Two-dimensional mapping of triaxial strain fields in a multiferroic BiFeO3 thin film using scanning x-ray microdiffraction

The dramatically enhanced polarizations and saturation magnetizations observed in the epitaxially constrained BiFeO3 (BFO) thin films with their pronounced grain-orientation dependence have attracted much attention and are attributed largely to the constrained in-plane strain. Thus, it is highly desirable to directly obtain information on the two-dimensional (2D) distribution of the in-plane strain and its correlation with the grain orientation of each corresponding microregion. Here the authors report a 2D quantitative mapping of the grain orientation and the local triaxial strain field in a 250 nm thick multiferroic BFO film using a synchrotron x-ray microdiffraction technique. This direct scanning measurement demonstrates that the deviatoric component of the in-plane strain tensor is between 5x10(-3) and 6x10(-3) and that the local triaxial strain is fairly well correlated with the grain orientation in that particular region. (c) 2007 American Institute of Physics.X1145Nsciescopu

Large enhancement of the photovoltaic effect in ferroelectric complex oxides through bandgap reduction

Tuning the bandgap in ferroelectric complex oxides is a possible route for improving the photovoltaic activity of materials. Here, we report the realization of this effect in epitaxial thin films of the ferroelectric complex oxide Bi3.25La0.75Ti3O12 (BLT) suitably doped by Fe and Co. Our study shows that Co (BLCT) doping and combined Fe, Co (BLFCT) doping lead to a reduction of the bandgap by more than 1 eV compared to undoped BLT, accompanied by a surprisingly more efficient visible light absorption. Both BLCT and BLFCT films can absorb visible light with a wavelength of up to 500 nm while still exhibiting ferroelectricity, whereas undoped BLT only absorbs UV light with a wavelength of less than 350 nm. Correlated with its bandgap reduction, the BLFCT film shows a photocurrent density enhanced by 25 times compared to that of BLT films. Density functional theory calculations indicate that the bandgap contraction is caused by the formation of new energy states below the conduction bands due to intermixed transition metal dopants (Fe, Co) in BLT. This mechanism of tuning the bandgap by simple doping can be applied to other wide-bandgap complex oxides, thereby enabling their use in solar energy conversion or optoelectronic applications

Bone dynamics in the upward direction after a maxillary sinus floor elevation procedure: serial segmentation using synchrotron radiation micro-computed tomography

Seung-Jun Seo,1,* Chung Wung Bark,2,* Jae-Hong Lim,1 Yong-Gun Kim3 1Industrial Technology Convergence Center, Pohang Accelerator Laboratory, POSTECH, Pohang, Gyeongbuk, 2Department of Electrical Engineering, Gachon University, Seongnam, 3Department of Periodontology, School of Dentistry, Kyungpook National University, Daegu, Republic of Korea *These authors contributed equally to this work Objective: Maxillary sinus floor augmentation has been shown to be the most predictable surgical technique for enhancing the bone volume in the posterior area of the maxilla. The purpose of this study was to analyze the serial slice image segmentation of newly formed bone and bone substitutes after sinus floor elevation using synchrotron radiation X-ray micro-computed tomography (SR-µCT).Materials and methods: Bone biopsy specimens were collected after 6 months of sinus floor augmentation. From the six bone biopsy specimens, the cross-sectional images at every 8 µm along the apical direction from the inferior border using serial segmentation from three-dimensional reconstructed X-ray images were analyzed. The amount of new bone and bone substitutes were measured at each slicing image (300–430 images per specimen).Results: The bone dynamics between the new bone and bone substitutes along the inferior–superior direction in humans after maxillary sinus floor elevation (MSFE) were analyzed using the whole sample region. Although these observations suggest that the specimens are structurally inhomogeneous, sinus floor elevation was confirmed to be a reliable surgical procedure for increasing the amount of bone.Conclusion: SR-µCT is highly effective for obtaining high-resolution images. An analysis of biological specimens using SR-µCT is quite reliable and this technique will be an important tool in the wide field of tissue engineering. Keywords: maxillary sinus floor elevation, synchrotron radiation, micro-computed tomography, serial segmentation, new bone formatio

Electric-field-induced structural modulation of epitaxial BiFeO3 multiferroic thin films as studied using X-ray microdiffraction

An in situ method, called synchrotron x-ray microdiffraction, was introduced to examine the electric-field-induced structural modulation of the epitaxially grown pseudotetragonal BiFeO3 thin film. To evaluate the d spacing (d(001)) from the measured intensity contour in the 2 theta-chi space, the peak position in each diffraction profile was determined by applying two-dimensional Lorentzian fitting. By tracing the change of d spacing as a function of the applied electric field and by examining the Landau free energy function for P4mm symmetry, the authors were able to estimate the two important parameters that characterize the field-induced structural modulation. The estimated linear piezoelectric coefficient (d(33)) at zero-field limit is 15 pm/V, and the effective nonlinear electrostrictive coefficient (Q(eff)) is as low as similar to 8.0x10(-3) m(4)/C-2. (c) 2007 American Institute of Physics.X112022sciescopu

R3c-R3m Octahedron-tilting Transition in Rhombohedrally-distorted BiFeO3 Multiferroics

Multiferroic BiFeO3 (BFO) with the rhombohedral R3c symmetry is characterized by a clockwise-counterclockwise tilting (theta) of the FeO6 octahedron unit along the threefold pseudo-cubic [111](c) direction. A phase transition associated with the disappearance of theta is conceivable at a high temperature as thermal energy tends to break up this antiferro-distortive ordering network along the [111](c) direction. Based on a high-resolution synchrotron X-ray diffraction study, we have found that the R3c BFO undergoes a transition to the R3m symmetry (with theta = 0) at similar to 530 K, which is substantially lower than the antiferro-to-paramagnetic transition temperature of 643 K. The energy lowering caused by an antiferrodistortive R3c pairing is estimated to be 0.28 eV per unit cell.X1124sciescopuskc

Microdiffraction study of polycrystalline copper during uniaxial tension deformation using a synchrotron x-ray source

In-situ measurement of local orientation and strain Has Been carried out for a copper-polycrystals under a uniaxial loading using a synchrotron x-ray microdiffraction method at the Advanced Light Source. The heterogeneities of deformation-induced microstructure within single grains were observed. There were differences in the selection of simultaneously acting slip systems among neighboring volume elements within a grain.X11sciescopu

Formation of dark spots induced by crystallization of organic layers in organic light-emitting diodes

We report electroluminescence degradation in organic light emitting diode as a function of applying bias. A number of dark spots were produced as applying bias increased. Microscope image showed that dark spots are related to many protrusions and hollows formed on Al electrode. X-ray diffraction and x-ray micro-diffraction indicate that Joule heat from high electric field induced the crystallization of organic materials, forming dark spots via peeling-off the Al cathode from Alq3 layers.11Nsciescopu

Variations of ferroelectric off-centering distortion and 3d-4p orbital mixing in La-doped BiFeO3 multiferroics

The lanthanum (La) modification is known to improve dielectric and magnetic properties of BiFeO3 (BFO), a promising room-temperature multiferroic oxide. The effects of La doping on the variations of the off-centering distortion and the orbital mixing of BFO are experimentally studied, in conjunction with first-principles density-functional theory (DFT) calculations. Both the Fe-O bond anisotropy in the FeO6-octahedron cage and the off-centering ferroelectric polarization along the hexagonal [001](h) h are predicted to be substantially reduced by the La doping. These DFT predictions agree with the structural-refinement results obtained from high-resolution x-ray powder-diffraction data. We have shown that the apparent improvement of the polarization-field response is not intrinsic and can be attributed to the reduced leakage current by the La doping. X-ray absorption near-edge structure (XANES) spectroscopy study further indicates that the degree of Fe 3d-4p orbital mixing decreases with the La doping. The conclusion deduced from XANES study correlates well with the orbital-resolved density of states which predicts that the La doping increases the number of unoccupied states in the p orbital but suppresses the number of unoccupied states in the Fe 3d orbital.open115963sciescopu