Oxides SrO Research Articles

Density functional model of threshold voltage shifts at High-K/Metal gates

A density functional analysis of oxide dipole layers used to set the threshold voltages in high-K/metal CMOS gate stacks is given in terms of the band alignments and chemical trends of these component oxide layers. The oxides SrO, La2O3, HfO2 and Al2O3 are found to have similar band gaps and form a ‘staircase’ of band alignments, allowing them to shift the metal electrode Fermi level in both n-type and p-type directions. This analysis supersedes previous largely empirical models based on metal oxide ion densities or electronegativity scales.

Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma.

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. Using emission spectroscopy acquired after ablation of a SrZrO3 target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO2 are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an 18O2 environment by observing the in-growth of Zr18O in the emission spectra relative to Zr16O, which was formed by reaction of Zr with 16O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Using a simple temperature-dependent reaction model, we have illustrated that the formation sequence of these oxides subsequent to ablation is predictable to first order.

Frontier Orbital Engineering of Metal–Organic Frameworks with Extended Inorganic Connectivity: Porous Alkaline-Earth Oxides

The development of conductive metal-organic frameworks is challenging owing to poor electronic communication between metal clusters and the organic ligands that bridge them. One route to overcoming this bottleneck is to extend the inorganic dimensionality, while using the organic components to provide chemical functionality. Using density functional theory methods, we demonstrate how the properties of the alkaline-earth oxides SrO and BaO are transformed upon formation of porous solids with organic oxygen sources (acetate and trifluoroacetate). The electron affinity is significantly enhanced in the hybrid materials, while the ionization potential can be tuned over a large range with the polarity of the organic moiety. Furthermore, because of their high-vacuum fraction, these materials have dielectric properties suitable for low-κ applications.

Comparative spectral and shielding studies of binary borate glasses with the heavy metal oxides SrO, CdO, BaO, PbO or Bi2O3 before and after gamma irradiation

This work aims to compare the experimental shielding behavior of some prepared binary borate glasses with SrO, CdO, BaO, PbO or Bi2O3 towards successive gamma irradiation by investigating their combined optical and FTIR spectral measurements before and after gamma irradiation. Optical spectra of all the samples reveal strong UV absorption which is related to the presence of unavoidable trace iron impurities (Fe3+ ions) contaminated within the raw materials which were used for the preparation of the studied glasses. Additional near visible bands are observed in the two lead borate and bismuth borate glasses due to characteristic absorption of Pb2+ and Bi3+ ions. Gamma irradiation causes varying responses depending on the type of glass. Bismuth borate glass shows highly marked shielding towards successive gamma irradiation while lead borate glass reveals resistance in low dose (4Mrad) and produces induced defects at high dose (8Mrad). The other glasses show obvious generation of induced defects upon gamma irradiation. FTIR spectra of the glasses reveal vibrational modes characteristic to combined presence of triangular and tetrahedral borate units in their specific different wavenumbers besides the presence of interfering structural PbO and BiO linkages in the lead borate and bismuth borate glasses. Gamma irradiation produces limited changes in the FTIR spectra specifically the intensity of some vibrational modes while the bismuth borate glass has proved to be the best radiation-shielding candidate when comparing the combined spectral results after successive gamma irradiation.

Study of XeF2 fluorination potential against SrO, MoO3, and Nb2O5 in TG/DTA for use in reactive gas recycle

Oxides SrO, MoO3, and Nb2O5, simulating parts of the Used Nuclear Fuel (UNF) matrix were fluorinated using XeF2 to form volatile and non-volatile compounds to demonstrate the possibility of a chemical and thermal separations. Experiments were conducted using a TG/DTA instrument at the milligram quantity scale, and XRD enabled confirmation for the fluorination reaction when sample residues were present. The study of these chemistries could be incorporated into advanced separations methods to provide another possible solution for the long-term, sustainability of nuclear power as the issue of reuse and disposal of commercial fuel continues to grow.

Calcium Ruthenates: Determination of Gibbs Energies of Formation Using Electrochemical Cells.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Oxide nano-engineering using MBE

Molecular beam epitaxy (MBE) has achieved unparalleled control in the integration of semiconductors at the nanometer level; its use for the integration of oxides with similar nanoscale customization appears promising. This paper describes the use of reactive MBE to synthesize layered oxide heterostructures, including new compounds and metastable superlattices, involving monolayer-level integration of the dielectric and ferroelectric oxides SrO, SrTiO 3, BaTiO 3, PbTiO 3, and Bi 4Ti 3O 12. The controlled synthesis of such layered oxide heterostructures offers great potential for tailoring the dielectric and ferroelectric properties of materials. Oxide nano-engineering is accomplished by supplying the incident species in the desired layering sequence with submonolayer composition control. Comparisons between the growth of compound semiconductors and oxides by MBE are made.

Ground-state properties and excitation energies of cubic SrO and MgO

Electronic ground-state properties and quasiparticle energies of the charge-transfer insulating oxides SrO and MgO have been computed. Structural properties calculations have been performed within DFT–LDA, while for the electronic excitations an efficient DFT–GW scheme, founded on the use of a model dielectric function, has been used. The comparison of our results with available theoretical and experimental data turns out to be satisfactory either for the ground state or for the excitation spectrum.

Structural properties and quasiparticle energies of cubic SrO, MgO and SrTiO3

The structural properties and the band structures of the charge-transfer insulating oxides SrO, MgO and SrTiO3 are computed both within density functional theory in the local density approximation (LDA) and in Hedin's GW-scheme for self-energy corrections, by using a model dielectric function, which approximately includes local field and dynamical effects. The deep valence states are shifted by the GW-method to higher binding energies, in very good agreement with photoemission spectra. Since in all of these oxides the direct gaps at high-symmetry points of the Brillouin zone may be very sensitive to the actual value of the lattice parameter a already at the LDA level, self-energy corrections are computed both at the theoretical and the experimental a. For MgO and SrO, the values of the energies of transition between the valence and the conduction bands are improved by GW-corrections, while for SrTiO3 they are overestimated. The results are discussed in relation to the importance of local field effects and to the nature of the electronic states in these insulating oxides.

Study of Ag/La0.6Sr0.4MnO3 catalysts for complete oxidation of methanol and ethanol at low concentrations

Ag-modified La0.6Sr0.4MnO3-based catalysts with the perovskite-type structure were prepared by using a citric acid sol–gel method, and their catalytic performance for complete oxidation of methanol and ethanol was evaluated and compared with that of the γ-Al2O3-supported catalysts, Ag/γ-Al2O3, Pt/γ-Al2O3, and Pd/γ-Al2O3. The results showed that the Ag-modified La0.6Sr0.4MnO3-based catalysts with the perovskite-type structure displayed the activity significantly higher than that of the supported precious metal catalysts, 0.1%Pd/γ-Al2O3 and 0.1%Pt/γ-Al2O3 in the temperature range of 370–573K. Over a 6%Ag/20%La0.6Sr0.4MnO3/γ-Al2O3 catalyst, the T95 temperature for methanol oxidation can be as low as 413K. Even at such low reaction temperature, there were little HCHO and CO detected in the reaction exit-gas. However, for the 0.1%Pd/γ-Al2O3 and 0.1%Pt/γ-Al2O3 catalysts, the HCHO content in the reaction exit-gas reached ∼200 and ∼630ppm at their T95 temperatures. Over a 6%Ag/La0.6Sr0.4MnO3 catalyst, the T95 temperature for ethanol oxidation can be as low as 453K, with a corresponding content of CH3CHO in the exit-gas at 782ppm; when ethanol oxidation is performed at 493K, the content of acetaldehyde in the exit-gas can be below 1ppm. Characterization of the catalysts by X-ray diffraction (XRD), TEM, XPS, laser Raman spectra (LRS), hydrogen temperature-programmed reduction (H2-TPR) and oxygen temperature-programmed desorption (O2-TPD) methods revealed that both the surface and the bulk phase of the perovskite La0.6Sr0.4MnO3 played important roles in the catalytic oxidation of the alcohols, and that γ-Al2O3 as the bottom carrier could be beneficial in creating a large surface area of catalyst. Moreover, a small amount of Ag+ doped onto the surface of La0.6Sr0.4MnO3 was able to partially occupy the positions of La3+ and Sr2+ due to their similar ionic radii, and thus, became stabilized by the perovskite lattice, which would be in favor of preventing the aggregation of the Ag species on the surface and enhancing the stability of the catalyst. On the other hand, modification of the Ag+ to the surface of La0.6Sr0.4MnO3 resulted in an increase in relative content of the surface O22−/O− species highly reactive toward the alcohols and aldehydes as well as CO. Besides, solution of low-valence metal oxides SrO and Ag2O with proper amounts in the lattice of the trivalent metal perovskite-type oxide LaMnO3 would also lead to an increase in the content of the reducible Mnn+ and the formation of anionic vacancies, which would be favorable for the adsorption-activation of oxygen on the functioning catalyst and the transport of the lattice and surface oxygen species. All these factors would contribute to the pronounced improvement of the catalyst performance.

Phase relations in the system Sr–Ir–O and thermodynamic measurements on SrIrO3, Sr2IrO4 and Sr4IrO6 using solid-state cells with buffer electrodes

The standard Gibbs energies of formation of SrIrO3, Sr2IrO4 and Sr4IrO6 have been determined in the temperature range from 975 to 1400 K using solid-state cells with (Y2O3) ZrO2 as the electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Sr–Ir–O were investigated at 1350 K. The only stable oxide detected along the binary Ir–O was IrO2. Three ternary oxides, SrIrO3, Sr2IrO4 and Sr4IrO6, compositions of which fall on the join SrO–IrO2, were found to be stable. Each of the oxides coexisted with pure metal Ir. Therefore, three working electrodes were prepared consisting of mixtures of Ir+SrO+Sr4IrO6, Ir+Sr4IrO6+Sr2IrO4, and Ir+Sr2IrO4+SrIrO3. These mixtures unambiguously define unique oxygen chemical potentials under isothermal and isobaric conditions. Used for the measurements was a novel apparatus, in which a buffer electrode was introduced between reference and working electrodes to absorb the electrochemical flux of oxygen through the solid electrolyte. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The standard Gibbs energies of formation of the compounds, obtained from the emf of the cells, can be represented by the following equations:SrIrO3: Δf (ox)Go/J mol−1=−58 860−1.23T (±650)Sr2IrO4: Δf (ox)Go/J mol−1=−82 315−2.86T (±960)Sr4IrO6: Δf (ox)Go/J mol−1=−84 690−6.78T (±1520)where Δf (ox)Go represents the standard Gibbs energy of formation of the ternary compound from its component binary oxides SrO and IrO2. Based on the thermodynamic information, chemical potential diagrams for the system Sr–Ir–O were developed.

Elastic constants, phase transition, and electronic structure of strontium oxide SrO: An ab initio Hartree-Fock study.

The static structural properties and B1-B2 phase transition of SrO were calculated at an ab initio level within the Hartree-Fock (HF) approximation using the effective core potential. The HF data were corrected a posteriori by integrating the HF charge density according to the correlation---only gradient-density-functional formulas proposed by Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)] and by Perdew [J. P. Perdew, Electronic Structure of Solids, edited by P. Ziesche and H. Eschring (Akademie Verlag, Berlin, in press)]. The HF binding energy, structural parameters, lattice parameter, bulk modulus, and elastic constants are in reasonable agreement with experiment. The correlation correction brings the binding energy into better agreement with the experiment. The transition pressure between B1 and B2 phases is in good agreement with the experimental value at the HF level, whereas it is corrected poorly by the addition of an a posteriori correlation correction.

X-ray photoelectron studies of oxygen states in metaloxyde ceramics for HTSC

Abstract Oxygen states have been studied in La2CuO4, La1.8Sr0.2CuO4-δ′ YBa2Cu3O7-δ′ EuBa2Cu3O7-δ′ T12Ba2CaCu2O8+Δ′, T12Ba2Ca2Cu3O10+Δ′ Bi2CaCu2O8+Δ′ Bi4Sr3 Ca3 Cu4O16+Δ,. by means of X-ray photoelectron spectroscopy and compared with those in oxides of the metals. It was found that the oxygen ions in the ceramics exist in several chemically nonequivalent states in which Ols electron binding energies differ within 1 eV. Binding energies Eb(Ols) for oxygen ions within Sr-O or Ba-O layers are higher a little than those in the oxides SrO or BaO respectively; Eb (Ols) for oxygen ions within La-O or T1-O or Bi-O layers are of approximately the same as those in the oxides La2O3 or T12O3 or Bij2O3 respectively; Eb(Ols) for oxygen nearby copper ions are lower than that in the oxide CuO. It was assumed that weighted average O2p level position for oxygens nearby copper was shifted to the lower binding energy side in the ceramics relative to the oxide CuO.