Correlating phase and microstructure development versus dielectric properties in La and Er co-doped Bi4Ti3O12 ferroelectric ceramics

Bi_3.25La_0.75−xEr_xTi₃O₁₂ and Bi_3.25La_0.75Ti_3−xEr_xO_12−δ ceramics were prepared and studied in this work in terms of dopant-induced phase and microstructure development as well as dielectric response. The results show that introduction of Er³⁺ tends to reduce the materials’ sintering temperature and average grain size. Moreover, it was noted that in these systems the substitution site of this dopant is controlled by valence state and ionic radii mismatch effects. In particular, even when a nominal substitution of Ti⁴⁺ is conceived, here it is found that Er³⁺ also incorporates at the (Bi,La)³⁺ sites. These and other interesting concluding remarks from this work, including Er³⁺ tolerance, were possible only after comparing, especially, the X-ray diffraction results and the intrinsic ferroelectric characteristics extracted from the dielectric measurements.     

Sintering-driven effects on the band gap of (Pb,La)(Ti,Ni)O3 photovoltaic ceramics

In this work, the influence of the sintering temperature on the physical properties of (Pb_0.8La_0.2)(Ti_0.9Ni_0.1)O₃ (PLT-Ni) ceramics is reported. The experimental data revealed that the energy band gap of PLT-Ni ceramics could be tailored from approximately 2.7 to 2.0 eV by changing the sintering temperature from 1100°C to 1250°C. It is demonstrated that the simple substitution of Ti⁴⁺ by Ni²⁺ cations is effective to decrease the intrinsic band gap while increasing the tetragonality factor and the spontaneous polarization. However, the additional red-shift observed in the absorption edge of the PLT-Ni with increasing the sintering temperature was associated with a continuous increase in the oxygen vacancies () amount. It is believed that the impact of the creation of these thermally induced is manifold. The presence of and Ni²⁺ ions generate the Ni²⁺- defect-pairs that promoted both a decrease in the intrinsic band gap and an additional increase of the tetragonality factor, consequently, increasing the spontaneous polarization. The creation of Ni²⁺- defects also changed the local symmetry of Ni²⁺ ions from octahedral to a square pyramid, thus lifting the degeneracy of the Ni²⁺ 3d orbitals. With the increase in the sintering temperature, lower-energy absorbing intraband states were also formed due to an excess of , being responsible for an add-on shoulder in the absorption edge, extending the light absorption curve to longer wavelengths and leading to an additional absorption in “all investigated” spectrum as well.     

Local electronic structure,optical bandgap and photoluminescence (PL) properties of Ba(Zr0.75Ti0.25)O3 powders

Ba(Zr_0.75Ti_0.25)O₃ (BZT-75/25) powders were synthesized by the polymeric precursor method. Samples were structurally characterized by X-ray diffraction (XRD), Rietveld refinement, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) techniques. Their electronic structures were evaluated by first-principle quantum mechanical calculations based on density functional theory at the B3LYP level. Their optical properties were investigated by ultraviolet-visible (UV-Vis) spectroscopy and photoluminescence (PL) measurements at room temperature. XRD patterns and Rietveld refinement data indicate that the samples have a cubic structure. XANES spectra confirm the presence of pyramidal [TiO₅] clusters and octahedral [TiO₆] clusters in the disordered BZT-75/25 powders. EXAFS spectra indicate distortion of Ti–O and Ti–O–Ti bonds the first and second coordination shells, respectively. UV-Vis absorption spectra confirm the presence of different optical bandgap values and the band structure indicates an indirect bandgap for this material. The density of states demonstrates that intermediate energy levels occur between the valence band (VB) and the conduction band (CB). These electronic levels are due to the predominance of 4d orbitals of Zr atoms in relation to 3d orbitals of Ti atoms in the CB, while the VB is dominated by 2p orbitals related to O atoms. There was good correlation between the experimental and theoretical optical bandgap values. When excited at 482 nm at room temperature, BZT-75/25 powder treated at 500 °C for 2 h exhibited broad and intense PL emission with a maximum at 578 nm in the yellow region.     

Cerebrospinal fluid fistula: detection with MR cisternography

PURPOSE: Our goal was to assess the role of MR cisternography in the examination of patients with suspected CSF rhinorrhea. METHODS: MR cisternography was performed as a heavily T2-weighted fast spin-echo study with fat suppression and video reversal of the images in 37 patients over a 3-year interval. Twenty-four of the patients subsequently had exploratory surgery for fistula. Statistical analysis of the surgical results was compared with the findings at MR cisternography. RESULTS: MR cisternography showed significant correlation with surgical findings, with sensitivity, specificity, and accuracy of 0.87, 0.57, and 0.78, respectively. CONCLUSION: MR cisternography proved to be an accurate diagnostic imaging technique in the evaluation of suspected CSF rhinorrhea.     

Persistent acute renal failure with renal artery stenosis: cure following reconstructive arterial operation

A case of acute renal failure is reported in which renal function returned after surgical correction of renal artery stenosis to the sole functioning kidney. Acute renal failure associated with renal vascular lesions is reviewed. Although often clinically apparent vascular obstruction may be asymptomatic and should be considered in cases of prolonged acute renal failure.     

Terminal (1)(q43) long-arm deletion of chromosome no. 1 in a three-year-old female

A 3-year-old Latin female is reported with a terminal deletion of the No. 1 chromosome, karyotype formula 46, XX, del(1) (q43). Principle clinical features include: Anatomic - microcephaly; bilateral, convergent strabismus; epicanthus; brachycephaly; bulbar nose; sparse hair; partial soft tissue syndactylism between 2nd and 3rd fingers which are slightly tapered; whorls on all 10 fingers; mild prognathism; solitary kidney; vaginal stenosis; vesicoureteral reflux; asymmetric feet; and subluxation of peroneal tendons around the fibula with severe pronation and heal valgus deformity. Neurologic - moderate motor and mental retardation; high-pitched, shrill cry; absent pincer grasp at 3 years; and grand mal seizures documented from 9 months of age.     

Laser-annealed deep contacts for layered structures

This work is concerned with the preparation of deep contacts for layered structures on GaAs and InP substrates. The advantages of laser technology suggested contact preparation by laser annealing. Results of laser technology optimization are reported and the procedure for contact preparation is described. Concrete deep contacts were produced on structures with a cap layer up to 250 nm thick. This revised version was published online in July 2006 with corrections to the Cover Date.     

Selective regulation of apoptosis: the cytotoxic lymphocyte serpin proteinase inhibitor 9 protects against granzyme B-mediated apoptosis without perturbing the Fas cell death pathway

Cytotoxic lymphocytes (CLs) induce caspase activation and apoptosis of target cells either through Fas activation or through release of granule cytotoxins, particularly granzyme B. CLs themselves resist granule-mediated apoptosis but are eventually cleared via Fas-mediated apoptosis. Here we show that the CL cytoplasmic serpin proteinase inhibitor 9 (PI-9) can protect transfected cells against apoptosis induced by either purified granzyme B and perforin or intact CLs. A PI-9 P1 mutant (Glu to Asp) is a 100-fold-less-efficient granzyme B inhibitor that no longer protects against granzyme B-mediated apoptosis. PI-9 is highly specific for granzyme B because it does not inhibit eight of the nine caspases tested or protect transfected cells against Fas-mediated apoptosis. In contrast, the P1(Asp) mutant is an effective caspase inhibitor that protects against Fas-mediated apoptosis. We propose that PI-9 shields CLs specifically against misdirected granzyme B to prevent autolysis or fratricide, but it does not interfere with homeostatic deletion via Fas-mediated apoptosis.