Comparative study of LNO, LSCO and LSMO as electrode layers for microelectronic capacitors by dynamic SIMS

Chemical solution-deposited multilayer systems of SrTiO₃ (STO)/X/Pt/TiO₂/SiO₂/Si [where X=LaNiO₃ (LNO), La_0.5Sr_0.5CoO₃ (LSCO), La_0.7Sr_0.3MnO₃ (LSMO)] were investigated by dynamic secondary-ion mass spectrometry (SIMS). The STO layer is intended to serve as a dielectric layer for a capacitor, the conducting layers ‘X’ are a buffer layer intended to eliminate fatigue effects, which usually occur at the Pt/STO interface. Depth profiles of the main components were obtained, revealing intense diffusion processes, which must have occurred during the deposition/crystallisation processes. Furthermore, Al impurities from the substrate, most probably originating from the Pt-sputter process, are preferentially found at the interfaces. Ti is found to diffuse from the (isolating) STO layer into the conductive ‘X’ oxide layers, where a region of constant concentration is observable in all three sample systems.     

AFM study of LaNiO3 thin films on various single crystal substrates prepared by using a metal naphthenate precursor

We investigated surface morphology of LaNiO₃ thin films on LaAlO₃ (100), SrTiO₃(100), MgO(100) and sapphire (0001) substrates by using atomic force microscope (AFM). Chemical solution deposition process was adopted to prepare thin film with a metal naphthenate precursor. The power spectral density of thin films on LaAlO₃ and SrTiO₃ substrates exhibits an inflated shape at a spatial frequency into 10 μm⁻¹ range with uniformly formed small grains, while LaNiO₃ on sapphire showed a high root mean square roughness.     

The electrochemical hydrogen storage of CNTs synthesized by CVD using LaNi5 alloy particles as catalyst and treated with different temperature in nitrogen

The multi-wall carbon nanotubes (MWNTs) were synthesized by chemical vapor deposition (CVD) using LaNi₅ alloy particles as catalyst. The effect of 40–60 nm MWNTs treated with different temperature in nitrogen on the electrochemical properties of CNTs–Ni electrode were investigated. Three-electrode system was introduced for testing electrochemical hydrogen storage of the electrode. The CNTs–Ni electrodes were used as the working electrode, which were prepared by mixing MWNTs and Ni powder in a weight ratio of 1:10 (MWNTs:Ni). Ni(OH)₂/NiOOH worked as the counter electrode and Hg/HgO as the reference electrode. A 6 mol/L KOH solution acted as the electrolyte. MWNTs treated with different temperature in nitrogen ambient represented a great discrepancy in the electrochemical hydrogen storage capability under the same testing condition. The CNTs–Ni electrodes with 40–60 nm diameter CNTs which were treated in a temperature of 800 °C in nitrogen has the best electrochemical hydrogen storage capacity of 588.1 mAh/g and a corresponding discharging plateau voltage of 1.18 V. From 500 to 800 °C, the higher temperature the MWNTs treated, the better the electrochemical hydrogen storage property of them is. This shows that the temperature of treatment is an important factor that influences electrochemical hydrogen storage performance of MWNTs.     

Low temperature synthesis of nanocrystalline lanthanum monoaluminate powders by chemical coprecipitation

Nanocrystalline lanthanum monoaluminate (LaAlO₃) powders were prepared by chemical coprecipitation using 25 vol.% of NH₄OH, 0.05 M La(NO₃)₃·6H₂O and 0.05 M Al(NO₃)₃·9H₂O aqueous solutions as the starting materials. Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analyses (TGA/DTA), X-ray diffraction (XRD), Raman spectrometry, specific surface area (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED) were utilized to characterize the LaAlO₃ powders prepared by chemical coprecipitation. The crystallization temperature of the LaAlO₃ precursor gels precipitated at pH 9 is estimated as 810 °C by TG/DTA. The XRD pattern of the LaAlO₃ precursor gels precipitated at pH 8–12 and calcined at 700 °C for 6 h shows a broad arciform continuum exist between 24° and 32° and sharp peaks of LaAlO₃ except the precursor gels precipitated at pH 9. For the LaAlO₃ precursor gels precipitated at pH 9 and calcined at 700 °C for 6 h, the formation of the perovskite LaAlO₃ phase occurs and the presence of crystalline impurities is not found. The crystallite size of LaAlO₃ slightly increases from 37.8 to 41.5 nm with calcination temperature increasing from 700 to 900 °C for 6 h. The LaAlO₃ powders prepared by chemical coprecipitation have a considerably large specific surface of 30 m²/g. The relative density greater than 97% is obtained when these nanocrystalline LaAlO₃ powders are sintered at 1550 °C for 2 h.     

Effects of the solution temperature and the pH on the electrochemical properties of the surface oxide films formed on Alloy 600

The surface oxide films on Alloy 600 have been investigated as a function of the solution temperature and the pH by using a cyclic voltammetry, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and a depth profiling by Auger electron spectroscopy (AES). H₃BO₃, Na₂SO₄ and NaOH aqueous solutions with temperatures in the range of 30–300 °C were used as the test solutions. As the solution temperature of the 0.5 M H₃BO₃ increased, the thickness of the passive film increased but the resistance of the passive film was diminished, which is coincident with a solution temperature dependency of the passive current in the potentiodynamic curve. The inner oxide film on Alloy 600 was distinguishable from the Cr-rich outer oxide film above 100 °C. From the Mott–Schottky relation, the oxide formed in 0.5 M H₃BO₃ at 300 °C showed a p-type semiconductor property, accompanied by a Cr-rich oxide film throughout the whole oxide film unlike the n-type oxide films up to 250 °C. The oxide resistance of the passive film decreased in the order of 0.5 M H₃BO₃, 0.1 M NaOH and 0.5 M Na₂SO₄, which is consistent with the pH dependency of the passive current. Ni-rich oxide films of a p-type were formed in the 0.5 M Na₂SO₄ or 0.1 M NaOH.     

Fabrication of anatase-type TiO2 films by reactive pulsed laser deposition for photocatalyst application

TiO₂ films having anatase crystal structure were prepared on glass substrates by reactive pulsed laser deposition using a metallic Ti target in an O₂ gas ambient. At a fixed substrate temperature of 400 °C, the crystalline structure, surface morphology, optical properties and photocatalytic activity of the TiO₂ films were greatly affected by the O₂ gas pressure. It was found that nearly pure anatase-phase TiO₂ film can be obtained under an O₂ pressure of 15 Pa, which had smallest grain size among the films deposited under various O₂ gas pressure from 5 to 30 Pa. This film also showed good optical transmittance between the wavelength of 200 and 800 nm and high photocatalytic efficiency on the decomposition of methylene blue in aqueous solution. Discussions were given to explain the experimental phenomena.     

Growth kinetics and oxidation behavior of WSi2 coating formed by chemical vapor deposition of Si on W substrate

The growth kinetics of WSi₂ coating formed by chemical vapor deposition (CVD) of Si on a W substrate at temperatures between 1000 and 1200 °C using SiCl₄–H₂ gas mixtures was investigated and its isothermal oxidation resistance in 80% Ar–20% O₂ atmosphere was evaluated at temperatures between 800 and 1300 °C. WSi₂ coating grew with a parabolic rate law after an initial incubation period, indicating the diffusion-controlled growth. The activation energy for growth of WSi₂ coating was about 42.5 kcal/mol. The isothermal oxidation rate of WSi₂ coating increased with increasing oxidation temperature but rapidly decreased at 1300 °C. The oxidation product of WSi₂ coating was composed of the WO₃ particles embedded in the amorphous SiO₂ matrix at below 1200 °C but consisted of only SiO₂ phase at 1300 °C. The fast oxidation behavior of WSi₂ coating at below 1200 °C was attributed to the formation of many cracks and pores, i.e. short-circuit diffusion path of oxygen, within the oxide scale, which resulted from the internal stress generated both by the large volume expansion caused by the oxidation reactions of WSi₂ and by the evaporation of WO₃ phase. The slow oxidation behavior of WSi₂ coating at 1300 °C was due to the exclusive formation of a slow-growing continuous SiO₂ scale by the rapid evaporation of WO₃ phase.     

Sm0.5Sr0.5CoO3 cathode material from glycine-nitrate process: Formation, characterization, and application in LaGaO3-based solid oxide fuel cells

Cathode material Sm_0.5Sr_0.5CoO₃ (SSC) with perovskite structure for intermediate temperature solid oxide fuel cell was synthesized using glycine-nitrate process (GNP). The phase evolution and the properties of Sm_0.5Sr_0.5CoO₃ were investigated. The single cell performance was also tested using La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolyte and SSC as cathode. The results show that the formation of perovskite phase from synthesized precursor obtained by GNP begins at a calcining temperature of 600 °C. The single perovskite phase is formed completely after sintering at a temperature of 1000 °C. The phase formation temperature for SSC with complete single perovskite phase is from 1000 to 1100 °C. The SrSm₂O₄ phase appeared in the sample sintered at 1200 °C. It is also found that the sample sintered at 1200 °C has a higher conductivity. The electrical conductivity of sample is higher than 1000 S/cm at all temperature examined from 250 to 850 °C, and the highest conductivity reaches 2514 S/cm at 250 °C. The thermal expansion coefficient of sample SSC is 22.8 × 10⁻⁶ K⁻¹ from 30 to 1000 °C in air. The maximum output power density of LSGM electrolyte single cell attains 222 and 293 mW/cm² at 800 and 850 °C, respectively.     

Effect of addition of Cu into ZrOx film on its properties

The article reports on the effect of addition of Cu into the ZrO₂ film on its structure, physical and mechanical properties. The ZrO₂ and Zr–Cu–O films were reactively sputtered using a dc unbalanced magnetron from Zr (99.9) and ZrCu (90/10 at.%) targets in Ar + O₂ mixture at the substrate temperature T_s = 300, 400 and 550 °C and total sputtering gas pressure p_T = 1 Pa on steel, Si(100) and glass substrates. The structure of films was characterized by an X-ray diffraction (XRD) and mechanical properties, i.e. microhardness H, effective Young's modulus E* = E / (1 − ν²) and elastic recovery W_e, were measured using a microhardness tester; E and ν are the Young's modulus and the Poisson ratio, respectively. The film brittleness was characterized by the formation of cracks during the diamond indenter impression into it. 5 μm thick ZrO₂ films prepared in the oxide mode of sputtering are crystalline (m-ZrO₂) and exhibit relatively (i) high hardness H≈16 GPa and (ii) low ratio H³ / E*²≈0.11 GPa. The Zr–Cu–O films with low (≤ 2 at.%) Cu content exhibit (i) crystalline structure, (ii) higher H, (iii) lower (− 1.5 GPa) macrostress σ and (iv) higher ratio H³ / E*²≈0.14 GPa. On the contrary, the Zr–Cu–O films with high (24 to 44 at.%) Cu content exhibit (i) X-ray amorphous structure, (ii) lower H≈11 GPa and lower ratio H³ / E*²≈0.075 GPa. A special attention was devoted to the investigation of cracking of Zr–Cu–O films under high (0.5 and 1 N) loads of the diamond indenter. The relations between the film cracking and properties of the film and the substrate were used to assess the toughness of the Zr–Cu–O film. It was found that the film toughness increase with increasing H³ / E*² ratio. It was shown that the addition of Cu to ZrO₂ film can improve its toughness.     

New Pt–Ru solid compounds as precursors of anodic catalysts for direct methanol fuel cell

This research is aimed to increase the activity of platinum–ruthenium alloy catalysts, thus to lower the catalyst loading in anodes for methanol electrooxidation. The DMFC catalyst consisting of Pt–Ru/C were prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as solid precursors at different temperatures and times of duration during their reduction. Their performances were examined by cyclic voltammograms and chronoamperometric curves. The particle size and its distribution in the catalysts were determined by means of TEM and XRD. It is found that the XRD patterns of the catalyst prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as precursors show Pt reflexions with f.c.c. crystal structure. There are diffraction peaks indicating the presence of either pure Ru or a Ru-rich h.c.p. phase, which has not been alloyed with Pt in Pt–Ru/C. The activity of the Pt–Ru/C catalysts prepared from (NH₄)₂PtCl₆ and Ru(OH)₃ as precursors is higher than those obtained from H₂PtCl₆ and RuCl₃ by chemical or thermal reduction. The activity of Pt–Ru/C catalysts prepared at 360 °C is higher than those prepared at 320 and 400 °C. After 1 h of reduction at 360 °C its particle size is small, about 7.5 nm, and its catalytic activity is higher than those obtained after 2 and 3 h of reduction.     

X-ray diffraction study on formation of ErNbO4 powder

The formation of ErNbO₄ powder, prepared by calcining an Er₂O₃ (50 mol%) and Nb₂O₅ (50 mol%) powder mixture at 1100 and 1600 °C for different durations, was investigated by using X-ray diffraction. The experimental results have displayed that although the solid-state reaction had started to some extent when the mixture was pre-calcined at 1100 °C for a duration of 13 h, the two original phases Er₂O₃ and Nb₂O₅ still dominated the mixture. When the duration of the calcination reaction was increased to 120 h at the same temperature, the resultant mixture experienced a nearly complete phase transformation. Accordingly, the ErNbO₄ phase was dominant phase in the mixture. Nevertheless, a small portion of the raw powder still existed in the mixture. When the calcining temperature was elevated to 1600 °C, ErNbO₄ powder with higher purity could be obtained for a relatively much shorter duration (only up to several tens of hours). A simple formation mechanism of ErNbO₄, an elevated-temperature-assisted solid-state chemical reaction: Er₂O₃+Nb₂O₅2ErNbO₄, is suggested. In addition, the present experimental results offer important evidence for the formation of the additional phase ErNbO₄ induced in Er:LiNbO₃ crystals by vapour transport equilibration (VTE) treatment.     

Mechanical properties and oxidation behaviour of two-phase iron aluminium alloys with Zr(Fe,Al)2 Laves phase or Zr(Fe,Al)12 τ1 phase

Two-phase Fe-rich Fe–Al–Zr alloys have been prepared consisting of binary Fe–Al with a very low solubility for Zr and the ternary Laves phase Zr(Fe,Al)₂ or τ₁ phase Zr(Fe,Al)₁₂. Yield stress, flexural fracture strain, and oxidation behaviour of these alloys have been studied in the temperature range between room temperature and 1200 °C. Both the Laves phase and the τ₁ phase act as strengthening phases increasing significantly the yield stress as well as the brittle-to-ductile transition temperature. Alloys containing disordered A2+ ordered D0₃ Fe–Al show strongly increased yield stresses compared to alloys with only A2 or D0₃ Fe–Al. The binary and ternary alloys with about 40at.% Al and 0 or 0.8at.% Zr show the effect of vacancy hardening at low temperatures which can be eliminated by heat treatments at 400 °C. At higher Zr contents this effect is lost and instead an increase of low-temperature strength is observed after the heat treatment. The increase of the high-temperature yield strength of Fe-40at.% Al by adding Zr is much stronger than by other ternary additions such as Ti, Nb, or Mo. Tests on the oxidation resistance at temperatures up to 1200 °C indicate a detrimental effect of Zr already for additions of 0.1at.%.     

Charge trapping and ac-electrical conduction in nanocrystalline erbium manganate film on Si substrate

Thin film of nanocrystalline ErMnO₃ was prepared by thermal annealing of Er–Mn oxide film deposited on p-Si(1 0 0) substrates. The X-ray fluorescence (XRF) and X-ray diffraction (XRD) technique were used to investigate the structure of the prepared Er–Mn oxide films. XRD study shows that films pre-annealed at 400 °C have amorphous structure and they were crystallised forming ErMnO₃ compound under pre-annealing at 800 °C or more. Moreover, in the prepared Er–Mn oxide films, Er oxide or Mn oxide cannot be crystallised each alone, but instead they interact chemically with each other forming ErMnO₃ compound. A comprehensive study on electrical properties was carried on. The ac-conductance and capacitance as a function of gate voltage, frequency, and temperature were studied on samples made in form of metal/oxide film/Si MOS devices. The fixed charge and interface state densities were determined and their variation with annealing process was studied and explained. It was found that the “correlated barrier hopping” CBH model controls the frequency dependence of the ac-conductivity, while Kramers–Kronig (KK) relations explain the frequency dependence of the relative permittivity. The parameters of CBH model were determined showing that the ac-conduction is realised by bipolaron hopping mechanism. dc conduction properties were also studied through the voltage and temperature dependence of the leakage dc-current density. The obtained dc-data follow a space charge limited current (SCLC) mechanism.     

Preparation of nano-sized SrAl2O4 using an amorphous hetero-nucleus complex as a precursor

Nano-crystalline SrAl₂O₄ with spinel structure was successfully prepared at 700 °C using amorphous SrAl₂(diethylenetriaminepentaacetic acid (DTPA)_1.6)(H₂O)₄ as precursor. The precursor was synthesized by a simple inorganic reaction and decomposed into SrAl₂O₄ at temperatures above 500 °C, which was proved by DTA–TGA and X-ray photoelectron spectroscopy (XPS) analysis. X-ray diffraction (XRD) results illustrated that a crystalline SrAl₂O₄ phase can form at 700 °C, which is about 600 °C lower than that used in the traditional method. The crystalline SrAl₂O₄ prepared at 900 °C for 2 h had a crystal size of about 28 nm and a grain size of about 80 nm, and its BET surface area can reach 28.056 m²/g. Calcination temperature and time had a weak effect on crystal size.     

Preparation of epitaxial and polycrystalline bismuth titanate thin films on single crystal (100) MgO by chemical solution deposition

Epitaxial and polycrystalline Bi₄Ti₃O₁₂ thin films were prepared on single crystal (100) MgO substrates by a chemical solution deposition process using metal naphthenates as starting materials. Pyrolyzed films (at 500°C) were annealed for 30 min in air at 650, 700, 750 and 800°C, respectively. The effects of annealing temperature on the crystallinity, epitaxy and surface morphology of the films were investigated by X-ray diffraction θ-2θ scans, pole-figure analysis, and atomic force microscopy (AFM). Epitaxially grown films annealed at 700 and 750°C, respectively, showed growth of three-dimensional needle-shaped grains. During annealing at 800°C, grain growth of Bi₄Ti₃O₁₂ may be suppressed by the formation of a titanium-rich phase such as Bi₂Ti₂O₇ owing to Bi volatilization, resulting in lower root mean square roughness than that of film annealed at 750°C.     

Effect of annealing on the morphology evolution and densification of LiMn2O4 film from chitosan-containing solution

Dense LiMn₂O₄ films deposited on a Pt-coated silicon substrate were obtained by annealing the deposited Li–Mn–O-chitosan films under a two-stage heat-treatment procedure. It was demonstrated that the heat-treatment at 300 °C plays an important role in the subsequent densification of LiMn₂O₄ films. This is attributed to the formation and rearrangement of the nano-sized LiMn₂O₄ crystallites. The surface morphology of the calcined Li–Mn–O-chitosan films was highly related to the annealing temperature. Ridge-like bumps formed on the surface of the films after being heated at 200 °C for 1 h. With calcination at 400 °C or higher, the surface morphology turned into a wrinkle-like microstructure. This morphology transformation is ascribed to the flowing characteristics of the Li–Mn–O-chitosan films during heat-treatment and subsequent thermal decomposition of the precursor at higher temperatures. Moreover, the electrochemical tests showed that the 700 °C-annealed LiMn₂O₄ film possesses the highest discharge capacity of 56.3 μA h/(cm² μm) and best capacity retention of 90.7% after 50 charge/discharge cycles of all annealed films.     

Microwave-assisted synthesis of CaMoO4 nano-powders by a citrate complex method and its photoluminescence property

Nano-sized CaMoO₄ powders, which have scheelite type structure, were successfully synthesized at low temperatures by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperatures from 300 to 700 °C for 3 h. Crystallizations of the CaMoO₄ nano-sized powders were detected at 400 °C, and entirely completed at a temperature of 500 °C. Almost nano-powders of CaMoO₄ heat-treated between 400 and 600 °C showed primarily spherical and homogeneous morphology. The average crystalline sizes of CaMoO₄ were 12–27 nm at temperatures of 400–700 °C, showing an ordinary tendency to increase with the temperatures. The CaMoO₄ powders prepared at 600 °C showed the strongest photoluminescence intensity.     

Synthesis, crystal structure, oxygen stoichiometry, and electrical conductivity of La1−aCaaCr0.8Ti0.2O3−δ solid solutions

Series of perovskite-type compounds La_1−aCa_aCr_0.8Ti_0.2O_3−δ (a=0–1.0) were synthesized by the ceramic technique in air (final heating 1350 °C). The crystal structure of the compounds after cooling in air to room temperature was characterized as orthorhombic in space group Pbnm. Analysis of the lattice constants shows a noticeable decrease with increasing Ca content. All compounds prepared were stable in air and in a stream of Ar/1 Pa O₂ at 20–1400 °C, as also in Ar/5% H₂ (pH₂O/pH₂=0.01) at 850–1000 °C. Oxygen stoichiometry and electrical conductivity of the solid solutions with a=0.0–1.0 are investigated. Increasing Ca contents decrease the stability of the oxides in respect to the thermal dissociation of oxygen. All compounds are p-type semiconductors in the temperature range 20–1000 °C at oxygen partial pressures of 10⁻¹⁵ to 0.21×10⁵ Pa. A maximum conductivity of about 30 S/cm in air at 1000 °C is observed for the composition with a=0.6 corresponding to a ratio of Cr³⁺/Cr⁴⁺=1 at an oxygen stoichiometry near 3.0, and oxidation states of La, Ca, Ti, and O ions of 3+, 2+, 4+, and 2−, respectively.     

Preparation and characterization of yttrium iron garnet (YIG) nanocrystalline powders by auto-combustion of nitrate-citrate gel

The nitrate–citrate gel exhibits auto-catalytic behavior, which can be used to synthesize nanocrystalline YIG powders. In this study, yttrium iron garnet (Y₃Fe₅O₁₂) nanocrystalline powders were prepared by a sol–gel auto-combustion process. The influence of metal nitrates to citric acid molar ratio (MN/CA) of the precursor solution on the combustion behavior and crystallite size of synthesized powders was investigated by scanning electron microscopy (SEM), thermal analyses (DTA/TGA) and X-ray diffraction (XRD). The results show that with increasing MN/CA value, the combustion rate increases and the single-phase YIG forms at a higher temperature. The crystallite size of the single phase YIG prepared with different MN/CA values and calcined at 800 °C for 3 h are in the range of 38–70 nm. In addition, the crystallite size of the powders increased with increasing the calcination temperature.