Ta Ions Research Articles

Role of B Ion (B = Nb, Ta) on perovskite development, lattice parameters and dielectric properties of (Ba, Pb)(Zn1/3B 2/3)O3 ceramics

Ceramic powders of Pb(Zn1/3B″2/3)O3 (where B″ is Nb or Ta ions) complex-perovskite compositions, with gradual replacements of Pb by Ba, were prepared by using a B-site precursor method. Phases developed in both systems were identified by X-ray diffraction and perovskite contents were evaluated as a function of the amount of Ba substitution. Variations of lattice parameters of the pyrochlore and perovskite structures with composition modifications are interpreted in terms of the 6- and 12-fold cation sizes. Weak-field dielectric properties of the two systems in the low-frequency range are compared.

A novel wet-chemical process to synthesise Ba(Mg 1/3Ta 2/3)O 3 nanopowders

The present work proposes an easily operated and low cost wet-chemical process for the synthesis of Ba(Mg 1/3Ta 2/3)O 3 (BMT) nanopowders. Tantalum pentaoxide, Ta 2O 5, was selected as the starting material, instead of the currently used TaCl 5. The process involves the melting of the precursor Ta 2O 5 in the presence of sodium hydroxide followed by dissolution of the cooled glassy phase and washing several times with distilled water to remove the Na + ions. A key step is the obtaining of a high quality Ta 2O 5·nH 2O colloid by controlling the concentration of Ta ion during dissolution and washing processes. The fine BMT powders were then fabricated by mixing the colloidal Ta 2O 5·nH 2O with barium acetate and magnesium acetate, according to the required molar proportions, followed by gelation and heat treatment. Nano BMT powders with an average particle size of 70 nm could be prepared at temperatures as low as 800 °C. In addition, the as prepared nanopowders revealed good sintering ability at low temperatures and the sintered nanoceramics exhibited excellent microwave dielectric properties.

Microchemical and microstructural changes of Co cemented WC induced by ion implantation

Changes in the microchemistry and microstructure of cobalt cemented tungsten carbide (WC–Co) hard alloy which were implanted with energetic Ta ions, with and without an additional C ion beam, have been investigated. Ion implantation was carried out at room temperature using a metal vapor vacuum arc source ion implanter. The extraction voltage and average current density of the ion beam was 45 kV and 50 μA/cm 2, respectively. The concentration depth profiles and microstructure of implanted the WC–Co alloy were analyzed by Rutherford backscattering spectroscopy, Auger electron spectroscopy, and glancing angle X-ray diffraction, respectively. The results showed that as compared with the control, there were no significant microstructural changes in the tungsten carbide phase of implanted WC–Co alloy substrate; both Ta implantation and Ta+C dual implantation induced a transformation from a metastable cubic form to a stable hcp form of cobalt binder phase.

Dielectronic recombination of Co-like Ag and Ta ions

Ab initio calculations of the rate coefficients for dielectronic recombination (DR) of Co-like Ag and Ta ions are performed based on Cowan's quasi-relativistic multi-configuration Hartree-Fock code. Co-like (3s23p63d10)-1 configurations and Ni-like (3s23p63d10)-24l4l' autoionization configurations are included in the present calculation. Because of the extensive distribution of autoionization state energy levels, the DR rate coefficients cannot be reproduced or interpolated by a simple analytical formula, such as the Burgess-Merts formula, or the Hagelstein approximation. We propose to use multi-set Hagelstein parameters, which is convenient in practice and can reproduce well the ab initio calculated DR rate coefficients.

Formation of Al 3Ta by Ta ion implantation into aluminum using a metal vapor vacuum arc ion source

The intermetallic compound Al 3Ta was directly formed by Ta ion implantation into aluminum with a current density of 64 μA/cm 2 using a metal vapor vacuum arc ion source at a dose of 3 × 10 17 ions/cm 2. With increasing Ta ion dose, the content of the Al 3Ta phase increased. At a dose of 7 × 10 17 ions/cm 2, the Ta-aluminide layer was about 350 nm thick. The aluminide layer played a significant role in enhancing the surface hardness of the Al matrix.

Some features of the ion-beam mixing during simultaneous ion implantation and metal deposition

Experimental results on the ion implantation of Ta and Cu ions into an Al substrate, accompanied by the deposition of these ions in the form of a surface coating are reported. The coatings composed of the implant elements exhibit a complicated structure and lead to an increase in the microhardness, adhesion properties, and corrosion resistance of the substrate. An analysis of data on the energy distribution of secondary ions shows that the surface layer of ion-implanted substrates contains intermetallic phases.

X-ray diffuse scattering associated with ferroelectric microregions inKTa1-xNbxO3

X-ray diffuse scattering for single crystals of KTa1-xNbxO3 (x = 0, 0.007 and 0.011) has been measured. For the sample of x = 0.011,peculiar x-ray diffuse scattering is observed above the phonon-frozen-intemperature (30 K). By an analysis of the diffuse scattering intensities, theaverage radius of the ferroelectric microregions is found to grow up to around4 nm with decreasing temperature from 100 K down to 30 K. Anisotropicdistributions of the diffuse scattering indicate off-centred shift of Nb andTa ions to the ⟨111⟩-direction. Moreover, lattice constants forx = 0.011 below 30 K exhibit negative expansion, which is found neither inpure KTaO3 nor in KTa1-xNbxO3 (x = 0.007) atlow temperatures. These results are successfully explained by introducing theeffective classical potential (ECP) method for the anharmonic oscillators. Thequantum contribution to mean square displacement of Nb and Ta ions from anaverage position is also calculated by the ECP method.

First-principles study ofCa2+andMn2+substituents inKTaO3

The structural properties, energetics, and dynamics of Ca{sup 2+} and Mn{sup 2+} substituents in KTaO{sub 3} are investigated from first principles. It is found that Ca substitutes for both K and Ta ions. Oxygen vacancies bind to isolated Ca ions residing at Ta sites, causing off-center Ca displacement and forming large dipoles. There is also evidence that oppositely charged defects may cluster together. Our calculations predict that the activation energy for dipole reorientation via oxygen vacancy hopping within the first-neighbor shell of Ta-substituting Ca or Mn exceeds 2 eV. On the other hand, Mn{sup 2+} substituting at the K site displaces off center along the (100) direction, also forming a dipole. This dipole can reorient via Mn hopping motion with an activation energy of {approx}0.18 eV, in reasonable agreement with experiments. We argue that, in general, metal ion hopping at the A site, not oxygen vacancy hopping, is responsible for the small activation energies found in experiments.

Secondary-electron yield from Au induced by highly charged Ta ions

The total electron yields, γ, for the emission of electrons induced by the impact of Ta q + (11⩽ q⩽41) ions with kinetic energy per charge from 15 to 150 keV/q on clean polycrystalline Au are presented. The experimental data are analyzed with use of the relations γ(θ)=γ(0) cos −fθ and γ(θ)=γ above +γ below cos −1θ . Fits of experimental data give a range of f from ∼0.6 to ∼0.17 and ratio γ above/ γ below>1. The analysis also shows that the above-surface electron yield, γ above, strongly depends on the charge state ( γ above≈ q) and the below one, γ below, is proportional to the ion impact velocity ( γ below≈ v). The correction of cos −1θ -dependence for fit improvement is discussed.

Microstructure of a Complex Oxide, Ho2MnxTa2−xO7(x≅ 1.0), with a Pyrochlore‐Related Structure

The ternary compound Ho2MnxTa2−xO7 was synthesized in air at 1523 K. Structural characterization of the compound was taken by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The compound possessed a trigonal super cell derived from a rhombohedral basic cell with the a/2 of the trigonal super cell. The super cell was caused by the ordering of Mn and Ta ions and the derived structure model was in agreement with that of the zirkelite structure with the space group P3121. The compound had stacking disorder with different stacking sequences along the c‐axis. An orientation anomaly in the super cell reflections revealed that the super cell had an incommensurate nature.

Novel Ta-bronzes. The crystal structure and conductivity of K6Ta6.5O15+xF6+ywith partialy reduced Ta ions

Novel Ta-bronzes. The crystal structure and conductivity of K₆Ta_6.5O_15+xF_6+ywith partialy reduced Ta ions

Electronic structure and total energy of SrBi/sub 2/Ta/sub 2/O/sub 9/ by first-principles calculations

The results of first-principles calculations of the electronic structure and the total energy in strontium bismuth tantalate, SrBi(2)Ta(2)O(9) (SBT), with respect to Ta ion displacements, are reported. In pseudotetragonal SBT and its solid solutions, bismuth oxide, [(Bi(2)O(2))(2+)], layers alternate with double strontium tantalate, [(Sr(2)Ta(2)O(7))(2-)], perovskite layers. The dual crystal chemistries give rise to dual electronic and dielectric properties that are anisotropic. The calculated electronic structure of SBT indicates that the absence of an energy gap in the vicinity of the Fermi level stems from lowering of the Sr orbital energies due to its lower electronegativity relative to Ta and Bi ions, and significant hybridization between Sr, Ta, Bi and O ions. Although charge carriers in the "semimetallic" (Sr(2)Ta(2)O(7))(2-) sublattice have a large effective mass, the (Bi(2)O(2))(2+) sublattice is insulating. The calculated partial and total densities of states provide alternative but plausible explanations to the reported spectroscopic data. The total energy anisotropy indicates that multiple phase transformations, and anisotropies in the polarization retention and coercive field (E(c)), are expected. Explanations of the fatigue-free behavior and leakage current (J(L)) and its anisotropy of SBT, and comments on optical transparency and calculating methods for band structure of SBT are forwarded.

Influence of electromagnetic anisotropy on the flux-pinning strength of columnar defects inBi2.2−xPbxSr1.8CaCu2.0Oy

Magnetization measurements have been performed on Bi(Pb)2212 single crystals with various electromagnetic anisotropies $({\ensuremath{\gamma}}^{2}=1.2\ifmmode\times\else\texttimes\fi{}{10}^{3}\ensuremath{\sim}4.4\ifmmode\times\else\texttimes\fi{}{10}^{4})$ before and after introducing columnar defects by Ta ion irradiation. The irreversibility fields of these crystals increased systematically with decreasing ${\ensuremath{\gamma}}^{2}$ at various reduced temperatures ${t=T/T}_{\mathrm{c}},$ indicating that the smaller anisotropy makes the columnar defects substantially more effective in flux pinning. The record-high irreversibility field and critical current density for single crystals of the Bi2212 phase was observed in our oxygen-overdoped Bi(Pb)2212 with columnar defects. This study experimentally reveals the reduction of the electromagnetic anisotropy and the introduction of pinning centers work cooperatively in high-${T}_{c}$ superconductor compounds.

Metal ion mixing in diamond

We have carried out some investigations of the mixing of thin metal films into diamond by energetic metal ion bombardment. Free-standing diamond films were made by microwave plasma-assisted CVD, onto which films of Nb or Ta, approximately 100-Å thick, were deposited using a filtered vacuum arc plasma technique. The metalized diamond was then bombarded with a Ta and Nb ion-beam, respectively, at an energy of 150 keV and to an applied dose of ∼7×10 16 ions/cm 2. The Nb and Ta depth profiles were measured by 2 MeV He + Rutherford backscattering spectrometry. Intense intermixing was produced between the original metal overlay, the diamond matrix, and the implanted atoms; and the concentration depth profiles were found to be well-described by the predictions of the TRIM code. Here, we outline the techniques used for diamond synthesis and the preparation of free-standing films, the vacuum arc plasma deposition of Nb and Ta thin films, and the Ta and Nb ion implantations; and we describe our observations of the ion-mixed films formed in this way.

Laser induced direct implantation of ions

Results on iodine laser production of Ag, Au, Pb, Sn and Ta ions are presented and experiments on their implantation into steel, Al and plastics are compared and discussed. Ions were implanted without additional acceleration into metals to the depth of several hundreds of nanometers, and into plastics to a depths of up to several micrometers.

A series of bismuth layer-structured ferroelectrics

The general formula, Sr m−3+x Bi4−x Ti m−x Ta x O3m+3 (m=2 and 3) is a phase relation between well-known bismuth layer-structured ferroelectrics (BLSF) such as Bi4Ti3O12 and SrBi2Ta2O9 including a perovskite compound SrTiO3. The series was discussed to form the layer structure with the numbers m=2 and 3 of layer, where x is the number of Ta ions in the layer structure and 1≦x≦2 for m=2 and 0≦x≦2 for m−3. The Curie temperature, T c' increase as the Sr concentration decreases. From the measurements of D-E hysteresis loops by using a standard Sawyer-Tower circuit, the value of 2P r on Sr0.3Bi3.7Ta2.7Ta0.3O12 (m=3) ceramics was the largest (2P r=24.6 μC/cm2) in above BLSF series.

Electrical properties of Li2O-La2O3-SiO2 electrode glasses after Ta2O5 doping and Ta implantation

Electrical conductivities, σ, of the Li2O-La2O3-SiO2 glasses were investigated as functions of Ta2O5 doping and Ta ion-implantation. A linear relationship between logarithm σ and the inverse of the sample temperature, T, was found in 2 to 4 mol% Ta2O5 doped Li2O-La2O3-SiO2 glasses. The conductivity increases as Ta2O5 content increases at sample temperatures above 100°C. Fluences of 50 keV Ta ions per cm2 from 5 × 1016 to 2 × 1017 were implanted into 0% and 2% Ta2O5 containing Li2O-La2O3-SiO2 glass samples. The activation energy of the conductivity was deduced from the relation between log σ and 1/T. It was found in implanted samples that the conductivity increased, but the activation energy and Tk−100 decreased, where Tk−100 is the sample temperature when the conductivity reaches 100 × 10−1 S/cm. However, the Ta2O5 containing implanted samples show higher conductivities, lower activation energies and lower Tk−100. X-ray photoelectron spectroscopy (XPS) was used to study the structural modification introduced by implantation. Bridging oxygen (BO) and non-bridging oxygen (NBO), were observed in all samples. The changes in relative concentrations of BO and NBO before and after implantation clearly indicate the structure modification which results in the increase of the conductivity. It was clearly demonstrated in this study that both doping Ta2O5 and implanting Ta ions enhance the conductivity of Li2O-La2O3-SiO2 electrode glasses.

Epitaxial Sr-Bi-Ta Oxide Films of Cubic Fluorite-Like Structure

Epitaxial Sr-Bi-Ta oxide films of a cubic fluorite-like structure were grown by pulsed laser deposition. As the laser fluence increased, the lattice constant decreased. It was revealed that the Ta ion concentration was closely related with the change in the lattice constant. From selected area electron diffraction measurements, it was observed that the films had a superstructure which seemed to come from ordering of metal ions.

Facilitated transport of niobium(V) and tantalum (V) with supported liquid membrane using TBP as carrier

The transfer of Nb(V) and Ta(V) ions in a chloride medium across a supported liquid membrane containing tributyl phosphate as carrier has been investigated. Conditions for feed solutions were analyzed by means of liquid–liquid extraction experiments. The transport experiments were carried out with a permeation cell with a continuous flow system and constant agitation. The hydrochloric acid concentration in the feed solution has a marked effect on Nb(V) transport. With increasing hydrochloric acid concentration the transport of Niobium (V) increased and a maximum flux between 6 and 9 M of HCl was obtained. The Ta(V) was transported in small amounts at HCl concentration up 6 M, so that a selective separation of Nb(V) from Ta(V) could thus be performed.

Micro channel plate gains for Ta 10+–Ta 44+ ions, measured in the energy range from 3.7 keV/q up to 150.7 keV/q

The procedure of calibration of a detector assembly consisting of a micro channel plate detector operated in a Chevron configuration is described. The analog particle gains of Ta ions with charge states ranging from q=10 + to 44 + and ion impact energies from 3.2 to 153.2 keV/ q have been measured. For the investigated range of ion impact energies we have stated that for tantalum charge states of 10 +–20 + the secondary ion–electron emission coefficient is dominated by the kinetic emission of electrons. Potential effects being visible for the charge states above 20 +.