Effect of tetragonal distortion on ferroelectric domain switching: A case study on La-doped BiFeO3-PbTiO3 ceramics

The ferroelectric and piezoelectric properties of (1-x)BiFeO3-xPbTiO(3) (BF-PT) ceramics were investigated as a function of tetragonal distortion. The latter was adjusted by employing La-doping (0-30 at %) while keeping the material near the morphotropic phase boundary by varying x between 0.35 and 0.46. This allows changing the c/a ratio of tetragonal BF-PT in the range from 1.10-1.01 and consequently alters the level of compatibility stresses. It was found that the c/a ratio has a significant influence on domain switching as inferred from electric field induced polarization, strain hysteresis, and Rayleigh measurements. Specifically, a threshold c/a ratio of about 1.045 was identified below which the electric field induced domain mobility increases sharply.open342

Prediction of human drug-induced liver injury (DILI) in relation to oral doses and blood concentrations

Drug-induced liver injury (DILI) cannot be accurately predicted by animal models. In addition, currently available in vitro methods do not allow for the estimation of hepatotoxic doses or the determination of an acceptable daily intake (ADI). To overcome this limitation, an in vitro/in silico method was established that predicts the risk of human DILI in relation to oral doses and blood concentrations. This method can be used to estimate DILI risk if the maximal blood concentration (Cmax) of the test compound is known. Moreover, an ADI can be estimated even for compounds without information on blood concentrations. To systematically optimize the in vitro system, two novel test performance metrics were introduced, the toxicity separation index (TSI) which quantifies how well a test differentiates between hepatotoxic and non-hepatotoxic compounds, and the toxicity estimation index (TEI) which measures how well hepatotoxic blood concentrations in vivo can be estimated. In vitro test performance was optimized for a training set of 28 compounds, based on TSI and TEI, demonstrating that (1) concentrations where cytotoxicity first becomes evident in vitro (EC10) yielded better metrics than higher toxicity thresholds (EC50); (2) compound incubation for 48 h was better than 24 h, with no further improvement of TSI after 7 days incubation; (3) metrics were moderately improved by adding gene expression to the test battery; (4) evaluation of pharmacokinetic parameters demonstrated that total blood compound concentrations and the 95%-population-based percentile of Cmax were best suited to estimate human toxicity. With a support vector machine-based classifier, using EC10 and Cmax as variables, the cross-validated sensitivity, specificity and accuracy for hepatotoxicity prediction were 100, 88 and 93%, respectively. Concentrations in the culture medium allowed extrapolation to blood concentrations in vivo that are associated with a specific probability of hepatotoxicity and the corresponding oral doses were obtained by reverse modeling. Application of this in vitro/in silico method to the rat hepatotoxicant pulegone resulted in an ADI that was similar to values previously established based on animal experiments. In conclusion, the proposed method links oral doses and blood concentrations of test compounds to the probability of hepatotoxicity

Herstellung und Schaltverhalten neuer bismuthaltiger Hochtemperaturpiezokeramiken

Zur Untersuchung des Einflusses der tetragonalen Verzerrung auf das Schaltverhalten von Ferroelektrika wurden lanthandotierte Bismutferrit-Bleititanat-Piezokeramiken (BF-PT) mit einer tetragonalen Verzerrung zwischen 1,10 und 1,01 hergestellt und elektrisch, mechanisch und strukturell charakterisiert. Dies schloss temperaturabhängige Messungen der Struktur, der dielektrischen Permittivität und des piezoelektrischen Koeffizienten ein. Die Messungen zeigten, dass die Tetragonalität der Kristallstruktur einen erheblichen Einfluss auf die Eigenschaften von BF-PT hat. Es konnte ein Schwellenwert bei 1,045 nachgewiesen werden, oberhalb dessen Domänenschalten fast vollständig unterdrückt ist. Dieser Schwellenwert wurde über Rayleighmessungen sowie Röntgen- und Neutronenbeugungsmessungen bestätigt. Er besitzt sowohl für rein elektrische als auch für rein mechanische Belastung Gültigkeit

On cracks and delaminations of thermal barrier coatings due to indentation testing: Experimental investigations

Rockwell indentation testing as a method of establishing the interfacial fracture toughness of thermal barrier coatings is investigated. To this end, indentation tests have been systematically performed on coatings with yttria-stabilized zirconia top coat deposited by electron beam physical vapor deposition. Specimens in ‘‘as-coated” condition and after heat treatment in air have been studied. Unexpectedly, indentation of the heat-treated samples resulted in smaller delaminations than the as-coated samples, suggesting an increase in fracture toughness for coatings subjected to elevated temperatures. Careful image analyses of the cross-section of the indented area show that the ceramic top coat undergoes a complex damage evolution during indentation that is altered by thermal treatment. The consequences of this are discussed and we note that care must be taken when evaluating fracture parameters for multilayered structures based on indentation testing

Shift in Morphotropic Phase Boundary in La-Doped BiFeO3-PbTiO3 Piezoceramics

Polycrystalline BiFeO3-PbTiO3 (BF-PT) powders with mixed tetragonal and rhombohedral crystal structure (morphotropic phase boundary: MPB) were modified with lanthanum to provide a wide variation in tetragonal distortion. X-ray diffraction from both the powder and the corresponding bulk ceramic demonstrated that the MPB in the bulk is shifted from 1-5mol% towards the tetragonal PT as compared to the powder. This shift was correlated with the degree of tetragonal distortion as quantified by c/a ratio.close141

Crack growth resistance behavior of lanthanum doped bismuth ferrite–lead titanate: Effect of tetragonality and mixed phase crystal structures

The room temperature crack growth resistance behavior of polycrystalline lanthanum-doped bismuth ferrite-lead titanate was characterized with disc compact-tension specimens. Through lanthanum doping the tetragonality can be adjusted from 1.01 to 1.10, while retaining a mixed phase system. Experimental measurements show changes in toughening behavior with increasing c/a ratio. Fracture results are discussed in conjunction with macroscopic ferroelastic constitutive behavior and stress-dependent neutron diffraction measurements to elucidate the role of a mixed phase system with heterogeneous mechanical properties. Additional X-ray diffraction measurements were performed to determine the effect of possible crack-tip stress-induced phase transformations on R-curve behavior

Ferroelectric properties of lead zirconate titanate under radial load

Ferroelectric and ferroelastic properties are closely entwined in piezoelectric perovskites. Research on this topic has been mostly limited to collinear action of electric field and mechanical load. Here, the effect of a radial mechanical load and an axial electric field applied simultaneously to a cylindrical lead zirconate titanate sample is investigated. The dielectric constant after poling under load indicates that domain wall movement is facilitated, while the number of domain walls is reduced. Hysteresis measurements show that the remnant polarization and coercive field depend characteristically on the load, with a clear behavior change at the ferroelastic coercive stress. (c) 2007 American Institute of Physics

Evaluation of the Rockwell indentation test for interfacial fracture toughness measurement of Thermal Barrier Coating systems

A critical measure of the adherence of a Thermal Barrier Coating (TBC) to the substrate is its interfacial fracture toughness. Indentation testing has been proposed by several authors as a method for estimating the interfacial fracture toughness of TBC systems: indentation perpendicular to the surface generates local coating debonding, which size can be used for calculating the interfacial fracture toughness. This test has several striking advantages: it is easy to perform, small quantity of material is necessary, elaborate sample preparation is not required, and the test can be applied on components. The drawback is the difficult interpretation of the test results, which are sometimes misleading. In this study, instrumented Rockwell indentation tests have systematically been performed on TBC systems with the ceramic top coat deposited by electron beam physical vapor deposition. Specimens in “as coated” condition and after different heat treatments, which impair the interfacial fracture toughness, have been investigated. The damages induced in the TBC system during the indentation process have been analyzed by microscopic investigation of cross sections after testing with different maximum loads. It was found that crushing and compaction of the brittle TBC, crack initiation within the TBC, and deformation of the substrate are controlling the formation of debonding cracks. The experimental results are discussed in terms of energy consumption for the observed damage processes and driving force for the evolution of debonding cracks

Piezoelectric activity of (1-x)[0.35Bi(Mg1/2Ti1/2)O-3-0.3BiFeO(3)-0.35BiScO(3)] - xPbTiO(3) ceramics as a function of temperature

The piezoelectric and ferroelectric properties of ceramics in the (1-x)[0.35Bi(Mg1/2Ti1/2)O-3-0.3BiFeO(3)-0.35BiScO(3)] - xPbTiO(3) (0.46 a parts per thousand currency signaEuro parts per thousand x a parts per thousand currency signaEuro parts per thousand 0.50) solid solution have been studied as a function of temperature with a view to establishing their potential for commercial usage as high T-C actuators and sensors. The polarisation, unipolar and bipolar strain, piezoelectric coefficient d(33) and coupling factor k(p) all increased with temperature consistent with softening of extrinsic and intrinsic contributions to piezoactivity as T-C is approached. Small signal d(33) and k(p) increased from 328 pm/V and similar to 0.45 at room temperature to > 1100 pm/V and similar to 0.5, respectively, until depoling occurred at similar to 400A degrees C, illustrating a significant improvement in operating temperature over PZT (similar to 200A degrees C) and demonstrating great potential for high temperature sensor applications. Bipolar (bi) and unipolar (uni) measurements (large signal, d(*) (33)) normally used to demonstrate potential for actuation, revealed extremely promising values, d(*) (33(bi)) = 940 pm/V and d(*) (33(uni)) = 600 pm/V, up to 180A degrees C, the limit of the experimental apparatus.close7