroelectrics exhibit local polar correlations. The origin of localized fields that disrupt long‐range polar order for different substitution types, however, is unclear. Currently, it is known that substituents of the same valence as Ti4+ at the B‐site of barium titanate lattice produce random disruption of TiOTi chains that induces relaxor behavior. On the other hand, investigating lattice disruption and relaxor behavior resulting from substituents of different valence at the B‐site is more complex due to the simultaneous occurrence of charge imbalances and displacements of the substituent cation. The existence of an effective charge mediated mechanism for relaxor behavior appearing at low (<10%) substituent contents in heterovalent modified barium titanate ceramics is presented in this work. These results will add credits to the current understanding of relaxor behavior in chemically modified ferroelectric materials and also acknowledge the critical role of defects (such as cation vacancies) in lattice disruption, paving the way for chemistry‐based materials design in the field of dielectric and energy storage applications. [ABSTRACT FROM AUTHOR]

Herein, the properties of broadband dielectric spectra up to THz–infrared range of the (1 − x)BaTiO3‐xBaZrO3 (BZT‐x) solid solution are reviewed and complemented. This includes the proper ferroelectric (x = 0), diffuse ferroelectrics (0 < x ≤ 0.2), relaxor ferroelectrics (0.4 ≤ x ≤ 0.8), dipolar glasses (x > 0.8), and the normal dielectric (x = 1). The spectra are characterized by an overdamped central mode in the microwave range which weakens on cooling. Except for BaTiO3, the soft mode and central mode do not soften appreciably and do not contribute substantially to the low‐frequency permittivity maximum. The most important dielectric contribution is brought by Cole–Cole relaxation assigned to hopping of Ti ions in the BaTiO3 clusters, which obeys the Arrhenius law with a common activation energy for the whole relaxor range of Ea ≈ 181±17 meV and broadens on cooling as described by a temperature‐independent distribution of activation energies. It follows that the polar nanoregions within the BaTiO3 clusters remain very small with temperature‐independent size and frozen boundaries, even if the Ti ions inside them are hopping. This differs from the usual lead‐containing relaxors, in which the polar nanoregions grow on cooling and follow the glass‐like freezing. [ABSTRACT FROM AUTHOR]

Composites of poly(vinylidene fluoride) (PVDF) and BaTiO3 nanoparticles (average diameter ca. 125 nm) are fabricated by a solvent‐free and industrially scalable technique, that is, melt blending, followed by compression molding. The effect of processing parameters on the spectroscopic, microstructural, thermal, mechanical and dielectric properties are evaluated as a function of composition (loading up to 30 vol%). The presence of nanoparticle inclusions as well as specific compression molding parameters demonstrate both to affect the molecular relaxations of the PVDF matrix, studied by correlating the results of different techniques, and to induce the PVDF crystallization as β phase. Processing parameters also play a key role for optimizing the dielectric properties. An improved dielectric behavior of the composites is obtained in terms of both permittivity, whose value increases up to four times that of neat PVDF, and dielectric losses, lower than 5% between 10 and 3·104 Hz. The obtained performances resulted enhanced compared to analogous composites prepared with the use of solvents. [ABSTRACT FROM AUTHOR]

In the present work, composite ceramics of ferroelectric BaTiO3 (BT) with magnetic αFE2O3 were prepared from powders synthesized by two different methods: (a) core-shell powders of FE2O3@BT and (b) FE2O3-BT composites from mixed powders with the same composition. The M(H) loops at room temperature show a "wasp-waisted" character, with multiple components, determined as result of the formation of magnetic phases with contrasting coercivities (hard BaFe12O19 and soft Ba12Ti28Fe15O84 phases) in different ratios, as indicated by the magnetic firstorder- reversal curves analysis. The core-shell composite ceramics generally showed slightly improved dielectric properties and smaller conductivity. The high field properties of composite ceramics show a strong nonlinearity in both cases, together with a reduction of zero field permittivity, making from these composites possible tunable materials interesting for applications. Their multifunctional character is enhanced by the presence of a complex magnetic character with soft/ hard components. [ABSTRACT FROM AUTHOR]

The influence of the oxygen vacancies on the dielectric response of BaZr0.10Ti0.90O3 ceramics prepared by solid-state reaction and sintered at 1400 °C for 2 h was investigated. The as-sintered ceramic exhibits a giant relaxation with a shift of the transition temperature from ∼85 °C to above 170 °C in the frequency ranges of 1 Hz-100 kHz, with high losses above unity and two components in the complex impedance plot. A complex dielectric relaxation response, with at least two thermally activated defect mechanisms with activation energies of ∼0.2 eV below the transition temperature and ∼0.7 eV for higher temperatures in the range of 85 °C-170 °C was determined. The observed giant relaxation is an extrinsic effect related to the oxygen deficiency, inhomogeneous distributed in the ceramic grain and not to the relaxor behavior of this system. After a post-annealing treatment at 1000 °C for 50 h, the dielectric response is completely changed: the permittivity vs. temperature dependences present maxima located at around Tm ≈ 90 °C, with almost no frequency dispersion. The conductivity spectra remained almost unchanged after the annealing, showing that the level of oxygen deficiency in this case is related to dielectric relaxations and not to the ac-conductivity dispersion. Two thermally activated dielectric relaxation processes were still identified, but with activation energies of ∼2.7 eV below the transition temperature and of ∼0.87 eV for higher temperatures in the range of 85 °C-170 °C. The high frequency relaxation process is almost suppressed by the reoxidation and its activation energy increased with more than one order in magnitude. One single component in the complex impedance plot found after reoxidation shows that the annealing allowed the homogenization of the oxygen level within the ceramic grains. [ABSTRACT FROM AUTHOR]