Mössbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia

The local environment of implanted ¹¹¹Ag (t _1/2 = 7.45 d) in single-crystalline [0001] ZnO was evaluated by means of the perturbed angular correlation (PAC) technique. Following the 60 keV low dose (1 × 10¹³ cm⁻²) ¹¹¹Ag implantation, the PAC measurements were performed for the as-implanted state and following 30 min air annealing steps, at temperatures ranging from 200 to 1050°C. The results revealed that 42% of the probes are located at defect-free S_Zn sites (ν _Q ∼ 32 MHz, η = 0) in the as-implanted state and that this fraction did not significantly change with annealing. Moreover, a progressive lattice recovery in the near vicinity of the probes was observed. Different EFGs assigned to point defects were furthermore measured and a general modification of their parameters occurred after 600°C. The 900°C annealing induced the loss of 30% of the ¹¹¹Ag atoms, 7% of which were located in regions of high defects concentration.     

Polymer electrolytes based on polycarbonates and their electrochemical and thermal properties

Polycarbonates (4a–d) with various side chain lengths were synthesized by the reaction of 1,4-bis(hydroxyethoxy)benzene derivatives and triphosgene in the presence of pyridine. The polymer electrolytes composed of 4a–d with lithium bis(trifluoromethanesulfonyl)imide (LiN(SO₂CF₃)₂, LiTFSI) were prepared, and their ionic conductivities and thermal and electrochemical properties were investigated. 4d-Based polymer electrolyte showed the highest ionic conductivity values of 1.0?×?10^?4?S/cm at 80 °C and 1.5?×?10^?6?S/cm at 30 °C, respectively, at the [LiTFSI]/[repeating unit] ratio of 1/2. Ionic conductivities of these polycarbonate-based polymer electrolytes showed the tendency of increase with increasing the chain length of oxyethylene moieties as side chains, suggestive of increased steric hindrance by side chains. Unique properties were observed for the 4a(n?=?0)-based polymer electrolyte without an oxyethylene moiety. All of polycarbonate-based polymer electrolytes showed good electrochemical and thermal stabilities as polymer electrolytes for battery application.     

Solid polymer electrolytes based on squaric acid structure

Poly(squarate)s (PPS-1 and PPS-2) were synthesized by the reaction of squaryl dichloride with hydroquinone for PPS-1 and with 2,5-diethoxy-1,4-bis(trimethylsilyloxy)benzene for PPS-2, and the ionic conductivities, thermal properties, and electrochemical and thermal properties of their polymer electrolytes with LiN(CF₃SO₂)₂ were investigated. The ionic conductivity increased with increasing the lithium salt concentration for the PPS-1–LiN(CF₃SO₂)₂ electrolyte, and the highest ionic conductivities of 8.60 × 10⁻⁵ S/cm at 100 °C and 9.57 × 10⁻⁸ S/cm at 30 °C were found at the [Li] to [O] ratio of 2:1. And also, the ionic conductivity for the PPS-1–LiN(CF₃SO₂)₂ electrolyte increased with an increase in the lithium salt concentration, reached a maximum value at the [Li] to [O] ratio of 1:2, and then decreased. The highest ionic conductivity was to be 1.04 × 10⁻⁵ S/cm at 100 °C and 1.71 × 10⁻⁸ S/cm at 30 °C, respectively. Both polymer electrolytes exhibited relatively better electrochemical and thermal stabilities. Addition of the PPS-1 as a plasticizer into the poly(ethylene oxide) (PEO)–LiN(CF₃SO₂)₂ electrolyte system suppressed the crystallization of PEO, and improved the ionic conductivity at room temperature. Invited paper dedicated to Professor W. Weppner on his 65th birthday.     

Reactive sputtering deposition and electrochemical characterisation of thin solid electrolyte membranes for solid oxide fuel cells

Solid oxide fuel cells directly convert the chemical energy of a fuel into electricity. To enhance the efficiency of the fuel cells, the thickness of the gastight solid electrolyte membranes should be as thin as possible. Y₂O₃-stabilised ZrO₂ (YSZ) electrolyte films were prepared by reactive sputtering deposition using Zr/Y targets in Ar/O₂ atmospheres. The films were 5 – 8 μm thin and were deposited onto anode substrates made of a NiO/YSZ composite. After deposition of a cathode with the composition La_0.65Sr_0.35MnO₃ the electrochemical properties of such a fuel cell were tested under operating conditions at temperatures between 600 °C and 850 °C. Current-voltage curves were recorded and impedance measurements were performed to calculate apparent activation energies from the fitted resistance data. The conductivity of the YSZ films varied between 4.6·10⁻⁶ S/cm and 2.2·10⁻⁵ S/cm at 400 °C and the fuel cell gave a reasonable power density of 0.4 W/cm² at 0.7 V and 790 °C using H₂ with 3 % H₂O as fuel gas. The gas compositions were varied to distinguish the electrochemical processes of the anode and cathode in the impedance spectra. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

Ac-conductivity and dielectric relaxations above glass transition temperature for parylene-C thin films

45% semi-crystalline parylene-C (–H₂C–C₆H₃Cl–CH₂–) _n thin films (5.8 μm) polymers have been investigated by broadband dielectric spectroscopy for temperatures above the glass transition (T _g =90°C). Good insulating properties of parylene-C were obtained until operating temperatures as high as 200°C. Thus, low-frequency conductivities from 10⁻¹⁵ to 10⁻¹² S/cm were obtained for temperatures varying from 90 to 185°C, respectively. This conductivity is at the origin of a significant increase in the dielectric constant at low frequency and at high temperature. As a consequence, Maxwell–Wagner–Sillars (MWS) polarization at the amorphous/crystalline interfaces is put in evidence with activation energy of 1.5 eV. Coupled TGA (Thermogravimetric analysis) and DTA (differential thermal analysis) revealed that the material is stable up to 400°C. This is particularly interesting to integrate this material for new applications as organic field effect transistors (OFETs). Electric conductivity measured at temperatures up to 200°C obeys to the well-known Jonscher law. The plateau observed in the low frequency part of this conductivity is temperature-dependent and follows Arrhenius behavior with activation energy of 0.97 eV (deep traps).     

Effect of the annealing temperature of thin Hf0.3Zr0.7O2 films on their energy storage behavior

With increasing annealing temperature (T_anneal), the magnitude of the electric fields for the antiferroelectric‐to‐ferro‐electric (E_AF) and ferroelectric‐to‐antiferroelectric (E_FA) transition of a 9.2 nm thick Hf_0.3Zr_0.7O₂ film decreased. The energy storage densities of the Hf_0.3Zr_0.7O₂ films crystallized at 400 °C, 500 °C, and 600 °C were as large as 42.2 J/cm³, 40.4 J/cm³, and 28.3 J/cm³, respectively, at the electric field of 4.35 MV/cm. The maximum dielectric constant of the Hf_0.3Zr_0.7O₂ film crystallized at 600 °C was the largest (～46) as it had the smallest E_AF and E_FA, whereas the leakage current density of the film crystallized at 400 °C was the smallest. The 400 °C of T_anneal was the optimum condition for energy storage application. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Defect reduction and surface passivation of SiO2/Si by heat treatment with high-pressure H2O vapor

Heat treatment with high-pressure H₂O vapor was applied to improve interface properties of SiO₂/Si and passivate the silicon surface. Heat treatment at 180–420 °C with high-pressure H₂O vapor changed SiO_x films, 150 nm thick formed at room temperature by thermal evaporation in vacuum, into SiO₂ films with a Si-O-Si bonding network similar to that of thermally grown SiO₂ films. Heat treatment at 130 °C with 2.8×10⁵ Pa H₂O for 3 h reduced the recombination velocity for the electron minority carriers from 405 cm/s (as-fabricated 150-nm-thick SiO_x/Si) to 5 cm/s. Field-effect passivation was demonstrated by an additional deposition of defective SiO_x films on the SiO₂ films formed by heat treatment at 340 °C with high-pressure H₂O vapor. The SiO_x deposition reduced the recombination velocity from 100 cm/s to 48 cm/s. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Pyroelectric properties of BiFeO3 ceramics prepared by a modified solid-state-reaction method

BiFeO₃ (BFO) ceramics were prepared by a modified solid-state-reaction method which adopts a higher heating/cooling rate during the sintering process than usually used. It was found that the calcination temperature T _cal (from 400 to 750°C) does not influence the BFO phase formation, while the sintering temperature T _sin (from 815 to 845°C) dominates the phase purity. The optimum sintering temperature was in the range from 825 to 835°C. The optimized samples exhibit saturated ferroelectric hysteresis loops with a remnant polarization of 13.2 μC/cm². The measured piezoelectric coefficient d ₃₃ was 45 pC/N. No remnant magnetization was observed in all of the samples. The pyroelectric properties were studied as a function of temperature and frequency. A pyroelectric coefficient as high as 90 μC/m² K was obtained at room temperature in the optimized sample. An abrupt decrease of the pyroelectric coefficient was observed at temperatures between 70 and 80°C. On the basis of our results, BFO may have the potential for pyroelectric applications.     

Ag(100)表面氧吸附的密度泛函理论和STM图像研究

用密度泛函理论研究了氧原子的吸附对于Ag(100)表面结构和电子态的影响.通过PAW总能计算研究了p(1×1)、c(2×2)和(2^1/2×22^1/2)R45°等几种原子氧覆盖度下的吸附结构,以及在上述结构下Ag(100)表面的弛豫特性、吸附能量、功函数等一系列物理量.研究表明：在(2^1/2×22^1/2)R45°-2O吸附Ag(100)表面的情况下,每格两列就会缺失 关键词： Ag(100)表面氧吸附 缺列再构 STM图像     

Ag(100)表面氧吸附的密度泛函理论和STM图像研究

用密度泛函理论研究了氧原子的吸附对于Ag(100)表面结构和电子态的影响.通过PAW总能计算研究了p(1×1)、c(2×2)和(2^1/2×22^1/2)R45°等几种原子氧覆盖度下的吸附结构，以及在上述结构下Ag(100)表面的弛豫特性、吸附能量、功函数等一系列物理量.研究表明：在(2^1/2×22^1/2)R45°-2O吸附Ag(100)表面的情况下，每格两列就会缺失     

The study of damage and optical properties in LiNbO3 implanted by MeV Er and He ions

Abstract

Two LiNbO₃ (X and Y cut) crystals from different companies were implanted by 3.0 MeV Er ions to a dose of 7.5 × 10¹⁴ ions/cm² and 3.5 × 10¹⁴ ions/cm² with different beam current densities, respectively. After annealing at 1060°C in air for 2 hours, one LiNbO₃ sample was implanted by 1.5 MeV He ions to a dose of 1.5 × 10¹⁶ ions/cm². The Rutherford backscattering/channeling and prism coupling method have been used to study the damage and optical properties in implanted LiNbO₃. The results show: (1) the damage in LiNbO₃ created by 3.0 MeV Er ions depends strongly on the beam current density; (2) after annealing at 1060°C in air for 2 hours, a good Er doped LiNbO₃ crystal was obtained; (3) there is waveguide formation possible in this Er-doped annealed LiNbO₃ after 1.5 MeV He ion implantation. It is suggested that annealing is needed to remove the damage created by MeV Er ions before the MeV He ion implantation takes place, to realize the waveguide laser for Er doped LiNbO₃.     

多重散射团簇方法对吸附系统SO2/Ag(110)的理论分析

利用多重散射团簇方法(MSC)对吸附系统SO₂/Ag(110)的S原子K边X射线吸收精细结构谱(NEXAFS)作了理论分析.研究表明,覆盖度为0.5时,吸附的SO₂的S—O键长比气体状态时增长了(0.014±0.006)nm,OSO键角减小了15°±5°;SO₂分子的S原子处于芯位,但两个O原子处于不对称的位置;分子平面与(110)的夹角约为52°,同时分子平面相对衬底表面法线有一小角度的倾斜.MSC计算证实了该吸附系统存在一介于π^{关键词： X射线吸收精细结构 2/Ag(110)')" href="#">吸附系统SO₂/Ag(110) 多重散射团簇方法}     

Investigation on FR(LT)–FR(HT) phase transition and pyroelectric properties of pulsed laser deposited Pb(Zr0.93Ti0.07)O3 thin films

The preparation process, crystallinity and electrical properties of pulse laser deposited Pb(Zr_xTi_1−x)O₃ (PZT) thin films were investigated in this paper. PZT (x = 0.93) thin film samples deposited at different substrate temperatures were prepared. Si (1 1 0) was the substrate; Ag and YBCO were the top electrode and the bottom electrode respectively. The bottom electrode YBCO was deposited on the Si substrate by pulsed laser deposition (PLD), and then PZT was epitaxially deposited on YBCO also by PLD. After annealing, the top electrode Ag was prepared on PZT by thermal evaporation, and then the Ag/PZT/YBCO/Si structured thin films were obtained. The XRD and the analysis of their electrical characters showed that, when the substrate temperature was elevated from 600 °C to 800 °C, the crystallinity and electrical properties of PZT thin films became better and better, and the F_R(LT)–F_R(HT) phase transition of PZT (x = 0.93) thin films occurred at 62 °C. The PZT film deposited at 800 °C had the best pyroelectric properties, and when the F_R(LT)–F_R(HT) phase transition of this film occurred, the peak value of pyroelectric coefficient (p) was obtained, with a value of 1.96 × 10⁻⁶ C/(cm² K). The PZT film deposited at 800 °C had the highest remnant polarization (P_r) and the lowest coercive field (E_c), with the values of 34.3 μC/cm² and 41.7 kV/cm respectively.     

A novel anode-supported stable BaCe0.7Ta0.1Y0.2O3− δ membrane prepared by all-solid-state process for solid oxide fuel cells

BaCe_0.7Ta_0.1Y_0.2O_{3− δ} (BCTY) and BaCe_0.8Y_0.2O_{3− δ} (BCY) were synthesized by solid-state reaction method at 1,300 °C for 20 h. After being exposed in 3% CO₂ + 3% H₂O + 94% N₂ at 700 °C for 20 h, the BCTY exhibited adequate chemical stability against carbonations while BCY decomposed into BaCO₃ and CeO₂. The BCTY showed the similar thermal expansion behavior to BCY from room temperature to 1,000 °C in air. The BCTY displayed a conductivity of 0.007 S/cm at 700 °C in humid hydrogen, lower than that of BCY (0.009 S/cm). A fuel cell with 10-μm thick BCTY membrane prepared through an all-solid-state process exhibited 1.004 V for OCV, 330 mW/cm² for maximum output at 700 °C, respectively. Short-term test shows that the fuel cell performance does not degrade after 20 h.     

Size-dependent luminescence in Y2Si2O7 nanoparticles doped with Ce3+ ions

Powders and thin films of nanocrystalline yttrium disilicate (Y₂Si₂O₇) doped with Ce³⁺ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic properties compared. The triclinic α-Y₂Si₂O₇ form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type monoclinic β-Y₂Si₂O₇ polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at 1300°C the basically pure triclinic α-Y₂Si₂O₇ phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure and luminescence properties of the fabricated materials are presented and discussed.     

Phase stability,thermal, electrical and structural properties of (Bi2O3)1−x−y(Sm2O3)x(CeO2)y electrolytes for solid oxide fuel cells

In this study, (Bi₂O₃)_1?x?y(Sm₂O₃)_x(CeO₂)_y ternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x = 10–15, y = 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi₂O₃ phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO₂ molar ratio at a fixed molar ratio of Sm₂O₃. The highest electrical conductivity obtained for the (Bi₂O₃)_0.65(Sm₂O₃)_0.15(CeO₂)_0.20 system was 1.55 × 10^?2 (Ω.cm)^?1 at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV.     

An application of oxide and silver electrode on the BaO-doped Bi2O3 electrolyte

Oxide and silver paste were applied on the BaO-doped Bi₂O₃ electrolyte and their behavior was studied as a function of temperature and oxygen partial pressure. Interface resistance of most oxide/electrolyte were of the same order of magnitude with those of Ag paste/electrolyte in air (300–500°C). A high electrode capacitance of (0.8–1.7)×10^?2 F/cm² was observed for the silver electrode at 450°C in the P_O2 region of 1–10^?5 atm.     

Ion-electron transfer in solid solutions Rb2 ? 2xFe2 ? xPxO4

The rubidium monoferrite RbFeO₂-based solid solutions with the composition Rb_{2 − 2x} Fe_{2 − x} P _x O₄ have been synthesized, and their crystal structure and the temperature and concentration dependences of the total and electron conductivities have been studied. The introduction of P⁵⁺ ions has been found to sharply decrease the electron conductivity that prevails in pure rubidium monoferrite and, at the same time, to increase the ionic conductivity. The latter becomes dominant as the phosphorus concentration increases. The maximum rubidium-cation conductivity of the materials under study is ∼3 × 10⁻² S/cm at 300°C and ∼3 × 10⁻¹ S/cm at 700°C. The results have been compared with the previously obtained data for similar solid solutions based on rubidium monogallate and monoaluminate.     

Disorder‐induced symmetry lowering in Ba(Y1/2Nb1/2)O3 ceramics probed by Raman spectroscopy

This work investigates the evolution of the crystal structure of microwave‐hydrothermal synthesized Ba(Y_1/2Nb_1/2)O₃ powders as a function of firing temperature by Raman spectroscopy. The samples were produced at 200 °C and fired at temperatures ranging from 600 to 1600 °C. Raman spectra were obtained at room temperature for all samples and the results showed that materials fired at 1600 °C exhibited tetragonal (I4/m or ) structure, whereas those fired at lower temperatures exhibited the triclinic (P1 or C_i¹) structure. The results were compared with those observed for ceramics obtained by conventional solid‐state methods. It is believed that the lowering of the symmetry verified in materials fired below 1600 °C is a consequence of the local disorder of Y⁺³ and Nb⁺⁵ ions in octahedral sites. Copyright © 2008 John Wiley & Sons, Ltd.     

Long-range chemical interactions in solid-state reactions: effect of an inert Ag interlayer on the formation of L10-FePd in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) trilayers

The effect of 0, 0.5, and 1?μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1)/MgO(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1)/MgO(0?0?1) trilayers has been studied using X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400?°C. As the annealing temperature is increased above 400?°C, a solid-state synthesis of an ordered L1₀-FePd phase begins in the Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500?°C leads to the formation of a disordered Fe_xPd_1?x(0?0?1) phase; however, in samples lacking the Ag layer, the synthesis of Fe_xPd_1?x is preceded by the formation of an ordered L1₂-FePd₃ phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2?μm-thick Ag film does not prevent the synthesis of the L1₀-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 10⁴ times greater than an ordinary chemical bond length.