Ultra-thin nanocrystalline lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.8Fe0.2O3−δ) films synthesis by RF-sputtering and temperature-dependent conductivity studies

Nanocrystalline lanthanum strontium cobalt ferrite (LSCF) ultra-thin films with high in-plane electrical conductivity have been deposited by RF sputtering from composite targets. The films, with nominal thickness of 54 nm, are crystalline when annealed or deposited at temperatures above 450 °C. Effects of annealing temperature, annealing time, and substrate temperature on crystallization, microstructure, and room temperature lateral electrical conductivity have been systematically studied. No interfacial reaction products between the LSCF and single crystalline yttria-stabilized zirconia (YSZ) were observed from X-ray diffraction studies upon annealing until 750 °C. In-plane electrical conductivity as high as 580 S cm⁻¹ at 650 °C has been observed for LSCF thin films deposited on single crystalline YSZ substrates and sputtered nanocrystalline YSZ thin films; while activation energy for conductivity were determined to be 0.15 eV and 0.10 eV for the former and latter films, respectively, in 650–400 °C range. The high in-plane electrical conductivity for the nanocrystalline LSCF ultra-thin films is likely attributed to their low level of porosity. Micro-solid oxide fuels cells using 15 nm thick LSCF films as cathodes and sub-100 nm yttria-doped zirconia thin film electrolytes have been fabricated successfully and demonstrated to achieve peak power density of 60 mW cm⁻² at 500 °C. Our results demonstrate that RF sputtering provides a low-temperature synthesis route for realizing ultra-thin nanocrystalline LSCF films as cathodes for intermediate- or low-temperature solid oxide fuel cells.     

Ionic conducting behavior of solvent-free polymer electrolytes prepared from oxetane derivative with nitrile group

Polymer with trimethylene oxide (TMO) units prepared from ring-opening polymerization of an oxetane derivative is a candidate for the matrix of solid polymer electrolytes. We prepare an oxetane derivative with nitrile group, 3-(2-cyanoethoxymethyl)-3-ethyloxetane, CYAMEO. CYAMEO is polymerized by using a cationic initiator system. The structure of the resulted polymer, P(CYAMEO), is confirmed by NMR and FTIR spectroscopic techniques. Inorganic salts, such as lithium salts, can be dissolved in P(CYAMEO) matrix. FTIR and DSC results of P(CYAMEO)-based electrolyte films suggest that lithium ions in the P(CYAMEO) matrix interact with the nitrile side chains, mainly, and not with the oxygen atoms on the main chain of the P(CYAMEO). The conductivity at 30 °C for P(CYAMEO)-based electrolyte films, P(CYAME)10(LiX)1, is 19.6 μS cm⁻¹ (X = LiClO₄), 6.59 μS cm⁻¹ (BF₄), 6.54 μS cm⁻¹ (CF₃SO₃), and 25.0 μS cm⁻¹ (N(CF₃SO₂)₂). The rise in temperature from 30 °C to 70 °C increases their conductivity, about 30-40 times. The conductivity at 70 °C for P(CYAMEO)-based electrolyte films is 0.742 mS cm⁻¹ (X = LiClO₄) and 0.703 mS cm⁻¹ (N(CF₃SO₂)₂). Electrochemical deposition and dissolution of lithium on a nickel plate electrode are observed in the solvent-free three-electrode electrochemical cell with P(CYAMEO)10(LiX)1, (X = ClO₄ or N(CF₃SO₂)₂) electrolyte film at 55 °C.     

Highly stable transparent and conducting gallium-doped zinc oxide thin films for photovoltaic applications

Transparent and highly conducting gallium zinc oxide (GZO) films were successfully deposited by RF sputtering at room temperature. A lowest resistivity of ∼2.8×10⁻⁴ Ω cm was achieved for a film thickness of 1100 nm (sheet resistance ∼2.5 Ω/□), with a Hall mobility of 18 cm²/V s and a carrier concentration of 1.3×10²¹ cm⁻³. The films are polycrystalline with a hexagonal structure having a strong crystallographic c-axis orientation. A linear dependence between the mobility and the crystallite size was obtained. The films are highly transparent (between 80% and 90% including the glass substrate) in the visible spectra with a refractive index of about 2, very similar to the value reported for the bulk material. These films were applied to single glass/TCO/pin hydrogenated amorphous silicon solar cells as front layer contact, leading to solar cells with efficiencies of about 9.52%. With the optimized deposition conditions, GZO films were also deposited on polymer (PEN) substrates and the obtained results are discussed.     

Electrochemical properties of Li1.4Al0.4Ti1.6(PO4)3 synthesized by a co-precipitation method

Sub-micron Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP) ceramic powder is synthesized by a co-precipitation method which can be applied for mass production. A pure Nasicon phase is confirmed by X-ray diffraction analysis and the primary particle size of the product is 200-500 nm. The sinterability of LATP is investigated and the relative density of 97% reached at a sintering temperature as low as 900 °C for 6 h. The bulk lithium ionic conductivity of the sintered pellet is 2.19 × 10⁻³ S cm⁻¹, and a total conductivity of 1.83 × 10⁻⁴ S cm⁻¹ is obtained.     

The influence of the nitrogen-ion flux on structure and ionic conductivity of vapor deposited lithium phosphorus oxynitride films

Thin films of lithium phosphorus oxynitride (Lipon) have been grown using a plasma-assisted, directed vapor deposition (PA-DVD) technique. In this approach, a high voltage electron beam is used to vaporize a Li₃PO₄ source and a supersonic, nitrogen-doped, helium gas jet then transport the vapor towards a substrate. A hollow cathode technique was then used to create an argon plasma just above the substrate. This sufficiently ionized the nitrogen in the gas jet to allow its incorporation into the Li₃PO₄ film reactively forming lithium phosphorus oxynitride. Increasing the nitrogen flux in the gas jet also increased the deposition rate from 113 to 178 nm min⁻¹ for the deposition conditions used here, significantly reduced the pore volume fraction in the films and increased the N/P ratio from 0 to 0.75 as the gas jet nitrogen flux was increased from zero to 4.3 × 10¹⁸ molecules cm⁻² s⁻¹. Using substrate rotation, pore and columnar-free dense Lipon films could be grown by this method. The Li-ion conductivity increased from 3.7 × 10⁻⁹ to 5.2 × 10⁻⁷ S cm⁻¹ as the nitrogen concentration was increased from zero to 2.1 × 10¹⁸ molecules cm⁻² s⁻¹ and was correlated with an increase in the film's Li/P ratio. An optimum nitrogen flux has been identified. As the nitrogen flux was increased above this value, the Lipon films suffered lithium loss and partial crystallization, resulting in a decrease in their Li-ion conductivity.     

Electrical properties of a-Si:H thin films as a function of bonding configuration

Hydrogenated amorphous silicon (a-Si:H) thin films were fabricated by Radio Frequency (RF) magnetron sputtering. For solar-cell applications, a-Si:H layers are required to show low dark conductivity and high photoconductivity and, thus, high photosensitivity. Hydrogen flow ratio and working pressure were mainly adjusted to control bonding configurations and hydrogen concentration in the films. At a high working pressure of 12 mTorr, all of the prepared amorphous and microcrystalline silicon films showed a dominant IR absorption peak at 2100 cm⁻¹, which indicates a Si-H₂ stretching mode, grain boundaries and microvoids. When the working pressure was decreased to as low as 3 mTorr with a hydrogen flow ratio of 0.1, the bonding configuration of the films was mainly Si-H as determined by the dominant IR absorption peak at 2000 cm^−1, and the photosensitivity of the films was maximized to 760.     

Preparation and performance of novel Li–Ti–Si–P–O–N thin-film electrolyte for thin-film lithium batteries

Novel Li–Ti–Si–P–O–N thin-film electrolyte was successfully fabricated by RF magnetron sputtering from a Li–Ti–Si–P–O target in N₂ atmosphere at various temperatures. XRD, SEM, EDX, XPS, and EIS were employed to characterize their structure, morphology, composition and electrochemical performances. The films were smooth, dense, uniform, without cracks or voids, and possessed an amorphous structure. Their room temperature lithium-ion conductivities were measured to be from 3.6 × 10⁻⁷ S cm⁻¹ to 9.2 × 10⁻⁶ S cm⁻¹, and the temperature dependence of the ionic conductivities fits the Arrhenius relation. This kind of electrolyte possessed good properties is a promising candidate material for solid-state thin-film lithium batteries.     

RF sputtered wide work function indium molybdenum oxide thin films for solar cell applications

Indium molybdenum oxide (IMO) thin films were deposited by RF magnetron sputtering on glass substrates at room temperature. The deposition and argon partial pressures were maintained at 6.0 × 10⁻¹ Pa and 3.0 × 10⁻¹ Pa, respectively. The oxygen partial pressure (OPP) was varied in the range 1.0-6.0 × 10⁻³ Pa. The films were sputtered at 40 W for 30 min using the target consisted In₂O₃ (98 wt%): Mo (2 wt%). The films are polycrystalline with a slight preferential orientation along (2 2 2) plane. The crystallinity is increased with the increasing OPP. The negative sign of Hall coefficient confirmed the n-type conductivity. A maximum mobility ∼19 cm² V⁻¹ s⁻¹ is obtained for the films deposited with OPP of 3.6 × 10⁻³ Pa. The average visible transmittance calculated in the wavelength ranging 500-800 nm is ranging between 2% and 77%. The optical band gap calculated from the absorption data is varied between 3.69 and 3.91 eV. A striking feature is that the work function of the films is wide ranging 4.61-4.93 eV. A possibility of using the produced IMO films as transparent conducting oxide in photovoltaic applications such as organic solar cells is discussed in this article.     

Percolated interface conductivity of sheet-like electrolyte prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid)-deposited core-shell particles and effect of core particle size

Proton conducting poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) ultrathin layer was deposited on sol-gel-derived phenylsilsesquioxane (PhSiO_3/2) particles via layer-by-layer (LbL) assembly technique. Spherical and size-controlled particles in the range of 0.3-4.0 μm were successfully prepared by varying the condensation reaction. One PAMPS layer with 1.5 nm thickness was deposited on the particle, the volume fractions of Primer/PAMPS-multilayer varied from 0.7 to 11 vol.%. Sheet-like composite electrolytes in which PAMPS layer percolated throughout the sample can be obtained by hot-pressing the PAMPS-deposited PhSiO_3/2 particles. The sample prepared using unmodified PhSiO_3/2 exhibited a very low proton conductivity of 10⁻⁹ S cm⁻¹ at 80 °C, whereas the conductivity of the composite electrolytes increased significantly with a very small amount of PAMPS-multilayer (∼1 vol.%). The composite with 11 vol.% PAMPS exhibited 2 × 10⁻³ S cm⁻¹ at 80 °C and 95% of relative humidity.     

Enhanced conductivity and stability of composite membranes based on poly (2,5-benzimidazole) and zirconium oxide nanoparticles for fuel cells

Poly (2,5-benzimidazole) (ABPBI) and zirconium oxide (ZrO₂) nanoparticles composite membranes were synthesized. These membranes can be fabricated into tough, dense membranes by blending Poly (2,5-benzimidazole) (ABPBI) with zirconium oxide (ZrO₂) nanoparticles, which were characterized by using FTIR, XRD, SEM, TGA, DSC and tensile test. These composite membranes showed increased conductivity compared with original ABPBI membrane. Maximum proton conductivity at 100 °C was found to be 0.069 S cm⁻¹ on 10% ZrO₂ incorporated ABPBI composite membrane, almost four times as high as the 0.018 S cm⁻¹ obtained in the case of the ABPBI membrane. The conductivity was 0.0325 S cm⁻¹ at 180 °C in dry condition for ABPBI with 10% ZrO₂ nanoparticles composite membrane, higher than the conductivity 0.011 S cm⁻¹ of the ABPBI membrane at same condition. Furthermore, the composite membranes were shown to have high thermal and mechanical stability. These results suggest that ABPBI/ZrO₂ composite membranes may be a promising polymer electrolyte for fuel cells at medium or high temperature, due to their strong physical properties.     

The effect of sorbitol on the morphological characteristics of lead–tin films electrodeposited from an alkaline bath

An alkaline Pb–Sn plating bath containing sorbitol as additive has been developed, which has the advantage of low toxicity and ease of handling relative to fluoborate baths, etc. The Pb–Sn deposition voltammetric curve from this bath revealed two deposition processes, at −0.87 and −1.17 V. The voltammetric studies at various sweep rates indicate that the Pb–Sn deposition process is controlled by mass transport. The joint diffusion coefficient of the Pb(II) and Sn(II) sorbitate complex species is 1.15 × 10⁻⁶ cm² s⁻¹. SEM analysis showed that the films produced at −0.87 and −1.17 V are, respectively, composed of dendritic or hexagonal crystals, showing that co-deposition of tin hindered dendritic growth. EDS of the Pb–Sn films showed that the deposit obtained at −0.87 V is pure lead, while that at −1.17 V, with 5.0 or 10.0 C cm⁻², has 19.10 wt% Sn or 26.35 wt% Sn, respectively. It was observed that the Pb–Sn electrodeposited films were grey at both deposition potentials (−0.87 and −1.17 V) and deposition charges (5.0 and 10.0 C cm⁻²). X-ray spectra showed that at the potential −0.87 V a mixture of Pb, PbPt₄ and Pb₂PtO₄ were deposited, while at −1.17 V, Pb, β-Sn, and PbSnO₃ were deposited.     

I-V characteristics of a-Si-c-Si hetero-junction diodes made by hot wire CVD

p-Type hydrogenated amorphous silicon (a-Si:H) was deposited on n-type crystalline silicon (c-Si) substrates to obtain hetero-junction diodes. Additionally, a thin intrinsic a-Si:H layer was inserted between both the p-type film and the n-type substrate to study its passivation effect on the c-Si surface. The amorphous films were obtained by the hot wire chemical vapor deposition (HWCVD) technique, using a tungsten filament and silane (SiH₄), hydrogen (H₂) and diborane (B₂H₆) gases, where the deposition parameters such as gas flow, substrate temperature and filament temperature were varied. Optical band gap, deposition rate and conductivity were measured for all the films. We studied the influence of the quality of the amorphous films upon the performance of the hetero-junction diodes. In particular, the diode ideality factor (n) and the saturation current density (J₀) were determined by measuring the current-voltage characteristics in dark conditions. It is shown that the presence of the intrinsic layer is fundamental for making good diodes, since devices made without this film cause the diodes to have high saturation current density and ideality factor (J₀>10×10⁻⁶ A/cm², n>4) as compared to diodes with a good intrinsic layer (J₀=5×10⁻⁹ A/cm², n=1.39). The results obtained are encouraging, but the quality of the intrinsic films still should be improved for applying them to HIT solar cells.     

Covalent-ionically cross-linked polyetheretherketone proton exchange membrane for direct methanol fuel cell

In this paper, the proton exchange membrane prepared by covalent-ionically cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent-ionically cross-linked PEEK-WC membrane reaches to 2.1 × 10⁻² S cm⁻¹ at room temperature and 4.1 × 10⁻² S cm⁻¹ at 80 °C. The methanol permeability is 1.3 × 10⁻⁷ cm² s⁻¹, 10 times lower than that of Nafion^® 117 membrane. The results suggest that the covalent-ionically cross-linked PEEK-WC membrane is a promising candidate for direct methanol fuel cell because of low methanol permeability and adequate proton conductivity.     

Poly(arylene ether)s with pendant sulfoalkoxy groups prepared by direct copolymerization method for proton exchange membranes

A novel sulfonated monomer sodium-3-(4-(2,6-difluorobenzoyl)phenoxy)propane-1-sulfonate was designed and synthesized. Based on above monomer, a series of sulfonated poly(arylene ether) copolymers containing aliphatic acid groups between aromatic backbones and sulfonic acid groups (PSOA-SPAE) were successfully prepared by direct copolymerization. Ion exchange capacity (IEC) of the copolymers could be mediated in the range of 1.07–1.61 meq g⁻¹ by the monomer ratios used in the copolymerization. These copolymers exhibited good oxidative and dimensional stability. The proton conductivities of copolymer films increased with the increase of IEC and temperature. The conductivity of PSOA-SPAE-80 was 4.94 × 10⁻² S cm⁻¹ at room temperature, and was up to 1.35 × 10⁻¹ S cm⁻¹ at 100 °C, which was close to that of Nafion 117. These copolymers may be promising proton exchange membranes (PEMs) due to their high proton conductivity and good oxidative and dimensional stability.     

Doping effects on complex perovskite Ba3Ca1.18Nb1.82O9−δ intermediate temperature proton conductor

In this work, the effects of Ce doping on the Ca and Nb ions in complex perovskite Ba₃Ca_1.18Nb_1.82O_9−δ (BCN18) proton conductor have been evaluated. It has been found that cerium ions can be doped into both the Ca and Nb sites to form a single-phase complex perovskite structure when the sintering temperature is 1550 °C. Ce ions substituted with Nb ions enhances the electrical conductivity, especially the grain boundary conductivity. The highest conductivity has been obtained for a composition of Ba₃Ca_1.18Nb_1.62Ce_0.2O_9−δ, possessing a conductivity of 2.69 × 10⁻³ S cm⁻¹ at 550 °C in wet H₂, a 78% enhancement compared with BCN18 (1.51 × 10⁻³ S cm⁻¹). The chemical stability tests show that Ce-doped BCN18 samples remain single phase after treated either in boiling water for 7 h or in pure CO₂ for 4 h at 700 °C. This work has demonstrated a new direction in developing intermediate temperature proton conducting materials that possess both high conductivity and good stability.     

Effects of substrate temperature on the properties of facing-target sputtered Al-doped ZnO films

ZnO:Al films (Al 2.5 wt%) were deposited using a DC facing targets magnetron sputtering via two ZnO targets mixed with Al₂O₃. The structural, electrical and optical properties of the deposited films were strongly influenced by substrate temperature. Films with better texture, higher transmission, lower resistivity and larger carrier concentration were obtained for the samples fabricated at higher substrate temperature. The optimal condition for deposition of ZnO:Al film with the lowest resistivity of 3.18×10⁻⁴ Ω cm, the highest carrier concentration of 4.58×10²⁰ cm⁻³, and a transmission toward 85% in the visible range was obtained at 200 °C. This film proposes a promising future for the application of the practical window and contact layers for solar cells.     

Zirconium phosphate as the proton conducting material in direct hydrocarbon polymer electrolyte membrane fuel cells operating above the boiling point of water

Zirconium phosphate (ZrP) was investigated as a possible proton conductor material in direct hydrocarbon polymer electrolyte membrane (PEM) fuel cells that operate at greater temperatures than conventional PEM fuel cells. Amorphous zirconium phosphate was synthesized in this work by precipitation at room temperature via reaction of ZrOCl₂ with H₃PO₄ aqueous solutions. The conductivity of the synthesized ZrP materials were 7.04 × 10⁻⁵ S cm⁻¹ for ZrP oven dried in laboratory air at 70 °C and 3.57 × 10⁻⁴ S cm⁻¹ for ZrP powder dried first at 70 °C in laboratory air and then processed at 200 °C with continuous H₂O injection at an H₂O/N₂ molar ratio of 6. This work showed that by maintaining appropriate water content in the vapour phase at processing conditions, it was possible to alter the composition of zirconium phosphate to a sufficiently hydrated state, and thereby avoid the normal decrease in conductivity with increasing temperature.     

Synthesis and characterization of lanthanum silicate apatite by gel-casting route as electrolytes for solid oxide fuel cells

Lanthanum silicate oxyapatite, La₁₀Si₆O₂₇ is successfully synthesized by a water-based gel-casting technique. The effect of calcination and sintering temperatures on the conductivity is investigated in detail in the temperature range between 300 and 800 °C by the impedance spectroscopy. The highest oxygen ion conductivity is 1.50 × 10⁻³ S cm⁻¹ at 500 °C and 3.46 × 10⁻² S cm⁻¹ at 800 °C for an apatite electrolyte sintered at 1650 °C, which is one order of magnitude higher than that synthesized by the conventional solid state reaction route under the same sintering conditions. The thermal expansion coefficient (TEC) of the as-synthesized apatite is 9.7 × 10⁻⁶ K⁻¹. A solid oxide fuel cell using La₁₀Si₆O₂₇ as an electrolyte shows an open circuit potential of 1.06 V and power output of 7.89 mW cm⁻² at 800 °C. The results demonstrate the potential of the silicate oxyapatite materials synthesized by the gel-casting as an alternative electrolyte in solid oxide fuel cells.     

Morphology and electrical properties of conductive carbon coatings for cathode materials

Many interesting cathode materials, such as LiFePO₄, LiMnPO₄, LiFeBO₃ or the recently discovered Li₂FeSiO₄ and Li₂MnSiO₄, exhibit extremely low electronic conductivity (<10⁻⁹ S cm⁻¹). A very efficient way for improving the electronic transport in such materials is supposed to be the preparation of carbon coatings around individual active particles. Despite the increasing number of reports on preparation of various carbon coatings, neither the formation mechanism nor the detailed coating properties have been explained satisfactorily. The present paper is an attempt to find a clear correlation between the synthesis parameters, the resulting coating morphology and, finally, its electrical properties. As a substrate material for deposition of coatings, more or less monodisperse TiO₂ particles in various sizes were used. As a carbon precursor, citrate was used because it had given excellent results in our previous investigation of the LiFePO₄ system. It is shown that citrate precursor delivers pretty good conductivity (ca. 30 S cm⁻¹) after a 10 h heat treatment at 700 °C or higher. The conductivity percolation threshold can be reached already at 1.5 vol.% of carbon, while the plateau conductivity of the whole composite is about 0.1 S cm⁻¹. At that level, the carbon phase is supposed to form a well-distributed 3D electrical network within the composite.     

Synthesis of poly(arylene ether sulfone)s with locally and densely sulfonated pentiptycene pendants as highly conductive polymer electrolyte membranes

Poly(aryl ether sulfone)s containing sulfonated pentiptycene groups SPES-x-PPD are firstly synthesized through nucleophilic aromatic substitution polycondensation by using pentiptycene-6,13-diol, bis(4-hydroxyphenyl) sulfone and 4,4′-difluorodiphenyl sulfone, followed by postsulfonation with concentrated sulfuric acid at room temperature. The structures of SPES-x-PPD are characterized by IR, ¹H NMR and ¹³C NMR spectra. These ionomers generally show high thermal stability. Transmission electron microscopic observations reveal that SPES-x-PPD membranes form well-defined microphase separated structures. SPES-40-PPD with the IEC value 2.36 mmol g⁻¹ shows conductivity of 2.6 × 10⁻¹ S cm⁻¹ which is much higher than that of perfluorinated Nafion 117 membrane (1.1 × 10⁻¹ S cm⁻¹) at 80 °C and 94% RH. At 80 °C and 34% RH, SPES-40-PPD membrane displays the conductivity of 2.7 × 10⁻³ S cm⁻¹ which is comparable with that of Nafion 117 membrane (3.0 × 10⁻³ S cm⁻¹).