Study of Ti-modified columbite route and the effect of lithium doping in 0.9PMN-0.1PT ceramics

The influence of lithium on the structural characteristics of PMN-PT ceramic was studied. The synthesis of PMN-PT powders using this precursor leads to the formation of high amount of perovskite phase. The insertion of Li(+) ions in B-site affects the microstructure because the rise in mass transport changes the mechanical characteristics of sintered ceramic. Higher values of K(m) and T(m) were gotten when lithium is inserted into perovskite phase. Secondary phase was found when lithium content increase beyond 1 mol%, besides the occurrence of transgranular fractures in sintered ceramic. Also, the additive acts increasing the relaxor behavior.

Mechanochemical synthesis of barium titanate

A powder mixture of BaO and TiO2, was mechanochemically treated in a planetary ball mill in an air atmosphere for up to 4 h, using zirconium oxide vial and zirconium oxide balls as the milling medium. Mechanochemical reaction leads to the gradual formation of BaTiO3 phase. Phase evolution during synthesis and changes in powder size and morphology were monitored by XRD, DSC, IR and TEM analysis and it was shown that the formation of BaTiO3 phase was initiated after 60 min. Extended time of milling directed to formation of higher amount of BaTiO3 perovskite phase. Barium titanate with good crystallinity was formed after 240 min sintering without pre-calcination step was performed at 1330 degrees C for 2 It within heating rate 10 degrees C/min. (c) 2005 Elsevier Ltd. All rights reserved.

Room-temperature photoluminescence of BaTiO3: Joint experimental and theoretical study

Strong photoluminescent emission has been measured at room temperature for noncrystalline BaT'O-3 (BT) perovskite powders. A joint experimental and theoretical study has been carried out to rationalize this phenomenon. From the experimental side, BT powder samples have been synthesized following a soft chemical processing, their crystal structure has been confirmed by x-ray data and the corresponding photoluminescence (PL) properties have been measured. Only the structurally disordered samples present PL at room temperature. From the theoretical side, first-principles quantum-mechanical techniques, based on density-functional theory at the B3LYP level, have been employed to study the electronic structure of crystalline (BT-c) and asymmetric (BT-a) models. Theoretical and experimental results are found to be consistent and their confrontation leads to an interpretation of the PL apparition at room temperature in the structurally disordered powders.

Influence of seed particle frequency on the phase formation and on the microstructure of 0.88 PZN-0.07 BT-0.05 PT ceramic

The Pechini method as well as the simultaneous addition of seeds particles and dopant solutions of BaTiO3 (BT) and PbTiO3 (PT) were used to prepare the perovskite phase 0.88 PZN-0.07 BT-0.05 PT. To study the influence of seed particle frequency on the synthesis of the PZN ceramic, two ranges of seed particle size were used: the range from 30 to 100 nm, termed small seed particles (frequency of 10(15) particles/cm(3)); and the range from 100 to 900 nm, termed large seed particles (frequency of 10(13) particles/cm(3)). The crystalline nuclei size influenced the calcining process, the sintering process and the microstructure. Samples prepared with lower seed frequency displayed more amount of pyroclore phase, need higher temperatures for sintering and showed a more heterogeneous microstructure with poor dielectric properties. (C) 2000 Elsevier B.V. Ltd and Techna S.r.l. All rights reserved.

In situ solid state oxidation reaction for La1-xSrxMnO3 (x=0, 0.1, 0.2 and 0.3) formation

In situ solid state oxidation reaction for an alternative La1-xSrxMnO3 (x = 0, 0.1, 0.2 and 0.3) formation is reported. Samples have been obtained by using strontium peroxide, lanthanum and manganese (III) oxide reagents. Strontium peroxide has induced the oxidation of Mn+3 to Mn+4. Lanthanum strontium-doped manganite was obtained without secondary phase formation. La0.825Sr0.175MnO3 showed two structural transitions. The first from 88 to 373 K and the second at 1073 K. which are explained by Jahn-Teller effect at low temperature and cation displacement at high temperature. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Influence of the LiNbO3 and KNbO3 seeds on the sintering and electrical properties of PMN ceramic

The effect of LiNbO3 and KNbO3 seeds on the microstructure and dielectric characteristics of PMN ceramic prepared by columbite route have been investigated with the addition of 0, 1, and 2-wt% of seeds. X-ray diffraction, Scanning Electron Microscopy and an impedance analyzer were used to characterize the influence of seeds on physical characteristics and dielectric properties of PMN. LiNbO3 -seeded PMN samples present a significant increase in the amount of perovskite phase. The addition of LiNbO3 seeds in sintered PMN ceramics at 1100degreesC during 4 h causes a decrease in the porosity and the amount of pyrochlore phase. Weight losses during sintering of PMN ceramics are suppressed more significantly for LiNbO3 -seeded PMN. T-m of PMN ceramics changes with seeds concentration. KNbO3 seeds displace T-m to lower temperature whereas LiNbO3 causes its elevation. Dielectric constants of approximately 13,000 at 1 kHz was measured at -5degreesC in PMN ceramics with 1-wt% of LiNbO3 seeds.

Mechanochemical synthesis of PZT powders

PZT ceramic powders were successfully prepared from the mixture of PbO, ZrO2 and TiO2 by mechanochemical synthesis in a planetary ball mill, under different milling conditions. Phase evolution during synthesis was monitored by X-ray diffraction analysis. Intensive milling resulted in formation of the nanocrystalline, perovskite PZT powders after 1 h of milling. This is a significant improvement in comparison to milling conditions reported by other authors. Depending on milling parameters the presence of some other phases, such as unreacted ZrO2, was also detected in some samples. The changes in powder size and morphology due to intensive milling, were determined by SEM and TEM, while BET analysis was used to determine specific surface area of the powders. Conclusions about processes taking place during mechanochemical synthesis of PZT powders were made based on the results of characterization. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Thermal properties of fluoride glasses and their gel precursors

Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.

Glass structure and ion dynamics of lead-cadmium fluorgermanate glasses

Glass structure and fluorine motion dynamics are investigated in lead-cadmium fluorgermanate glasses by means of differential scanning calorimetry, Raman scattering, x-ray absorption (EXAFS), electrical conductivity (EC), and F-19 nuclear magnetic resonance (NMR) techniques. Glasses with composition 60PbGeO(3)-xPbF(2)-yCdF(2) (in mol %), with x+y=40 and x=10, 20, 30, 40, are studied. Addition of metal fluorides to the base PbGeO3 glass leads to a decrease of the glass transition temperature (T-g) and to an enhancement of the ionic conductivity properties. Raman and EXAFS data analysis suggest that metagermanate chains form the basic structural feature of these glasses. The NMR study leads to the conclusion that the F-F distances are similar to those found in pure crystalline phases. Experimental results suggest the existence of a heterogeneous glass structure at the molecular scale, which can be described by fluorine rich regions permeating the metagermanate chains. The temperature dependence of the NMR line shapes and relaxation times exhibits the qualitative and quantitative features associated with the high fluorine mobility in these systems. (C) 2004 American Institute of Physics.

Ferroelectric properties of mechanically synthesized nanosized barium titanate

Barium titanate ceramics were prepared through mechanochemical synthesis starting from fresh prepared barium oxide and titanium oxide in rutile form. Mixture of oxides was milled in zirconia oxide jar in the planetary ball-mill during 30, 60, 120 and 240 min. Extended time of milling directed to formation of higher amount of barium titanate perovskite phase. Barium titanate with good crystallinity was formed after 240 min. Sintering without pre-calcinations step was performed at 1330 degrees C for 2 hours with heating rate of 10 degrees C/min. The XRD, DSC, IR and TEM analyses were performed. Electric and ferroelectric properties were studied. Very well defined hysteresis loop was obtained.

Microwave synthesis of calcium bismuth niobate thin films obtained by the polymeric precursor method

The crystal structure, surface morphology and electrical properties of layered perovskite calcium bismuth niobate thin films (CaBi2Nb2O9-CBN) deposited on platinum coated silicon substrates by the polymeric precursor method have been investigated. The films were crystallized in a domestic microwave and in a conventional furnace. X-ray diffraction and atomic force microscopy analysis confirms that the crystallinity and morphology of the films are affected by the different annealing routes. Ferroelectric properties of the films were determined with remanent polarization P-r and a drive voltage V-c of 4.2 mu C/cm(2) and 1.7 V for the film annealed in the conventional furnace and 1.0 mu C/cm(2) and 4.0 V for the film annealed in microwave furnace, respectively. A slight decay after 10(8) polarization cycles was observed for the films annealed in the microwave furnace indicating a reduction of the domain wall mobility after interaction of the microwave energy with the bottom electrode. (C) 2006 Elsevier Ltd. All rights reserved.

Investigation on possibility of mechanochemical synthesis of CaTiO3 from different precursors

Recently, mechanochemical synthesis was widely used in preparation of perovskite type of materials, such as BaTiO3, PbTiO3, PZT, etc. In this work, the possibility of mechanochemical synthesis of CaTiO3 from different precursors, such as CaCO3 or CaO and TiO2 was investigated. Intensive milling of mixture of CaO and TiO2, under optimal milling conditions, resulted in synthesis of single phase CaTiO3. It was also found that intensive milling of powder mixture containing CaCO3 and TiO2 only activate the powders for the sintering process; hence the CaTiO3 could be obtained at lower temperatures of sintering. To complete reaction of CaTiO3 formation during milling it is necessary to reduce CO2 partial pressure, i.e. it is necessary to change the atmosphere inside the vials during milling. In this work, an explanation for difference in milling behavior of different precursors was proposed and discussed. (c) 2006 Elsevier Ltd. All rights reserved.

Improvement of the chemical resistance of zirconium fluoride glasses coated with a Tiron (R) modified tin oxide layer prepared by the sol-gel process

In order to improve the chemical resistance of zirconium fluoride glass a protective transparent SnO2 layer was deposited by the solgel dip-coating process in the presence of Tiron (R) as particle surface modifier agent. After water immersion for different periods of time, both coated and non-coated fluoride glasses were analyzed by scanning electron microscopy, mass loss evaluation, infrared spectroscopy and X-ray photoelectron spectroscopy. In contrast to the effects occurring for non-coated glass, where the surface undergoes a rapid selective dissolution of the most soluble species, the results for the SnO2-coated glass showed that the filling of the film nanopores by dissolved glass material results in a hermetic barrier protecting the glass surface. The selective glass dissolution was confirmed by liquid chromatography measurements of the etching solution after each exposure time. (c) 2006 Elsevier B.V. All rights reserved.

Preparation of Pb(Zr,Ti)O-3 thin films by soft chemical route

Lead zirconate titanate, Pb(Zr0.3Ti0.7)O-3 (PZT) thin films were prepared with success by the polymeric precursor method. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), Micro-Raman spectroscopy and X-ray diffraction (XRD) were used to investigate the formation of the PZT perovskite phase. X-ray diffraction revealed that the film showed good crystallinity and no presence of secondary phases was identified. This indicates that the PZT thin films were crystallized in a single phase. PZT thin films showed a well-developed dense grain structure with uniform distribution, without the presence of rosette structure. The Raman spectra undoubtedly revealed these thin films in the tetragonal phase. For the thin films annealed at the 500-700 degreesC range, the vibration modes of the oxygen sublattice of the PZT perovskite phase were confirmed by FT-IR. The room temperature dielectric constant and dielectric loss of the PZT films, measured at 1 kHz were 646 and 0.090, respectively, for thin film with 365 nm thickness annealed at 700 degreesC for 2 h. A typical P-E hysteresis loop was observed and the measured values of P-s, P-r and E-c were 68 muC/cm(2), 44 muC/cm(2) and 123 kV/cm, respectively. The leakage current density was about 4.8 x 10(-7) A/cm(2) at 1.5 V. (C) 2003 Elsevier Ltd. All rights reserved.

Contactless measurement of colossal magnetoresistance in La1-xSrxMnO3 using the infrared magnetorefractive effect

The magnetorefractive effect (MRE) has been used for the first time to study the magnetotransport properties of La1-xSrxMnO3 perovskite materials. A direct correlation between the MRE and colossal magnetoresistance was observed. Samples with x = 0-0.3 prepared using the homogeneous coprecipitation and the solid state reaction methods were studied, covering the range of insulating to metallic behaviour. The M RE probed both the magnetically induced modification of the scattering of Drude-like electrons and the magnetic dependence of a stretching vibration mode. (C) 2004 Elsevier B.V. All rights reserved.