Search results for "Strontium"
showing 10 items of 195 documents
Dielectric investigation of lead‐free perovskite strontium titanate with 25% bismuth ceramics
2009
In this work lead-free 0.75SrTiO3-0.25BiTiO3 ceramics have been investigated in broad frequency range. Obtained results showed pronounced dispersion below room temperature typical for the dipolar glasses. The calculated relaxation time distribution function broadens toward longest relaxation times part on cooling. The obtained most probable relaxation time diverges according to the Vogel-Fulcher relationship with the following parameters: dipole activation energy EA=2123 K, glassy state temperature T0=52.7 K, shortest relaxation time, referring to dipole relaxations at very high temperatures, τ0=2.1·10–14 s. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Critical Exponents and Randomness in SrTiO3 : Ca
1994
Since its discovery, the SrTiO3: Ca system is known to exhibit a number of features which were thought to arise from an impurity induced disorder. Non-linear dielectric measurements are used to obtain a more quantitative insight into this disorder. For 0.001 < xCa < 0.05, it is found that the non-linear susceptibility diverges at low temperatures. This is similar to what was previously reported in the dielectric random system KTaO3: Na. A method is proposed to quantify the contribution of the disorder to the non-linearities. It is found that the deviation from a true ferroelectric behaviour is not enough to call the low-temperature phase of SrTiO3: Ca a glass one. The maximum non-linearity …
Domain wall splitting and creation of the fine domain structure
1998
Abstract The study of the movement of the paraelectric-ferroelectric interphase boundary in (Ba,Sr)TiO 3 with concentration change is provided in the framework of the mean-field theory. The analytical solution for the parameters of motion of the interphase boundary is applied to the calculations of the splitting of domain walls in (Ba,Sr)TiO 3 for different concentrations of Sr. The calculations are based on the experimental data for the Curie–Weiss constant and for the parameters of the Landau–Ginzburg expression for the free energy.
Comparative study of [001] surface relaxations of perovskite titanates
1998
Surface relaxations of the cubic perovskite SrTiO and BaTiO crystals have been studied in the framework of the shell model. The 33 positions of atoms in several surface layers embedded into the electrostatic field of the remainder of the crystal were calculated. Ti 4q , Sr 2q ,B a 2q and O 2y ions in six near-surface layers are displaced differently from their crystalline sites. Such effects create the so-called surface rumpling, a dipole moment and the electric field in the near-surface region. Calculated atomic displacements were compared with the LEED experimental data and showed good agreement. Our simulations have demonstrated that the cubic perovskite SrTiO crystals 3 reveal surface p…
Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3
2011
Yttrium-doped barium zirconate (BZY) is the most promising candidate for proton-conducting ceramics and has been extensively studied in recent years. The detailed features of the crystal structure, both short-range and long-range, as well as the crystal chemistry driving the doping process, are largely unknown. We use very high resolution X-ray diffraction (HR-XRD) to resolve the crystal structure, which is very slightly tetragonally distorted in BZY, while the local environment around Zr4+ and Y3+ is probed with extended X-ray absorption fine structure (EXAFS), and the symmetry and vibrations are investigated by using Raman spectroscopy. It is found that barium zirconate shows some degree …
Ultratrace analysis and isotope ratio measurements of long-lived radioisotopes by resonance ionization mass spectrometry (RIMS).
2003
Resonance Ionization Mass Spectrometry (RIMS) is a sensitive and selective method for ultratrace analysis of long-lived radioisotopes and isotope ratio measurements. It provides extremely high isobaric suppression and good overall efficiency. The experimental limits of detection are as low as 10(6) atoms per sample and isotopic selectivities of 5x10(12) have been obtained. The widespread potential of RIMS, using different experimental arrangements, is demonstrated for the determination of the radiotoxic isotopes Pu-238 to Pu-244 and Sr-89/Sr-90 in various environmental samples as well as for Ca-41 in nuclear reactor components and biomedical samples.
Fast, low-level detection of strontium-90 and strontium-89 in environmental samples by collinear resonance ionization spectroscopy
1993
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exc…
X-ray Studies of Debye Temperature of Some ABO 3 Perovskites
2002
Debye temperatures T D of some perovskite compounds are determined by X-ray diffraction. Correlation between T D determined at T=180 °C, mean square displacements of atoms, quasi-elastic coupling, and melting temperature of the perovskite compounds is analysed.
Approaching a “naked” boryl anion: amide metathesis as a route to calcium, strontium, and potassium boryl complexes
2020
Abstract Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me3Si)2N}M{B(NDippCH)2}(thf)n (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe3)2}2(thf)2, with (thf)2Li‐ {B(NDippCH)2}. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe3)2}, leading to the formation of the solvent‐free borylpotassium dimer [K{B(NDippCH)2}]2, which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K+ cations interact weakly with both the ipso‐carbons of the flanki…
Strontium isotopes as tracers of water-rocks interactions, mixing processes and residence time indicator of groundwater within the granite-carbonate …
2016
This study aims at identifying the water-rock interactions and mixing rates within a complex granite-carbonate coastal aquifer under high touristic pressure. Investigations have been carried out within the coastal aquifer of Bonifacio (southern Corsica, France) mainly composed of continental granitic weathering products and marine calcarenite sediments filling a granitic depression. A multi-tracer approach combining physico-chemical parameters, major ions, selected trace elements, stable isotopes of the water molecule and 87Sr/86Sr ratios measurements is undertaken for 20 groundwater samples during the low water period in November 2014. 5 rock samples of the sedimentary deposits and surroun…