Effect of annealing atmosphere on phase formation and electrical characteristics of bismuth ferrite thin films

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

Effect of processing route on the phase formation and properties of Bi4Ti3O12 ceramics

Our efforts were directed to the preparation of bismuth titanate-Bi4Ti3O12 (BIT) by two procedures: mechanically assisted synthesis and polymeric precursor method to display a variety of their advantages. To follow the nucleation and phase formation of BIT, XRD and Rietveld refinement analysis were used and it was shown that Bi4Ti3O12 ceramic can been successfully prepared from nano-sized powders obtained by both methods. The ferroelectric properties were determined and the loops from BIT obtained by polymeric precursor method were not fully saturated with a remnant polarization of 20 mu C/cm(2) and coercitive field of 1500 kV/cm. BIT obtained from powders prepared by mechanically assisted synthesis shows a remnant polarization of 0.65 mu C/cm(2) and coercitive field of 1050 kV/cm. The grain morphology may be the factor causing the observed differences. (C) 2005 Published by Elsevier Ltd and Techna Group S.r.l.

BERRY PHASE, AHARONOV-BOHM EFFECT AND TOPOLOGY

The Berry phase for an electron in a one-dimensional box rotated around a magnetic flux line has contributions from the geometry and the magnetic flux, which gives an Aharonov-Bohm effect. For a circular box enclosing the magnetic flux, the Berry phase depends on the boundary conditions.

Effect of Ag addition on phase transitions of the Cu-22.26 at.%Al-9.93 at.%Mn alloy

The phase transitions that occur in the Cu-22.26 at.%Al-9.93 at.%Mn and Cu-22.49 at.%Al-10.01 at.%Mn-1.53 at.%Ag alloys after slow cooling were studied using differential scanning calorimetry at different heating rates, microhardness changes with temperature, magnetization changes with temperature, scanning electron microscopy and energy dispersion X-ray spectroscopy. The results indicated that the presence of Ag does not modify the transition sequence of Cu-Al-Mn alloy, introduces a new transition due to the (Ag-Cu)-rich precipitates dissolution at about 800 K, and changes the mechanism of DO 3 phase dissolution. This mechanistic change was analyzed and a sequence of phase transitions was proposed for the reaction. © 2013 Elsevier B.V.

Effect of air-particle abrasion protocols on the biaxial flexural strength, surface characteristics and phase transformation of zirconia after cyclic loading

This study evaluated the effect of air-particle abrasion protocols on the biaxial flexural strength, surface characteristics and phase transformation of zirconia after cyclic loading. Disc-shaped zirconia specimens (Ø: 15mm, thickness: 1.2mm) (N=32) were submitted to one of the air-particle abrasion protocols (n=8 per group): (a) 50μm Al2O3 particles, (b) 110μm Al2O3 particles coated with silica (Rocatec Plus), (c) 30μm Al2O3 particles coated with silica (CoJet Sand) for 20s at 2.8bar pressure. Control group received no air-abrasion. All specimens were initially cyclic loaded (×20,000, 50N, 1Hz) in water at 37°C and then subjected to biaxial flexural strength testing where the conditioned surface was under tension. Zirconia surfaces were characterized and roughness was measured with 3D surface profilometer. Phase transformation from tetragonal to monoclinic was determined by Raman spectroscopy. The relative amount of transformed monoclinic zirconia (FM) and transformed zone depth (TZD) were measured using XRD. The data (MPa) were analyzed using ANOVA, Tukey's tests and Weibull modulus (m) were calculated for each group (95% CI). The biaxial flexural strength (MPa) of CoJet treated group (1266.3±158A) was not significantly different than that of Rocatec Plus group (1179±216.4A,B) but was significantly higher than the other groups (Control: 942.3±74.6C; 50μm Al2O3: 915.2±185.7B,C). Weibull modulus was higher for control (m=13.79) than those of other groups (m=4.95, m=5.64, m=9.13 for group a, b and c, respectively). Surface roughness (Ra) was the highest with 50μm Al2O3 (0.261μm) than those of other groups (0.15-0.195μm). After all air-abrasion protocols, FM increased (15.02%-19.25%) compared to control group (11.12%). TZD also showed increase after air-abrasion protocols (0.83-1.07μm) compared to control group (0.59μm). Air-abrasion protocols increased the roughness and monoclinic phase but in turn abrasion with 30μm Al2O3 particles coated with silica has increased the biaxial flexural strength of the tested zirconia. © 2013 Elsevier Ltd.

Effect of the ZrO2 phase on the structure and behavior of supported Cu catalysts for ethanol conversion

The effect of amorphous (am-), monoclinic (m-), and tetragonal (t-) ZrO2 phase on the physicochemical and catalytic properties of supported Cu catalysts for ethanol conversion was studied. The electronic parameters of Cu/ZrO2 were determined by in situ XAS, and the surface properties of Cu/ZrO2 were defined by XPS and DRIFTS of CO-adsorbed. The results demonstrated that the kind of ZrO2 phase plays a key role in the determination of structure and catalytic properties of Cu/ZrO 2 catalysts predetermined by the interface at Cu/ZrO2. The electron transfer between support and Cu surface, caused by the oxygen vacancies at m-ZrO2 and am-ZrO2, is responsible for the active sites for acetaldehyde and ethyl acetate formation. The highest selectivity to ethyl acetate for Cu/m-ZrO2 catalyst up to 513 K was caused by the optimal ratio of Cu0/Cu+ species and the high density of basic sites (O2-) associated with the oxygen mobility from the bulk m-ZrO2. © 2013 Elsevier Inc. All rights reserved.

Lead-free BaBi4Ti4O15 ceramics: Effect of synthesis methods on phase formation and electrical properties

The processing of ferroelectric BaBi4Ti4O15 (BBT) ceramics from powders prepared by conventional solid state reaction (SSR) and mechanochemical activation (MA) has been investigated. It was shown that MA synthesis reduces the synthesis temperature of BBT powders, leading to smaller particles with reduced anisotropy and consequently to smaller grain size of ceramics. Dielectric properties were investigated in a wide range of temperatures (20-800 degrees C) and frequencies (1.21 kHz to 1 MHz). The relative dielectric permittivity at Curie temperature was higher for solid state obtained ceramics than for the mechanically treated ones. The conductivity of sintered samples was studied, suggesting decreasing of conductivity of BBT-MA in comparison with BBT-SS ceramics. The influence of the grain and the grain boundaries contribution to the dielectric behavior in both ceramics was analyzed through impedance spectroscopy. A well-defined ferroelectric hysteresis loop was obtained for both samples. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Effect of surface and heat treatments on the biaxial flexural strength and phase transformation of a Y-TZP ceramic

To evaluate the effect of grinding and airborne-particle abrasion on the biaxial flexural strength (BFS) and phase transformation of a Y-TZP ceramic, and examine whether sintering the veneering porcelain renders the previous heat treatment recommended by the manufacturer unnecessary. Materials and Methods: Lava zirconia specimens (N = 108) were obtained with the following dimensions: 14.0 mm diameter × 1.3 mm thickness (n = 36) and 14.0 mm × 1.6 mm (n = 72). The thicker specimens were ground with diamond burs under irrigation and received (heat-treated groups) or not (non-heat-treated groups) a heat treatment (1000°C for 30 min) prior to the four firing cycles applied to simulate the sintering of the veneering porcelain. All specimens were air abraded as follows (n = 12): 1) 30-μm silica-modified Al2O3 particles (Rocatec Soft); 2) 110-μm silica-modified Al2O3 particles (Rocatec Plus); and 3) 120-μm Al2O3 particles, followed by Rocatec Plus. Three specimens of each group were analyzed by x-ray diffraction (XRD) to assess the monoclinic phase content (%). The BFS test was performed in a mechanical testing machine (Instron 8874). Data (MPa) were analyzed by two-way ANOVA (grinding × airborne-particle abrasion and heat treatment × airborne-particle abrasion) and Tukey's post-hoc test (α = 0.05). The strength reliability was analyzed using the Weibull distribution. Results: Grinding significantly decreased the BFS of the non-heat-treated groups (p < 0.01). Within the ground groups, the previous heat treatment did not influence the BFS (p > 0.05). Air abrasion only influenced the BFS of the ground/heat-treated groups (p < 0.01). For the non-heat-treated groups, the grinding did not decrease the Weibull modulus (m), but it did decrease the characteristic strength (σ0). For Rocatec Soft and 120-μm Al2O3 particles + Rocatec Plus, the heat-treated groups presented lower m and higher σ0 than the ground/non-heat-treated groups. The independent variables did not seem to influence phase transformation. Air-abraded surfaces presented higher monoclinic zirconia content than the as-sintered and ground surfaces, which exhibited similar content. Conclusion: Even under irrigation, grinding compromised the Y-TZP ceramic strength. The sintering of the veneering porcelain rendered the previous heat treatment recommended by the manufacturer unnecessary. Airborneparticle abrasion influenced the strength of heat-treated zirconia.

Effect of surface and heat treatments on the biaxial flexural strength and phase transformation of a y-tzp ceramic

To evaluate the effect of grinding and airborne-particle abrasion on the biaxial flexural strength (BFS) and phase transformation of a Y-TZP ceramic, and examine whether sintering the veneering porcelain renders the previous heat treatment recommended by the manufacturer unnecessary. Materials and Methods: Lava zirconia specimens (N = 108) were obtained with the following dimensions: 14.0 mm diameter × 1.3 mm thickness (n = 36) and 14.0 mm × 1.6 mm (n = 72). The thicker specimens were ground with diamond burs under irrigation and received (heat-treated groups) or not (non-heat-treated groups) a heat treatment (1000°C for 30 min) prior to the four firing cycles applied to simulate the sintering of the veneering porcelain. All specimens were air abraded as follows (n = 12): 1) 30-μm silica-modified Al2O3 particles (Rocatec Soft); 2) 110-μm silica-modified Al2O3 particles (Rocatec Plus); and 3) 120-μm Al2O3 particles, followed by Rocatec Plus. Three specimens of each group were analyzed by x-ray diffraction (XRD) to assess the monoclinic phase content (%). The BFS test was performed in a mechanical testing machine (Instron 8874). Data (MPa) were analyzed by two-way ANOVA (grinding × airborne-particle abrasion and heat treatment × airborne-particle abrasion) and Tukey's post-hoc test (α = 0.05). The strength reliability was analyzed using the Weibull distribution. Results: Grinding significantly decreased the BFS of the non-heat-treated groups (p < 0.01). Within the ground groups, the previous heat treatment did not influence the BFS (p > 0.05). Air abrasion only influenced the BFS of the ground/heat-treated groups (p < 0.01). For the non-heat-treated groups, the grinding did not decrease the Weibull modulus (m), but it did decrease the characteristic strength (σ0). For Rocatec Soft and 120-μm Al2O3 particles + Rocatec Plus, the heat-treated groups presented lower m and higher σ0 than the ground/non-heat-treated groups. The independent variables did not seem to influence phase transformation. Air-abraded surfaces presented higher monoclinic zirconia content than the as-sintered and ground surfaces, which exhibited similar content. Conclusion: Even under irrigation, grinding compromised the Y-TZP ceramic strength. The sintering of the veneering porcelain rendered the previous heat treatment recommended by the manufacturer unnecessary. Airborneparticle abrasion influenced the strength of heat-treated zirconia.

Effect of particle size on the flexural strength and phase transformation of an airborne-particle abraded yttria-stabilized tetragonal zirconia polycrystal ceramic.

Statement of problem Because airborne-particle abrasion is an efficient method of improving the bond at the zirconia-cement interface, understanding its effect on the strength of yttria-stabilized tetragonal zirconia polycrystal is important. Purpose The purpose of this study was to evaluate the effect of the particle size used for airborne-particle abrasion on the flexural strength and phase transformation of a commercially available yttria-stabilized tetragonal zirconia polycrystal ceramic. Material and Methods For both flexural strength (20.0 × 4.0 × 1.2 mm) (n=14) and phase transformation (14.0-mm diameter × 1.3-mm thickness) (n=4), the zirconia specimens were made from Lava, and their surfaces were treated in the following ways: as-sintered (control); with 50-μm aluminum oxide (Al2O3) particles; with 120-μm Al2O3 particles; with 250-μm Al2O3 particles; with 30-μm silica-modified Al2O3 particles (Cojet Sand); with 120-μm Al2O3 particles, followed by 110-μm silica-modified Al2O3 particles (Rocatec Plus); and with Rocatec Plus. The phase transformation (%) was assessed by x-ray diffraction analysis. The 3-point flexural strength test was conducted in artificial saliva at 37°C in a mechanical testing machine. The data were analyzed by 1-way ANOVA and the Tukey honestly significant difference post hoc test (α=.05). Results Except for the Cojet Sand group, which exhibited statistically similar flexural strength to that of the as-sintered group and for the group abraded with 250-μm Al2O3 particles, which presented the lowest strength, airborne-particle abrasion with the other particle sizes provided the highest values, with no significant difference among them. The as-sintered specimens presented no monoclinic phase. The groups abraded with smaller particles (30 μm and 50 μm) and those treated with the larger ones (110 μm and/or 120 μm particles and 250 μm) exhibited percentages of monoclinic phase that varied from 4% to 5% and from 8.7% to 10%. Conclusions Except for abrasion with Cojet Sand, depending on the particle size, zirconia exhibited an increase or a decrease in its flexural strength. Airborne-particle abrasion promoted phase transformation (tetragonal to monoclinic), and the percentage of monoclinic phase varied according to the particle size.

Effect of humidity and solvent vapor phase on cellulose esters films

In the present study the effect of relative humidity (RH) during spin-coating process on the structural characteristics of cellulose acetate (CA), cellulose acetate phthalate (C-A-P), cellulose acetate butyrate (CAB) and carboxymethyl cellulose acetate butyrate (CMCAB) films was investigated by means of atomic force microscopy (AFM), ellipsometry and contact angle measurements. All polymer solutions were prepared in tetrahydrofuran (THF), which is a good solvent for all cellulose esters, and used for spin-coating at RH of (35 +/- A 5)%, (55 +/- A 5)% or (75 +/- A 5)%. The structural features were correlated with the molecular characteristics of each cellulose ester and with the balance between surface energies of water and THF and interface energy between water and THF. CA, CAB, CMCAB and C-A-P films spin-coated at RH of (55 +/- A 5)% were exposed to THF vapor during 3, 6, 9, 60 and 720 min. The structural changes on the cellulose esters films due to THF vapor exposition were monitored by means of AFM and ellipsometry. THF vapor enabled the mobility of cellulose esters chains, causing considerable changes in the film morphology. In the case of CA films, which are thermodynamically unstable, dewetting was observed after 6 min exposure to THF vapor. On the other hand, porous structures observed for C-A-P, CAB and CMCAB turned smooth and homogeneous after only 3 min exposure to THF vapor.

Effect of alkyl chain length of alcohols on nematic uniaxial-to-biaxial phase transitions in a potassium laurate/alcohol/K2SO4/water lyotropic mixture

Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K2SO4)/alcohol (n-OH)/water, with the alcohols having different numbers of carbon atoms in the alkyl chain (n), from 1-octanol to 1-hexadecanol, were investigated by optical techniques (optical microscopy and laser conoscopy). The biaxial nematic phase domain is present in a window of values of n = n(KL) +/- 2, where n(KL) = 11 is the number of carbon atoms in the alkyl chain of KL. The biaxial phase domain became smaller and the uniaxial-to-biaxial phase transition temperatures shifted to relatively higher temperatures upon going from 1-nonanol to 1-tridecanol. Moreover, compared with other lyotropic mixtures these new mixtures present high birefringence values, which we expect to be related to the micellar shape anisotropy. Our results are interpreted assuming that alcohol molecules tend to segregate in the micelles in a way that depends on the relative value of n with respect to nKL. The larger the value of n, the more alcohol molecules tend to be located in the curved parts of the micelle, favoring the uniaxial nematic calamitic phase with respect to the biaxial and uniaxial discotic nematic phases.