Perovskite-Based Mesostructures and Related Composites — Influence Exerted by Morphology and Interface

The present work seeks to report about the properties of lead-free NaNbO3 particles with different morphology (cubic-like and fiber-like particles) and their application in composites with poly(vinylidenefluoride) (PVDF) polymer. The composites are obtained using a range of varying volume fractions of NaNbO3 particles (30%, 40%, 50% and 60%). The best conditions for obtaining the NaNbO3 particles as well as the composites have been thoroughly studied. It was observed that the highest volume fraction of NaNbO3 particles undermined the flexibility of the composites. The transition percolation phenomenon, commonly known as percolation threshold, was calculated as a function of the dielectric constant and conductivity of the composite. The composites exhibit piezoelectric and ferroelectric properties and both are found to improve by anisotropy of the NaNbO3 particles

Jeans: a relação entre aspectos científicos, tecnológicos e sociais para o Ensino de Química

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New Approaches to Preparation of SnO2-Based Varistors — Chemical Synthesis, Dopants, and Microwave Sintering

Tin oxides have applications such as sensors, solar cells, transistors, and varistors, which are being studied to replace ZnO varistors due to similar electrical properties, simpler microstructure, no formation of secondary phases, and lower concentration of agent modifiers to promote the varistor characteristics and densification. Varistors are ceramic with a high concentration of structural and electronics defects. The type and the amount of defects are related with agent modifiers and processing steps employed. The study in materials processing aims to improve the ceramics properties. Chemical synthesis ensures the homogeneous distribution of dopants used to promote electrical and structural properties. Microwave sintering appears as processing to optimize time and sintering temperature. Varistor application is linked to its breakdown voltage, which should be larger than the operating voltage. In an operating range of 1 kV to 1 MV, the varistors are used in electricity transmission networks. In a range of 24–1000 V, the application occurs in electronics and appliances and in a range smaller than 24 V, as protective of automotive electronics and computers. This chapter aims to provide information on new processing steps for the production of SnO2 varistors and to show the possibility to get electrical properties with non-ohmic characteristic for technological applications

PROPERTIES OF LANTHANUM DOPED BARIUM TITANATE PRODUCED FROM NANOPOWDERS

As a first discovered ferroelectric ceramic, barium titanate has become one of the most extensively investigated ceramic materials used in electronics. For many years, A- and B-site dopants have been used to modify the electrical properties of BaTiO3. in this paper, barium titanate doped with 0.3 mol% of lanthanum and sintered at different sintering times was investigated. Doped barium titanate nanopowder was prepared by doping pure barium titanate starting from citrate solutions of all components: barium, titanium and lanthanum. Experimental procedure was given in detail in previous reports. Obtained powders were pressed in to pellets and sintered at 1300 "C for 2 and 16h in air atmosphere. The formation of phase and crystal structure of BaTiO3 was carried out by XRD analysis. Microstructural properties such as grain size distribution and morphology of sintered samples were determined using scanning electron microscope. Measurement of dielectric constant and dielectric losses was provided in the frequency range of 20 to 106 Hz. The variation of the dielectric constant with temperature was measured in temperature interval from 20 to 180 oC. . The XRD analysis of doped barium titanate indicates the formation of tetragonal phase in samples sintered at both sintering times. Lanthanum has an influence on grain growth and shape of grains in doped barium titanate [2]. It was detected that the grain-size also depends on sintering time. It can be notified the effect of lanthanum and sintering time on dielectric constant. Lanthanum also has influence on decreasing the Curie temperature of barium titanate. No frequency dependence of dielectric constant,was detected

EFFECT OF POWDER SYNTHESIS ON CRYSTAL AND MICROSTRUCTURE OF BaTiO3

Barium titanate (BaTiO3) has been used in many applications such as multilayer capacitors, piezoelectric ceramics, transducer devices, PTC resistor and has become one of the most important ferroelectric ceramics. It is used extensively in ceramic capacitors, due to its high dielectric constant and low loss characteristics. Barium titanate was prepared by two methods, polymeric organometallic precursors process and mechanochemicaly. X ray and SEM were used for caracterization of powders and sintered samples. In both ways of synthesis the formation of cubic phase is obtained. It can be observed that in the case of Pechini process BaTiO3 powder is well crystallized but in the case of mechanochemically process, significant amount of amorphous phase was detected. The sintered samples at 1300'C for 2h, prepared by Pechini process, shows the formation of tetragonal phase. The morphology of the powders consists of particles and its agglomerates, their dimensions depend of the synthesis method. The powder prepared mechanochemicaly posses more agglomerates. The particles are bigger and with irregular shape. Average particle size is about 100 nm and 250 nm for Pechini and mechanochemical process, respectively. In sintered samples, prepared by Pechini process, at 1300oC for 2h is observed two types of domain configuration. The wall thickness ranges from 0.08 pm up to 0.14 pm and from 0.14 Fm up to 0.17 pm for 90' and 180'domains respectably. The domain width is around 0.20 micron for both types of domains

Biochars from Spirulina as an alternative material in the purification of lactic acid from a fermentation broth

In this study, Spirulina biochar obtained from fast pyrolysis was evaluated as an alternative to commercial activated carbon for lactic acid (LA) purification from a fermentation broth. Thermally (350 and 400 C treatment of the biochar in N2 atmosphere for 4 h) and chemically (KOH solution impregnation of the algal material and fast pyrolysis to obtain the biochar) activated Spirulina biochars were also tested. The biochars were previously characterized using SEM and FT-IR. Two purification methodologies were evaluated: filtration and stirring. The stirring method prove to be simpler, faster and chipper, with excellent purification results. All the evaluated biochars presented a performance comparable to that of activated carbon in the stirring methodology. Spirulina biochar and the KOH activated biochar were the once with the best results, with 92 and 82% LA recovery and 82 and 90% protein removal efficiencies, respectively.Fil: Piloni, Roxana Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Coelho, Luciana Fontes. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Sass, Daiane Cristina. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Lanteri, Mario Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones y Transferencia de Villa María. Universidad Nacional de Villa María. Centro de Investigaciones y Transferencia de Villa María; ArgentinaFil: Bertochi, Maria Aparecida Zaghete. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Moyano, Elizabeth Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Contiero, Jonas. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi

Direct preparation of standard functional interfaces in oxide heterostructures for 2DEG analysis through beam-induced platinum contacts

Two-dimensional electron gas (2DEG) in SrTiO3/LaAlO3 heterostructures has been extensively studied in the last few years; however, little attention has been given to a practical way to contact electrically the low dimensional gas at the interface. This work demonstrates a method to contact the 2DEG formed at the oxide interfaces connected by platinum electrodes which were made by the decomposition of organometallic gas using focused ion beams. On the surface, the electrodes were defined through photolithography, and at the interface, the electrodes were deposited through the focused ion beams and electrons, which were then evaluated. The quality of the interface electrodes was evaluated at two different partial oxygen pressures (pO2) used for the film deposition: low (10−4 mbar) and high (10−1 mbar). The electrode deposition conditions using electrons or ions have resulted in different rates of metal deposition and interaction with the interface leading to either metallic (2DEG) or insulating behavior

NZF-BT COMPOSITES: A PHOTOLUMINESCENCE APPROACH

Photoluminescence (PL) analysis provide us important information about the structure of materials, however the PL behavior of (x)Ni0.7Zn0.3Fe2O4-(1-x)BaTiO3 ((x)NZF-(1-x)BT) multiferroic composites is not very well know. Based on this, (x)NZF-(1-x)BT powders whit different ratio of NZF/BT (x= 0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by auto-combustion method. After that, the PL property of the composites was explored through measurements carried out using as excitation source a krypton laser with wavelength of 350 nm. The presence of PL emission suggests that the structures of the materials are medium range disordered. Oxygen vacancies (anion vacancies), metal vacancies (cation vacancy) and lattice distortion are responsible by PL emission due to formation of structural defects which are essential to promote the electronic transitions inside band gap. Emission at low energy (green/yellow/red) occurs due to deep defects which modify the Fermi level generating intermediary levels near the conduction band. On the other hand, PL emission at high energy region (violet/ blue) is originated by the presence of shallow defects which generate states next to the valence band. In the present work, all samples showed a broad band emission centered around 450 nm (Figure 1), being a region characteristic of contribution of shallow defects for photoluminescence emission. In addition, the PL broad band emission is an evidence of structural disorder in the lattice of materials which promotes the formation of numerous states within the band gap