Enhanced dielectric properties of lead barium zirconate thin films by manganese doping

(Pb_0.5Ba_0.5)ZrO₃ (PBZ) and 1 mol% Mn-doped (Pb_0.5Ba_0.5)ZrO₃ (Mn-PBZ) sol were successfully fabricated, and corresponding thin films were deposited on Pt(1 1 1)/TiO₂/SiO₂/Si(1 0 0) substrates by spin-coating method. Effects of Mn doping on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction patterns showed that both films had a polycrystalline perovskite structure, and that the degree of (1 1 1) orientation were increased by Mn doping. Dielectric measurements illustrated that Mn-doped PBZ thin films not only had a larger dielectric constant, but also possessed a smaller dielectric loss. Accordingly, the tunability and the figure of merit of PBZ films were improved by Mn doping.     

Power-law scaling of proton conductivity in amorphous silicate thin films

Amorphous hafnium silicate, a-Hf_0.1Si_0.9O_x, thin film with thickness of 32, 41, 55, 80, 110, 120, 180 and 320 nm was prepared by multiple spin-cast process and the proton conductivity across the films was measured at intermediate temperatures (100-400 °C) in dry atmosphere. The morphologically- and compositionally-uniform films were prepared on a substrate as confirmed by SEM, RBS and XPS measurements. a-Hf_0.1Si_0.9O_x thin film clearly revealed the H/D isotope effect on ionic conductivity, indicating that protonic conduction is dominant in the measured temperature range. The films did not reveal thickness-dependent proton conductivity in dry air and the σ at given temperatures is almost constant at any thickness. No increment of σ in a-Hf_0.1Si_0.9O_x thin films by reduction of thickness might be related to the absence of the highly-conductive acid network with mesoscopically-sized length because of the relatively low concentration of Brønsted acid sites inside films.     

Effect of molecular weight on conductivity of polymer electrolytes

The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfone)imide (LiTFSI) was measured as a function of molecular weight of the PEO chains, M, over the range 0.2-5000 kg/mol. Our data are consistent with an expression σ = σ₀ + K/M proposed by Shi and Vincent [Solid State Ionics 60 (1993)] where σ₀ and K are exponential and linear functions of inverse temperature respectively. Explicit expressions for σ₀ and K are provided.     

Electrical conductivity and chemical diffusion in Perovskite-type proton conductors in H2-H2O gas mixtures

The electrical conductivities of SrZr_0.9Y_0.1O_3-δ (SZY10) and BaCe_0.95Y_0.05O_3-δ(BCY5) were measured as a function of hydrogen partial pressure P(H₂), oxygen partial pressure P(O₂), steam partial pressure P(H₂O) and temperature. Their relaxation processes were analyzed using the solution of Fick's diffusion equation to determine the chemical diffusion coefficients and surface reaction rate constants. There were the differences in chemical relaxation kinetics and the conductivity dependence on P(H₂O) between the both oxides. The chemical diffusion coefficients depend on temperature but are essentially independent of P(H₂), P(O₂) and P(H₂O). The ambipolar diffusion treatment can explain the temperature dependence of chemical diffusion coefficients quantitatively. The chemical diffusion coefficients of SZY10 is one or two order of magnitude smaller than those of BCY5 at low temperature. The sluggish conductivity relaxation in SZY10 was due to considerably small oxygen vacancy diffusion coefficients at low temperatures. The total conductivity depends on P(H₂O) in the case of SZY10, but not for BCY5. This different dependence on P(H₂O) is caused by the difference in the ratio between proton mobility and oxide-ion mobility.     

Effect of branching in base polymer on ionic conductivity in hyperbranched polymer electrolytes

Novel hyperbranched polymer, poly[bis(diethylene glycol)benzoate] capped with a 3,5-bis[(3′,6′,9′-trioxodecyl)oxy]benzoyl group (poly-Bz1a), was prepared, and its polymer electrolyte with LiN(CF₃SO₂)₂, poly-Bz1a/LiN(CF₃SO₂)₂ electrolyte, was all evaluated in thermal properties, ionic conductivity, and electrochemical stability window. The poly-Bz1a/LiN(CF₃SO₂)₂ electrolyte exhibited higher ionic conductivity compared with a polymer electrolyte based on poly[bis(diethylene glycol)benzoate] capped with an acetyl group (poly-Ac1a), and the ionic conductivity of poly-Bz1a/LiN(CF₃SO₂)₂ electrolyte was to be 7×10⁻⁴ S cm⁻¹ at 80 °C and 1×10⁻⁶ S cm⁻¹ at 30 °C, respectively. The existence of a 3,5-bis[(3′,6′,9′-trioxodecyl)oxy]benzoyl group as a branching unit present at ends in the base polymer improved significantly ionic conductivity of the hyperbranched polymer electrolytes. The polymer electrolyte exhibited the electrochemical stability window of 4.2 V at 70 °C and was stable until 300 °C.     

Effect of nitrogen doping on the thermal conductivity of GeTe thin films

The 3ω method was employed to determine the effect of nitrogen doping (5 at.%) on the thermal conductivity of sputtered thin films of stoichiometric GeTe (a material of interest for phase change memories). It was found that nitrogen doping has a detrimental effect on the thermal conductivity of GeTe in both phases, but less markedly in the amorphous (–25%) than in the crystalline one (–40%). On the opposite, no effect could be detected on the measured thermal boundary resistance between these films and SiO₂, within the experimental error. Our results agree with those obtained by molecular dynamic simulation of amorphous GeTe. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dielectric and proton conductivity studies in organic electrolytes based on 2-perfluoroalkyl-ethyl-azides

Intrinsically proton conducting organic electrolytes based on 2-perfluoroalkyl-ethyl-azides were synthesized via 1,3 cycloaddition between 2-perfluoroalkyl-ethyl-azide and alkynes. FT-IR, elemental analysis and NMR methods were used to characterize the resulting organic electrolytes. Thermal properties were analyzed with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and the morphology of the organic electrolytes was studied with X-ray diffraction (XRD). The effect of chain length on proton conductivity was investigated with impedance spectrometer. Dielectric constant and electrical modulus formalisms were analyzed and the maximum proton conductivity was measured as 10⁻² mS/cm at 180 °C.     

Effect of substrate annealing on the quality of pulsed laser deposited Zn1−xMgxO thin films

The annealing effects of sapphire substrate before deposition on the quality of epitaxial Zn_1−xMg_xO thin films grown by pulsed laser deposition are reported. Our Experimental results indicate that the surface quality of Zn_1−xMg_xO thin films and hexagonal columnar growth is improved on the annealed sapphire substrate at high temperatures due to formation of atomic terraces on the substrate surface. The photoluminescence signals also increases with the increasing annealing temperature of the substrate.     

Effect of hot pressing on the ionic conductivity of the PEO/LiCF3SO3 based electrolyte membranes

PEO/LiCF₃SO₃ (LiTFS) /Ethylene carbonate (EC) polymer electrolyte membranes were prepared with a solution casting method followed by a hot pressing process. The effect of the hot pressing process on the in-plane conductivity of the PEO electrolyte membranes was evaluated using a four-electrode AC impedance method. The composition, morphology, and microstructure of the composite polymer electrolyte were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The AC impedance measurement results indicate that the hot pressing process can increase the room temperature conductivity of the membranes 14 times to 1.7 × 10^− 3 S cm^− 1 depending upon the duration of the hot pressing process. The SEM, FTIR, XRD, and DSC results indicate that the hot pressing process could increase the amorphous part of the polymer electrolyte membrane or convert large spherulite crystals into nano-sized crystals.     

Tailoring mixed proton-electronic conductivity of BaZrO3 by Y and Pr co-doping for cathode application in protonic SOFCs

BaZr_0.8 − xPr_xY_0.2O_3 − δ (BZPYx, 0.1 ≤ x ≤ 0.4) perovskite oxides were investigated for application as cathode materials for intermediate temperature solid oxide fuel cells based on proton conducting electrolytes (protonic-SOFCs). The BZPYx reactivity with CO₂ and water vapor was evaluated by thermogravimetric and X-ray diffraction analyses, and good chemical stability was observed for each BZPYx composition. Conductivity measurements of BZPYx sintered pellets were performed as a function of temperature and p_O2 in humidified atmospheres, corresponding to cathode operating condition in protonic-SOFCs. Different conductivity values and activation energies were measured depending on the Pr content, suggesting the presence of different charge carriers. For all the compositions, the partial electronic conductivity, calculated from conductivity measurements at different p_O2, increased with increasing the temperature from 500 to 700 °C. Furthermore, the larger the Pr content, the larger the electronic conductivity. BaZr_0.7Pr_0.1Y_0.2O_3 − δ and BaZr_0.4Pr_0.4Y_0.2O_3 − δ showed mostly pure proton and electron conductivity, respectively, whereas the intermediate compositions showed mixed proton/electronic conductivity. Among the two mixed proton/electronic conductors, BaZr_0.6Pr_0.3Y_0.2O_3 − δ presented the larger conductivity, which coupled with its good chemical stability, makes this perovskite oxide a candidate cathode materials for protonic-SOFCs.     

Optimized growth and dielectric properties of barium titanate thin films on polycrystalline Ni foils

Barium titanate(BTO) thin films were deposited on polycrystalline Ni foils by using the polymer assisted deposition(PAD) technique.The growth conditions including ambient and annealing temperatures were carefully optimized based on thermal dynamic analysis to control the oxidation processing and interdiffusion.Crystal structures,surface morphologies,and dielectric performance were examined and compared for BTO thin films annealed under different temperatures.Correlations between the fabrication conditions,microstructures,and dielectric properties were discussed.BTO thin films fabricated under the optimized conditions show good crystalline structure and promising dielectric properties with εr～ 400 and tan δ < 0.025 at 100 kHz.The data demonstrate that BTO films grown on polycrystalline Ni substrates by PAD are promising in device applications.     

Effect of microstructure on the conductivity of a NASICON-type lithium ion conductor

Sintering temperature is used to control the microstructure of Li_{1 + x + y}Al_xTi_2 − xSi_yP_3 − yO₁₂ (x = 0.3, y = 0.2), a NASICON-type glass-ceramic. Scanning Electron Microscope imaging, X-Ray Diffraction, and Electrochemical Impedance Spectroscopy are employed to show that increase in sintering temperature increases conductivity while generating secondary crystalline phases. Total conductivity is as high as 3.81 × 10⁻⁴ S cm⁻¹ for sintering temperatures above 1000 °C. Crystallization of dielectric phases places the optimal sintering temperature in the 900 °C to 1000 °C range. Thermal analysis of the glass precursor reveals the glass transition, and crystallization temperatures.     

Effects of cobalt metal addition on sintering and ionic conductivity of Sm(Y)-doped ceria solid electrolyte for SOFC

The effects of cobalt addition (0.5 and 1 wt.%) on densification and ionic conductivity of Ce_0.9Sm_0.1O_1.95 (10SDC) and Ce_0.9Sm_0.075Y_0.025O_1.95 (2.5Y-SDC) have been studied. X-ray diffraction (XRD) showed that Co had changed to Co₃O₄ and Co₃O₄ + CoO after firing at 900 °C and 1300 °C respectively. The addition of Co promoted densification to occur at lower temperatures with a more uniform grain growth and greatly improved both grain boundary and bulk conductivity for 10SDC. Significant improvement of grain boundary for the 2.5Y-SDC samples was obtained, even at 1300 °C sintering, while bulk conductivity was slightly improved. Rapid grain growth along with improvement of ionic conductivity was observed when the samples were sintered further at higher temperature. Superior ionic conductivity of the 2.5Y-SDC samples with Co addition to that of the bare 10SDC suggested the potential use of Co as the co-dopant in this system to reduce the content of costly rare earth usage.     

Growth of InN thin films on ZnO substrate by plasma-assisted molecular beam epitaxy

We have studied the microstructure property of InN epitaxial films grown on ZnO substrate by plasma-assisted molecular beam epitaxy. We found that the In₂O₃ compound was produced on ZnO substrate and many pits were formed on the InN films when InN was directly grown on ZnO substrate with the N/In flux ratio less than 40. We demonstrated that the quality of InN film was significantly improved when the In₂O₃ layer was used as a buffer to prevent the reaction between In and the ZnO substrate.     

不同退火温度下氧化锌薄膜可见发光与n型导电研究

采用脉冲激光沉积法在蓝宝石衬底上制备出可见光发光良好的氧化锌薄膜, 在不同的温度下进行了后退火处理. 随着退火温度的升高, 薄膜的可见光发光发生了显著改变, 载流子浓度、迁移率、电阻率也呈现出一定的变化规律. 结合 X射线衍射、扫描电子显微镜、光致发光谱及霍尔测量, 探讨了本征氧化锌薄膜可见光发光的发射机理, 并分析了其 n型导电的原因. 关键词： 氧化锌薄膜 可见光发光 n型导电     

氩晶体薄膜法向热导率的分子动力学模拟

结合卫星“微型核”的特点，研究电介质薄膜中的导热机理以及薄膜厚度对导热系数的影响.以结构较为简单、具有可靠势能函数，实验数据较为丰富和可靠的氩的(fcc)晶体为模型,采用平衡分子动力学方法(EMD)和各向异性非平衡分子动力学方法(NEMD)计算了氩晶体及其法向薄膜的热导率,并与实验结果进行比较.模拟结果表明，氩晶体纳米薄膜的热导率显著小于对应大体积晶体的实验值，具有明显的尺寸效应.在氩薄膜厚度为2.124—5.310nm的模拟范围内,薄膜的法向热导率随着薄膜厚度的增加而呈近似线性增加. 关键词： 热导率 纳米薄膜 尺寸效应 平衡分子动力学 非平衡分子动力学     

Preparation of p-type CdS thin films and in situ dark conductivity in vacuum deposited CdS:Cu films

CdS:Cu thin films were prepared using a vacuum co-evaporation technique. The Hall measurements indicate that the conductivity characteristic of CdS thin films transformed from highly compensated in as-grown or weakly annealed materials to p-type conductive in strongly annealed materials. X-ray diffraction spectra show that as-deposited thin films were the hexagonal phase of CdS except the presence of copper for high Cu doping and the diffraction peaks of Cu disappeared after annealing. From the X-ray photoelectron spectroscopy we found the ionization of Cu atoms and the formation of an acceptor level. In situ dark conductivity in vacuum as-deposited CdS:Cu was performed in the temperature range between 27 and 250 °C. An abnormal temperature dependence of conductivity was observed in medium and heavily Cu-doped films. The formation of a p-type material at a certain temperature was also studied by the hot probe measurements, which indicates a complex compensation process in the Cu-doped CdS films.     

Effect of elaboration parameters on ionic conductivity for PECVD fuel cell electrolyte

Integration of fuel cells for nomad applications (like cell phone or notebook) is characterized by small dimensions and high performances of the component. To obtain theses properties, one of possibilities is to increase the active surface with patterned substrate. Then, the actual planar batteries must be replaced by 3D batteries. Most of deposition methods, used in the actual fuel cell process flow, are not compatible with the 3D deposition because they did not provide conformal coating. That is why we develop a PECVD electrolyte because this method is known to be compatible with 3D depositions. The PECVD electrolyte is based on a fluorocarboxylic acid, which is able to conduct protons. The obtained layer is a protonic conductor that can absorb water and stop hydrogen. Effects of elaboration parameters like pressure, power, or acid concentration on the ionic conductivity will be presented. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Effect of lanthanum substitution on the Raman spectra of barium titanate thin films

Thin films of Ba_1−xLa_xTiO₃ on platinum substrates were synthesized using the sol–gel method for x values of 0.0, 0.03, 0.05, and 0.10, and the effect of trivalent La³⁺ substitution on the structural and dielectric properties was studied. Using X‐ray diffraction, structural analysis of these compositions revealed a slight increase in the tetragonal distortion of the unit cell with increase in La content. Accordingly, an increase in the tetragonal to cubic transition temperature T_T/C was detected by temperature‐dependent Raman spectroscopy in the range of 70–500 K. Unlike the results from Raman scattering for the La‐doped BaTiO₃ films, the dielectric measurements showed broad and diffused dielectric maxima, making the estimation of the transition temperature merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of nano-SiO2 films on the electron radiation induced conductivity of polyimide

The radiation induced conductivity (RIC) behaviors in nano-SiO2 deposited polyimide (PI) were investigated using the in situ measurement technique. The results indicate that, by comparison with the case of virgin polyimide, the RIC in nano-SiO2/polyimide shows low steady state values. Moreover, the steady state RIC is a power function of the dose rate with a power index of 0.659, lower than that of 0.76 in the virgin polyimide. The interfacial barrier and trapping effects are the main reasons for the change. Meanwhile, both of the interfacial effects also result in a unipolar carrier transportation mechanism in nano-SiO2 deposited PI from the dipolar one in the virgin PI. The mechanisms of the RIC behaviors are discussed in the paper.