The effect of Sb and Nb on the electrical conductivity of tin dioxide based ceramics

The electrical conductivity of Mn doped SnO2 systems prepared by an organic route (Pechini's method) has been investigated as a function of antimony and niobium concentration. The conductivity increases with the increase of both concentration ions, however, in a different manner. While the conductivity of niobium doped ceramics increases with the power of 1.6 for the entire range of concentrations studied (0.01-0.7 mol%), the conductivity of antimony doped ceramics increases with the power of 1.9 in the range 0.01-0.05 mol% of Sb; 3.7 in the range 0.05-0.30 mol% and 1.8 in the range 0.30-0.70 mol%. This behavior is attributed to the existence of two stable oxidation states for antimony: Sb3+ and Sb5+, while for niobium there is only one: Nb5+. The power of 3.7 for Sb would be related to the segregation of this ion on the grain boundary accompanied by an additional contribution coming from the substitution of Sn2+ by Sb3+ on the grain surface.

Ferroelectric and dielectric properties of vanadium-doped Ba(Ti0.90Zr0.10)O-3 ceramics

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Dielectric investigations of vanadium modified barium zirconium titanate ceramics obtained from mixed oxide method

Vanadium modified barium zirconium titanate ceramics Ba(Zr(0.10)Ti(0.90))O(3):2V (BZT:2V) were prepared from the mixed oxide method. According to X-ray diffraction analysis, addition of vanadium leads to ceramics free of secondary phases. Electrical characteristics reveal a dielectric permittivity at around 15,000 with low dielectric loss with a remnant polarization (P(r))of 8 mu C/cm(2) at 2 kV/cm. From the obtained results, we assume that vanadium substitution in the BZT lattice affects dielectric characteristics due to the electron-relaxation-mode in which carriers (polarons, protons, and so on) are coupled with existing dielectric modes. (C) 2009 Published by Elsevier B.V.

Rietveld analysys and electrical properties of lanthanum doped BiFeO3 ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Schottky-type grain boundaries in CCTO ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nanoscale electromechanical properties of CaCu3Ti4O12 ceramics

Piezoresponse Force Microscopy (PFM) is used to characterize the nanoscale electromechanical properties of centrosymmetric CaCu3Ti4O12 ceramics with giant dielectric constant. Clear PFM contrast both in vertical (out-of-plane) and lateral (in-plane) modes is observed on the ceramic surface with varying magnitude and polarization direction depending on the grain crystalline orientation. Lateral signal changes its sign upon 180 degrees rotation of the sample thus ruling out spurious electrostatic contribution and confirming piezoelectric nature of the effect. Piezoresponse could be locally reversed by suitable electrical bias (local poling) and induced polarization was quite stable showing long-time relaxation (similar to 3 hrs). The electromechanical contrast in unpoled ceramics is attributed to the surface flexoelectric effect (strain gradient induced polarization) while piezoresponse hysteresis and ferroelectric-like behavior are discussed in terms of structural instabilities due to Ti off-center displacements and structural defects in this material. (C) 2011 American Institute of Physics. [doi:10.1063/1.3623767]

Effect of heat treatment on the generation of structural defects in LaTaO4 ceramics and their correlation with photoluminescent properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Structural Investigations of Glass Ceramics in the Ga2S3-GeS2-CsCl System

Transparent glass ceramics have been prepared in the Ga2S3-GeS2-CsCI pseudoternary system appropriate heat treatment time and temperature. In situ X-ray diffraction at the heat treatment temperature and Cs-133 and Ga-71 solid-state nuclear magnetic resonance have been performed in function of annealing time to understand the crystallization process. Both techniques have evidenced the nucleating agent role played by gallium with the formation of Ga2S3 nanocrystals. on the other hand, cesium is incorporated very much later into the crystallites during the ceramization. Moreover, the addition of CsCl, which is readily integrated into the glassy network, permits us to shift the optical band gap toward shorter wavelength. Thus, new glass ceramics transmitting in the whole visible range up to 11.5 mu m have been Successfully synthesized from the (Ga2S3)(35)-(GeS2)(25)-CsCl40 base glass composition.

Synthesis and Structural Studies of Er3+ Containing Lead Cadmium Fluoroborate Glasses and Glass-Ceramics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Mineralogical characterization of clays used in the structural ceramic industry in west of S. Paulo State, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Physical and mechanical properties of ceramics from clays of the west of S. Paulo State, Brazil

Argilas de interesse da indústria de cerâmica estrutural foram caracterizadas. Algumas propriedades físicas de diversas massas cerâmicas, preparadas a partir de material coletado em depósitos artificiais, também foram analisadas. Todas as massas investigadas exibem alta concentração de componentes finos (< 2 mim) e considerável grau de plasticidade, o que é compatível com a presença de elevado teor de argilominerais. Corpos de prova cerâmicos foram preparados por prensagem a seco e queimados em temperaturas ao redor de 855 °C. Os parâmetros resistência mecânica à flexão, retração linear, absorção de água, cor aparente e perda de peso foram medidos. Como resultado, as aplicações industriais destas matérias primas foram analisadas e revistas, bem como novas aplicações foram propostas.

Electronic ceramics based on polycrystalline SnO2, TiO2 and (Sn xTi1-x)O2 solid solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis and sintering of PZT ceramics

Lead zirconate powder, with Zr/Ti ratio of 50/50 was prepared by polymeric precursor method and doped with 3, 5 and 7 mol% of Sr+2 Or Ba+2, as well as by 0.2 to 5 mol% of Nb+5. The powder was calcined at 750 degrees C by 4 hours and milled during 1.5 h in isopropilic alcohol. Powders were characterized by surface area measurements (BET method), by infrared spectroscopy and by X-ray diffraction to characterize the crystal structure. Isostatically pressed samples were sintered in a dilatometer furnace by using a constant heating rate of 10 degrees C/min from ambient to 1200 degrees C. Synthetic air and air with water vapor were used as atmospheres. Both Sr+2 and Ba+2 substitute Pb+2 and favor the formation of rhombohedral phase. Otherwise, Nb+5 substitute preferentially Zr+4 favoring tetragonal phase. The concentration of dopants and the atmosphere influence the densification and the microstructure of the PZT, which alters the dielectric and piezoelectric properties of the ceramics.

Microstructure of organometallic derived PLZT ceramics

The PLZT powders with the formula Pb0.905La0.095(Zr0.65Ti0.35)(0.976)O-3+3.5 wt.% PbO were prepared by the organometallic precursor method (Pechini and partial oxalate processes). The microstructure of sintered 9.5/65/35 PLZT ceramics obtained from a partial oxalate procedure shows that the outstanding feature of this microstructure is its fairly uniform grains of about 1.8 mum. The microstructure of sintered PLZT ceramics obtained by the Pechini process consists of uniform small randomly- oriented grains tightly bonded together in the central part of the sample with,a grain size of about 1.2 mum. Cubic and elongated grains are formed at the sample's border. The microstructures of hot pressed PLZT ceramics obtained from both processes are dense and rather uniform. After a double stage of hot pressing (2 plus 20 h) the microstructure of PLZT is fully dense, uniform and homogeneous with a grain size of approximately 2.5 mum. (C) 2001 Elsevier B.V. Ltd. All rights reserved.