Dysprosium‐Doped (Ba,Sr)TiO3 Thin Films on Nickel Foilsfor Capacitor Applications

The substitution in (Ba_0.70Sr_0.30)TiO₃ thin films by the rare‐earth element dysprosium prepared at 1000°C by chemical solution deposition on nickel foils was investigated. The relatively large thermal budget applied (via annealing temperature) is shown to enhance the solubility of the Dy³⁺doping ion into the crystal lattice of the perovskite films. Preference for B‐site occupancy of this amphoteric cation was further promoted by the addition of BaO excess (1 mol%), which results in slightly larger grains in the films as observed by scanning electron microscopy. Despite this Ba‐rich composition, the presence of secondary phases in the thin films was not detected by X‐ray diffraction. Transmission electron microscopy revealed no evidence for local segregation of Dy at grain boundaries, neither the formation of NiO at the interface between the film and the metal foil was observed. The substitution of Ti⁴⁺ by Dy³⁺ leads to the formation of strong electron acceptors in the system, which balance the number of ionized oxygen vacancies arisen from the reductive crystallization atmosphere used during processing. As a consequence, the dielectric loss (tan σ) and leakage conduction measured in the resulting thin‐film capacitors were significantly reduced with respect to nominally undoped samples. The improvement of this capacitor feature, combined with the relatively high permittivities obtained in the films (490–530), shows the effectiveness of dysprosium doping within a thin‐film fabrication method for potential application into the multilayer ceramic capacitor technology.     

Effect of annealing atmosphere on leakage and dielectric characteristics of multiferroic gallium ferrite

Mutliferroic and magnetoelectric gallium ferrite (GaFeO₃) is plagued by substantial electrical leakage in polycrystalline form. Here, we report on understanding the conduction mechanism in gallium ferrite ceramic samples vis‐à‐vis processing conditions. The results show that oxygen annealed samples exhibit minimum electrical leakage as compared to air or nitrogen annealed samples suggesting the role of oxy3gen vacancies on electrical conduction. Detailed time and temperature‐dependent impedance spectroscopy analysis of the samples showed higher activation energy of conduction in oxygen annealed samples than in air or nitrogen annealed samples. The lower activation energies of 0.3‐0.4 eV in nitrogen/air annealed samples were attributed to higher oxygen vacancy concentration while oxygen annealed samples with low oxygen vacancy concentration exhibited higher activation energy of ~0.50 eV (high frequency, i.e., grain) and 0.98 eV (low frequency, i.e., grain boundary), latter due to superior level of oxygenation at the grain boundaries. Further, X‐ray photoelectron spectroscopy revealed that the oxygen vacancies are compensated by the valence fluctuation between Fe²⁺/Fe³⁺ ions whose extent is higher in air/nitrogen annealed samples than in oxygen annealed samples. The conduction mechanisms that could be active are most likely to be double ionization of oxygen vacancies and hopping from Fe²⁺ to Fe³⁺ states, latter especially in oxygen deficient samples.     

High Temperature Structural,Dielectric, and Ion Conduction Properties of Orthorhombic InVO4

Orthorhombic InVO₄ was prepared by solid‐state reaction method and characterized by powder X‐ray diffraction and scanning electron microscopy. The frequency‐dependent dielectric and conductivity properties were studied from 300 to 973 K by impedance spectroscopy. A significantly enhanced conductivity was observed at higher temperature whereas almost no conduction was observed below 723 K. Appreciable grain boundary conductivity was observed at higher temperature. The activation energies for grain and grain boundary conductivities are 0.87 and 1.28 eV, respectively. The relative permittivity of ~35 was observed in a wider range of frequencies and temperatures. The frequency dispersion dielectric studies indicated thermally activated hopping conduction process. The high temperature structural studies revealed no significant change in structural parameters except a gradual increasing trend in the unit cell parameters and amplitude of isotropic thermal parameters with increasing temperature.     

Impact of Stoichiometry on Structural and Optical Properties of Sputter Deposited Multicomponent Tellurite Glass Films

Multicomponent TeO₂–Bi₂O₃–ZnO (TBZ) glass thin films were prepared using RF magnetron sputtering under different oxygen flow rates. The influences of oxygen flow rate on the structural and optical properties of the resulting thin films were investigated. We observed that thin films sputtered in an oxygen‐rich environment are optically transparent while those sputtered in an oxygen‐deficient environment exhibit broadband absorption. The structural origin of the optical property variation was studied using X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman Spectroscopy, and transmission electron microscopy which revealed that the presence of under‐coordinated Te leads to the observed optical absorption in oxygen‐deficient films.     

Influence of grain interior and grain boundaries on transport properties of scandium-doped calcium zirconate

Calcium zirconate-based protonic conductors are currently the most promising electrolyte for high-temperature hydrogen sensors, however, protonic conductors exhibit mixed protons, oxygen vacancies and electron-holes conduction above 700°C, and the protons transport number is significantly influenced by the atmosphere. Therefore, the relationship between protons transport number and oxygen/water vapor partial pressure should be established to improve the veracity of the hydrogen sensor. Herein, CaZr_0.9Sc_0.1O_3-α perovskite oxides are prepared and the influence of grain interior and grain boundaries on transport properties is systematically investigated by using with defect chemistry theory. And the relationship between protons transport number and oxygen/water vapor partial pressure should be obtained. The results indicate that the dominant conduction carriers of CaZr_0.9Sc_0.1O_3-α were protons in Ar and reductive atmospheres at 500°C-800°C, and the conductivity () and transport number () of holes are remarkably increased with increasing oxygen partial pressure. In addition, protons, oxygen vacancies and electron-holes transport properties of grain interior and grain boundaries in scandium-doped calcium zirconate reveal that grains can effectively block oxygen vacancies transport at 550°C-800°C, but grains cannot block the holes transport. Therefore, the oxygen vacancies trend to transport through grain boundaries.     

Microstructure Evolution of In Situ Pulsed‐Laser Crystallized Pb(Zr0.52Ti0.48)O3 Thin Films

Integration of lead zirconate titanate (PZT) films with temperature‐sensitive substrates (CMOS, polymers) would benefit from growth at substrate temperatures below 400°C. In this work, in situ pulsed‐laser annealing [Rajashekhar et al. (2013) Appl. Phys. Lett., 103 [3] 032908] was used to grow crystalline lead zirconate titanate (PbZr_0.52Ti_0.48O₃) thin films at a substrate temperature of ~370°C on PbZr_0.30Ti_0.70O₃‐buffered platinized silicon substrates. Transmission electron microscopy analysis indicated that the films were well crystallized into columnar grains, but with pores segregated at the grain boundaries. Lateral densification of the grain columns was significantly improved by reducing the partial pressure of oxygen from 120 to 50 mTorr, presumably due to enhanced adatom mobility at the surface accompanying increased bombardment. It was found that varying the fractional annealing duration with respect to the deposition duration produced little effect on lateral grain growth. However, increasing the fractional annealing duration led to shift of 111 PZT X‐ray diffraction peaks to higher 2θ values, suggesting residual in‐plane tensile stresses in the films. Thermal simulations were used to understand the annealing process. Evolution of the film microstructure is described in terms of transient heating from the pulsed laser determining the nucleation events, while the energy of the arriving species dictates grain growth/coarsening.     

Structure Property Relationship in BaTiO3–Na0.5Bi0.5TiO3–Nb2O5–NiO X8R System

A novel BaTiO₃–Na_0.5Bi_0.5TiO₃–Nb₂O₅–NiO (BT‐NBT‐Nb‐Ni) system that meets the X8R specification (?55°C–150°C, ΔC/C≤±15%) of multilayer ceramic capacitors (MLCCs) was fabricated, with a maximum dielectric constant of 2350 at room temperature (25°C). Core–shell microstructure was observed by transmission electron microscopy (TEM), accounting for the good dielectric temperature stability. The role of Ni on the formation of core–shell structure and phase structure, and the subsequent relationship between structure and dielectric/ionic conduction properties were investigated. It was observed that the addition of Ni could adjust the ratio of core/shell, and significantly reduces the dielectric loss over the studied temperature range. A new Ba₁₁(Ni, Ti)₂₈O_66+x phase with a 10‐layer close‐packed structure was identified by X‐ray diffraction (XRD), serving as a source of oxygen vacancies for ionic conduction in addition to Ba(Ni,Ti)O₃. Furthermore, the impedance spectroscopy measurements demonstrated the remarkable impact of these Ni‐induced oxygen vacancies on both the grain and grain‐boundary conductivities.     

Oxygen Migration in Dense Spark Plasma Sintered Aluminum‐Doped Neodymium Silicate Apatite Electrolytes

Neodymium silicate apatites are promising intermediate temperature (500°C–700°C) electrolytes for solid oxide fuel cells. The introduction of Al promotes isotropic percolation of O^2?, and at low levels (0.83–2.0 wt% Al) enhances bulk conductivity. To better understand the effect of Al‐doping on intrinsic conductivity, and the impact of grain boundaries on the transport, dense Nd_9.33+x/3Al_xSi_6?xO₂₆ (0 ≤ x ≤ 2) pellets were prepared by spark plasma sintering. Phase purity of the products was established by powder X‐ray diffraction and the microstructure examined by scanning electron microscopy. The ionic conductivity measured by AC impedance spectroscopy for the spark plasma sintered ceramics were compared with transport in single crystals of similar composition. Intermediate Al‐doping (0.5 ≤ x ≤ 1.5) delivered superior overall conductivity for both the polycrystalline and single crystal specimens.     

Polarization Response and Thermally Stimulated Depolarization Current of BaTiO3‐based Y5V Ceramic Multilayer Capacitors

Polarization response and thermally stimulated depolarization current (TSDC) of BaTiO₃‐based ceramic multilayer capacitors with Y5V specification were studied. The temperature dependence of dielectric behavior shows that as the dc electric field increases, the polarization response in the whole measurement range (from ?125°C to +350°C) is suppressed. As the temperature rises to about 250°C, dielectric loss significantly increases and has a dependence on dc electric field, due to the leakage behavior at high temperature. According to the hysteresis loops, the calculated electrostatic energy density and energy efficiency are also closely related to polarization‐electric field. Utilizing a fixed measuring polarization condition, two TSDC relaxation peaks are observed and both are associated with oxygen vacancies. It is demonstrated that the weak peak originates from the in‐grain migration of oxygen vacancies and the strong peak with high relaxation temperature is caused by the across grain‐boundary oxygen vacancies. The activation energy estimated for the relaxation of oxygen vacancies across grain boundaries is about 0.78 eV. The main contribution for the leakage behavior is from the across grain‐boundary relaxation of oxygen vacancies. With increasing of temperature and electric field stress, the extrinsic oxygen vacancy defects show more fluent migration, which eventually leads to the resistance degradation and breakdown.     

Enhanced magnetic and dielectric properties of Ti‐doped YFeO3 ceramics

Polycrystalline YFeO₃ (YFO) and YFe_1?(4/3)xTi_xO₃(YFTO) ceramics were prepared using the powder synthesized from the sol‐gel route. X‐ray diffraction analyses of the polycrystalline ceramics revealed the crystallization of the phase in orthorhombic crystal structure associated with the space group Pnma. The magnetization versus magnetic field hysteresis loops were obtained at room temperature for YFO and YFTO ceramics. The magnetic property changes from weak ferromagnetic in YFO to ferromagnetic in YFTO ceramics. The dielectric constant recorded at room temperature for YFTO ceramics was six times higher than that of YFO, whereas the dielectric loss gets reduced to 0.06 from 0.3 for YFO at 1 kHz. Impedance spectroscopy study carried out on YFO and YFTO ceramics confirmed the existence of non‐Debye‐type relaxation. Observed single semicircle in Z′ vs ?Z′′ plot established the incidence of intrinsic (bulk) effect and ruled out any grain boundary or electrode effects. The mechanism for the dielectric relaxation and electrical conduction process observed in YFO and YFTO ceramics was discussed by invoking electric modulus formalisms. Activation energy obtained by ac conductivity study suggested that the conduction process in YFO was linked up with the existence of the polaron and oxygen vacancies, whereas only oxygen vacancies contribute to the conduction process in YFTO ceramics.     

Strong photoluminescence from N-V and Si-V in nitrogen-doped ultrananocrystalline diamond film using plasma treatment

Raman, photoluminescence, and transport properties of nitrogen-doped ultrananocrystal diamond (UNCD) films were investigated following treatment with low energy microwave plasma at room temperature. The conductivity of nitrogen-doped UNCD films treated by microwave plasma was found to decrease slightly due to the reduced grain boundaries. We speculate that the plasma generated vacancies in UNCD films and provided heat for further mobilizing the vacancies to combine with the impurities, which led to the formation of the silicon-vacancy (Si-V) and nitrogen-vacancy (N-V) defect centers. The generated color centers were found to be distributed uniformly in the samples using a PL mapping technique. The PL emitted by the plasma treated nitrogen-doped UNCD film was strongly enhanced in comparison with the untreated films.     

High thermal conductivity of spark plasma sintered silicon carbide ceramics with yttria and scandia

A fully dense SiC ceramic with a room‐temperature thermal conductivity of 262 W·(m·K)^?1 was obtained via spark plasma sintering β‐SiC powder containing 0.79 vol% Y₂O₃‐Sc₂O₃. High‐resolution transmission electron microscopy revealed two different SiC‐SiC boundaries, that is, amorphous and clean boundaries, in addition to a fully crystallized junction phase. A high thermal conductivity was attributed to a low lattice oxygen content and the presence of clean SiC‐SiC boundaries.     

Electric transport properties of rare earth doped YbxCa1-xMnO3 ceramics (part II: The role of grain boundaries and oxygen vacancies)

A comprehensive overview is provided about the role of bulk conductivity contributions in compounds of the composition Yb_xCa_1-xMnO₃ (0–10 at. % Yb-dopant concentration). For this purpose, in-situ impedance spectroscopy was successfully employed at different temperatures (−100 up to 300 °C) and frequencies (1 Hz–1 MHz). These experiments reveal the main role of grain boundaries as well as electronic and ionic contributions in conductivity. The contribution of different resistance components in electric transport properties were proposed on the base of a double-Schottky-barrier model. Migration of oxygen vacancies and their participation in conductivity were studied and the results are confirmed by observing oxygen released using a ZrO₂ oxygen sensor during dilatometry measurements in a wide range of temperatures.     

Thermal and electrical properties of nitrile‐containing polyimide/BaTiO3 composite films

Polyimide composite films were prepared by mixing the BaTiO₃ particles into poly(amic acid) solution followed by film casting and thermal imidization under controlled temperature conditions. The poly(amic acid) was synthesized by solution polycondensation reaction of 4,4′‐oxydiphthalic anhydride with 2,6‐bis(4‐aminophenoxy)benzonitrile, using N‐methyl‐2‐pyrrolidone as solvent. The surface of BaTiO₃ particles was modified by treating with an aminosilane coupling agent, 3‐aminopropyltriethoxysilane. Fourier transform infrared spectroscopy, X‐ray diffraction and scanning electron microscopy were used to characterize the structure and properties of the composites. The influence of BaTiO₃ content on the composite film properties was evidenced. The films exhibited good thermal stability having the initial decomposition temperature above 520°C. They had stable dielectric properties over large intervals of temperature and frequency. The dielectric constant and the dielectric loss increased with the increase of BaTiO₃ content. The dynamic mechanical analysis and dielectric spectroscopy revealed subglass transitions γ and β. At higher temperature an α‐relaxation that corresponds to the glass transition and a conductivity process were evidenced. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Quantification of grain boundary defect chemistry in a mixed proton-electron conducting oxide composite

Dual phase oxide membranes have shown promising hydrogen permeation fluxes in syngas applications due to their high mixed proton electron conduction (MPEC). However, the conductivity of grain boundaries can be many orders of magnitude lower than that of the bulk and so limits the total conductivity and hydrogen permeation. In this study, the three-dimensional nanoscale oxygen and cation distributions around grain and phase boundaries in a BaCe_0.8Y_0.2O_3-δ-Ce_0.8Y_0.2O_2-δ (BCY-YDC) membrane were quantified by atom probe tomography (APT) and related to average grain boundary conductivity measured by electrochemical impedance spectroscopy (EIS). Segregation varied among the general high-angle grain boundaries analyzed, but no trend from orientation analysis was determined. Correlative APT and electron energy loss spectroscopy (EELS) of one YDC grain boundary revealed composition and cerium valence information, respectively, allowing for the determination of vacancies at the grain boundary. While a specific MPEC membrane is characterized, the results are relevant to proton and electron conduction in a number of technologically important ceramics.     

Annealing effect on relaxor behaviours of spark plasma sintered Pb(Sc1/2Nb1/2)O3 superfine ceramics

Abstract

Abstract

Relaxor ferroelectric Pb(Sc_1/2Nb_1/2)O₃ (PSN) superfine ceramics were fabricated by spark plasma sintering process and subjected to an annealing in oxygen ambience at a low temperature of 500°C. The microstructure of the PSN ceramics was examined by X‐ray diffraction and scanning and transmission electron microscopy, while the dielectric properties were measured in the range of 25–200°C. The dielectric measurements revealed a reverse change in the frequency dispersion ΔT and diffusive factor λ as annealing extended. Transmission electron microscopy observation and conductivity measurement revealed that the uncommon performance in relaxor properties could be attributed to the complex effects of oxygen vacancies and domain structures induced by the annealing.     

Polycarbazole obtained by electrochemical polymerization of monomers either in solution or in thin film form

Polycarbazole has been synthesized by electrochemistry. The carbazole monomer source consists either in carbazole in solution in the electrolyte or in carbazole deposited in thin film form onto the working electrode. The two families of polymers have been studied by infrared absorption, X‐ray diffraction, thermal gravimetric analysis, scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy, electron spin resonance, and electrical conductivity measurements. It is shown that the polycarbazole films obtained with carbazole deposited in the thin film form exhibit a better polymerization efficiency and an electrical conductivity one order of magnitude higher. This result is in good accordance with a higher spin density and homogeneity. It is proposed that not only are some monomers activated during the evaporation but also that the physical contact between the working electrode and the continuous carbazole films induces the growth of homogenous highly polymerized polycarbazole films. In agreement with this suggestion, the SEM study shows that this type of polycarbazole thin films keep in memory the morphology of the SnO₂ under layer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1561–1568, 2000     

Electron-beam damage and point defects near grain boundaries in cerium oxide

Cerium oxide is a technologically important ceramic with applications in catalysis and potentially as an electrolyte for solid-oxide fuel cells (SOFCs). The technological interest is largely due to the behavior of oxygen vacancies in this material. Grain boundaries play an important role in oxygen vacancy diffusion and, although not completely understood, the influence of grain boundaries has been attributed to both a space-charge effect and the segregation of impurities. In this paper, results from spatially resolved electron-energy-loss spectroscopy (EELS) near grain boundaries in doped CeO₂ in a transmission electron microscope (TEM) are reported. The data are interpreted as the result of beam damage that varies as the electron beam is scanned across grain boundaries and suggest a spatially varying concentration of oxygen vacancies near the grain boundaries.     

A Layered Perovskite EuBaCo2O5+δ for Intermediate‐Temperature Solid Oxide Fuel Cell Cathode

A layered perovskite EuBaCo₂O_5+δ (EBCO) has been prepared by a solid‐state reaction, and evaluated as potential cathode for intermediate‐temperature solid oxide fuel cells. Structural characterizations are determined at room temperature using powder X‐ray diffraction and transmission electron microscopy technique. The good fits to the XRD data by Rietveld refinement method are obtained in the orthorhombic space group (Pmmm). The lower average thermal expansion coefficient, 14.9 × 10^–6 °C^–1 between 100 and 800 °C, indicates its better thermal expansion compatibility with conventional electrolytes, compared with the other cobalt‐containing cathode materials. The high electrical conductivity and large oxygen nonstoichiometry at intermediate temperatures suggest the effective charge transfer reactions including electron conduction and oxide‐ion motion in cathode. As a result, a highly electrochemical activity towards the oxygen reduction reaction is achieved between 600 and 700 °C, as evidenced by low area‐specific resistances, e.g. 0.14–0.5 Ω cm². In addition, cathodic overpotential and oxygen reduction kinetics of the EBCO cathode have also been studied.     

Structural,morphological and electrical properties of Ce1−xRuxO2−δ (x=0.005–0.02) solid solutions

Nanoparticles of ceria–ruthenium oxide solid solutions with composition Ce_1−xRu_xO_2−δ (x=0.005–0.02) were successfully produced by self–propagating room temperature synthesis using reaction between metal nitrates and sodium hydroxide. These compositions were characterized by X–ray powder diffraction (XRD), Raman spectroscopy, specific surface area, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X–ray spectroscopy (EDX). The experimental measurements were complemented by calculations based on the ion–packing model. XRD analysis revealed the presence of single–phase solid solutions with CeO₂ fluorite structure (regardless of dopants concentration) and Raman spectroscopy confirmed the presence of the RuO₂ phase. Electrochemical impedance spectroscopy (EIS) measurements of sintered samples at different temperatures showed that the small ionic radius dopant reduces oxygen vacancies mobility that is responsible for the conductivity of these ceramics.