BaTiO3 thick fi lms obtained by tape casting from powders prepared by the oxalate route

BaTiO3 powders were prepared by co-precipitation via oxalate route. The size, morphology and particle size distribution of the oxalate powders have been optimized by the control of different synthesis parameters during the precipitation reaction (nature of salts, concentration of different solutions, aging time). The single phase BaTiO3 oxide particles were obtained after a thermal decomposition of the as-synthesized powders at 850°C for 4 hours under air atmosphere. Oxide powders with a suitable specifi c surface area were selected in order to obtain thick fi lms by the tape casting technique. The microstructure and dielectric properties of the thick films varied obviously depending on the deposition-calcination-sintering cycle used. A double depositioncalcination cycle followed by sintering, as well as a two step deposition-calcination-sintering procedure was used in order to improve the compactness and therefore, the dielectric behaviour. A higher dielectric constant value (~ 750) and lower dielectric losses (~ 2 %) were achieved at room temperature and at 1 kHz frequency for the dense, double-deposited fi lm obtained after two deposition-calcination-sintering cycles. For this film, a superior value of the dielectric constant (~ 1100), almost frequency independent in the frequency range of 100 Hz – 10 kHz was gained also at the ferroelectric-paraelectric phase transition temperature of 130°C

Temperature dependent tunability data and modelling in the paraelectric Ba0.7Sr0.3TiO3 solid solutions

The fi eld dependence of the dielectric constant (dc-tunability) as a function of temperature in (Ba,Sr)TiO3 ceramics was investigated. Dense and homogeneous BaxSr1-xTiO3 ceramics prepared by Pechini method show low losses, high dielectric constant of ~4000 and typical ferroelectric properties at room temperature. The dctunability at various temperatures, including the Curie range, was obtained. A single polarization mechanism was used in the polar state of the ceramics to describe the tunability data. A good correlation between theory and experiment was found. In the paraelectric phase, a model of random uncorrelated non-interacting dipolar units in a double well potential was considered

Lanthanum Ferrite Ceramic Powders: Synthesis, Characterization and Electrochemical Detection Application

The perovskite-type lanthanum ferrite, LaFeO3, has been prepared by thermal decomposition of in situ obtained lanthanum ferrioxalate compound precursor, LaFe(C2O4)3·3H2O. The oxalate precursor was synthesized through the redox reaction between 1,2-ethanediol and nitrate ion and characterized by chemical analysis, infrared spectroscopy, and thermal analysis. LaFeO3 obtained after the calcination of the precursor for at least 550–800 °C/1 h have been investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). A boron-doped diamond electrode (BDD) modified with LaFeO3 ceramic powders at 550 °C (LaFeO3/BDD) by simple immersion was characterized by cyclic voltammetry and tested for the voltammetric and amperometric detection of capecitabine (CCB), which is a cytostatic drug considered as an emerging pollutant in water. The modified electrode exhibited a complex electrochemical behaviour by several redox systems in direct relation to the electrode potential range. The results obtained by cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and multiple-pulsed amperometry proved the electrocatalytic effect to capecitabine oxidation and reduction and allowed its electrochemical detection in alkaline aqueous solution

CuBi2O4 Synthesis, Characterization, and Application in Sensitive Amperometric/Voltammetric Detection of Amoxicillin in Aqueous Solutions

CuBi2O4 synthesized by thermolysis of a new Bi(III)-Cu(II) oxalate coordination compound, namely Bi2Cu(C2O4)4·0.25H2O, was tested through its integration within carbon nanofiber paste electrode, namely CuBi/carbon nanofiber (CNF), for the electrochemical detection of amoxicillin (AMX) in the aqueous solution. Thermal analysis and IR spectroscopy were used to characterize a CuBi2O4 precursor to optimize the synthesis conditions. The copper bismuth oxide obtained after a heating treatment of the precursor at 700 °C/1 h was investigated by an X-ray diffraction and scanning electron microscopy. The electrochemical behavior of CuBi/CNF in comparison with CNF paste electrode showed the electrocatalytic activity of CuBi2O4 toward amoxicillin detection. Two potential detections, with one at the potential value of +0.540 V/saturated calomel electrode (SCE) and the other at the potential value of −1.000 V/SCE, were identified by cyclic voltammetry, which were exploited to develop the enhanced voltammetric and/or amperometric detection protocols. Better electroanalytical performance for AMX detection was achieved for CuBi/CNF using differential-pulsed and square-wave voltammetries than others reported in the literature. Very nice results obtained through anodic and cathodic currents recorded at +0.750 V/SCE and −1.000 V/SCE in the same time period using a pseudo multiple-pulsed amperometry technique showed the great potential of the CuBi/CNF paste electrode for practical applications in amoxicillin detection in aqueous solutions

Influence of Sintering Strategy on the Characteristics of Sol-Gel Ba1−xCexTi1−x/4O3 Ceramics

Single-phase Ce3+-doped BaTiO3 powders described by the nominal formula Ba1−xCexTi1−x/4O3 with x = 0.005 and 0.05 were synthesized by the acetate variant of the sol-gel method. The structural parameters, particle size, and morphology are strongly dependent on the Ce3+ content. From these powders, dense ceramics were prepared by conventional sintering at 1300 °C for 2 h, as well as by spark plasma sintering at 1050 °C for 2 min. For the conventionally sintered ceramics, the XRD data and the dielectric and hysteresis measurements reveal that at room temperature, the specimen with low cerium content (x = 0.005) was in the ferroelectric state, while the samples with significantly higher Ce3+ concentration (x = 0.05) were found to be in the proximity of the ferroelectric–paraelectric phase transition. The sample with low solute content after spark plasma sintering exhibited insulating behavior, with significantly higher values of relative permittivity and dielectric losses over the entire investigated temperature range relative to the conventionally sintered sample of similar composition. The spark-plasma-sintered Ce-BaTiO3 specimen with high solute content (x = 0.05) showed a fine-grained microstructure and an almost temperature-independent colossal dielectric constant which originated from very high interfacial polarization

Hydrothermal Synthesis of SrTiO3: Role of Interfaces

The hydrothermal synthesis of SrTiO3 in a Sr(OH)(2)/NaOH solution by reaction of four different single crystalline titanium precursors (anatase, rutile, sodium titanate, and hydrogen titanate) having the same nanowire morphology was investigated under stagnant fluid conditions. Owing to the low solubility and dissolution rate of the parent phases, the reaction mainly occurs in a thin interfacial fluid layer. The new phase only grows on the substrate surface, and the morphology evolution is largely controlled by the interface through the coupling of substrate dissolution and SrTiO3 crystallization. The pseudomorphic replacement of the precursor by the product occurs if complete surface coverage is attained. Depending on the crystallographic matching, the parent crystal can either transform in a mesocrystal as happens with anatase via a topochemical transformation or in a polycrystalline product as observed with sodium titanate. In contrast, if the product grows in the form of isolated particles or with dendritic morphology, as in the case of hydrogen titanate and, to a lesser extent rutile, the new compound will not inherit the precursor morphology. When well-defined interfaces are missing, as happens when amorphous titanium hydroxide gel suspensions are used as precursors, the crystallization of SrTiO3 occurs by a completely different pathway, i.e., oriented self-assembly of nanocrystals in mesocrystals

Effect of nanostructure on the thermal conductivity of La-doped SrTiO3 ceramics

A series of La-doped (10 at.%) SrTiO 3 ceramics with grain size ranging from 6 m to 24 nm was prepared from nanocrystalline powders using high-pressure field assisted sintering (HP-FAST). A progressive reduction of thermal conductivity \u3ba with decreasing grain size was observed. At room temperature, \u3ba of the ceramic with grain size of 24 nm (1.2 W m 12 1 K 12 1 ) is one order of magnitude lower than that of undoped single crystals. The strong suppression of \u3ba can be ascribed to (i) the high concentration of lattice defects, (ii) the increasing contribution of grain boundaries to phonon scattering when the grain size is decreased to the nanoscale and (iii) a moderate amount (10\u201315 vol.%) of nanopores. These results demonstrate that nanostructuration can be a successful strategy to attain a considerable reduction of \u3ba in heavily doped bulk oxide ceramics. The low electrical conductivity of the La:SrTiO 3 nanoceramics represents a major obstacle for thermoelectric applications