Extremely High Silver Ionic Conductivity in Composites of Silver Halide (AgBr,AgI) and Mesoporous Alumina

The silver ionic conductivity in heterogeneous systems of AgBr:Al₂O₃ and AgI:Al₂O₃ is highly enhanced by utilizing mesoporous Al₂O₃ as the insulating phase. The highest Ag⁺ conductivity of 3.1 × 10^–3 Ω^–1 cm^–1 (at 25 °C) has been obtained for the AgI:Al₂O₃ composite with an Al₂O₃ volume fraction of 0.3. For AgBr:Al₂O₃, the enhancement of the conductivity is satisfactorily explained in the framework of the ideal space‐charge model, while in the case of AgI:Al₂O₃ stacking disorder is also considered to contribute to the ionic conductivity.     

Nanoengineered Polypyrrole‐Coated Fe2O3@C Multifunctional Composites with an Improved Cycle Stability as Lithium‐Ion Anodes

Novel multifunctional composites composed of highly dispersed nanosized Fe₂O₃ particles, a tubular mesoporous carbon host, and a conductive polypyrrole (PPy) sealing layer are hierarchically assembled via two facile processes, including bottom‐up introduction of Fe₂O₃ nanoparticles in tubular mesoporous carbons, followed by in situ surface sealing with the PPy coating. Fe₂O₃ particles are well‐dispersed within the carbon matrix and PPy is spatially and selectively coated onto the external surface and the pore entrances of the Fe₂O₃@C composite, thereby bridging the composite particles together into a larger unit. As an anode material for Li‐ion batteries (LIBs), the PPy‐coated Fe₂O₃@C composite exhibits stable cycle performance. Additionally, the PPy‐coated Fe₂O₃@C composite also possesses fast electrode reaction kinetics, high Fe₂O₃ use efficiency, and large volumetric capacity. The excellent electrochemical performance is associated with a synergistic effect of the highly porous carbon matrix and the conducting PPy sealing layer. Such multifunctional configuration prevents the aggregation of NPs and maintains the structural integrity of active materials, in addition to effectively enhancing the electronic conductivity and warranting the stability of as‐formed solid electrolyte interface (SEI) films. This nanoengineering strategy might open new avenues for the design of other multifunctional composite architectures as electrode materials in order to achieve high‐performance LIBs.     

Fabrication and Electrochemical Properties of Epitaxial Samarium‐Doped Ceria Films on SrTiO3‐Buffered MgO Substrates

Thin films of samarium‐oxide‐doped (20 mol%) ceria (SDC) are grown by pulsed‐laser deposition (PLD) on (001) MgO single‐crystal substrates. SrTiO₃ (STO) prepared by PLD is used as a buffer layer on the MgO substrates to enable epitaxial growth of the fluorite‐structured SDC film; the STO layer provides a proper crystalline match between SDC and MgO, resulting in highly crystalline, epitaxial SDC films grown in the (001) orientation. Film conductivity is evaluated by electrochemical impedance spectroscopy measurements, which are performed at various temperatures (400–775 °C) in a wide range of oxygen partial pressure (pO₂) values (10^?25?1 atm) in order to separate ionic and electronic conductivity contributions. At 700 °C, SDC/STO films on (100) MgO exhibit a dominant ionic conductivity of about 7 × 10^?2 S cm^?1, down to pO₂ values of about 10^?15 atm. The absence of grain boundaries make the SDC/STO/MgO heterostructures stable to oxidation‐reduction cycles at high temperatures, in contrast to that observed for the more disordered SDC/STO films, which degraded after hydrogen exposure.     

The Effects of Multiphase Formation on Strain Relaxation and Magnetization in Multiferroic BiFeO3 Thin Films

Multiferroic epitaxial Bi‐Fe‐O thin films of different thicknesses (15–500 nm) were grown on SrTiO₃ (001) substrates by pulsed laser deposition under various oxygen partial pressures to investigate the microstructural evolution in the Bi‐Fe‐O system and its effect on misfit strain relaxation and on the magnetic properties of the films. Films grown at low oxygen partial pressure show the canted antiferromagnetic phase α‐Fe₂O₃ embedded in a matrix of BiFeO₃. The ferromagnetic phase, γ‐Fe₂O₃ is found to precipitate inside the α‐Fe₂O₃ grains. The formation of these phases changes the magnetic properties of the films and the misfit strain relaxation mechanism. The multiphase films exhibit both highly strained and fully relaxed BiFeO₃ regions in the same film. The magnetization in the multiphase Bi‐Fe‐O films is controlled by the presence of the γ‐Fe₂O₃ phase rather than heteroepitaxial strain as it is the case in pure single phase BiFeO₃. Also, our results show that this unique accommodation of misfit strain by the formation of α‐Fe₂O₃ gives rise to significant enhancement of the piezo electric properties of BiFeO_3.     

Electrical Transport and Oxygen Exchange in the Superoxides of Potassium,Rubidium, and Cesium

Conductivity, ionic transference number, and chemical diffusion coefficients are determined for KO₂, RbO₂, and CsO₂. Based on such results, a defect‐chemical model is constructed. These superoxides are found to exhibit a total conductivity in the range of 3 × 10^–7 to 5 × 10^–5 S cm^–1 at 200 °C with contributions from ionic and electronic carriers. The ionic conductivity is caused by alkali interstitials and superoxide vacancies as mobile defects, and is found to exceed the n‐type electronic conductivity. ¹⁸O isotope exchange on powder samples (monitoring the gas phase composition) shows that essentially all oxygen can be exchanged. At high pO₂ this largely occurs without breaking of the O–O bond—indicating a sufficient mobility of molecular superoxide species in the solid—and with an effective rate constant that is much higher than for other large‐bandgap mixed conducting materials such as SrTiO₃.     

An All‐Ceramic Solid‐State Rechargeable Na+‐Battery Operated at Intermediate Temperatures

A major challenge to the development of the next‐generation all‐solid‐state rechargeable battery technology is the inferior performance caused by insufficient ionic conductivity in the electrolyte and poor mixed ionic‐electronic conductivity in the electrodes. Here we demonstrate the utility of elevated temperature as an advantageous means of enhancing the conductivity in the electrolyte and promoting the catalytic activity at electrodes in an all‐ceramic rechargeable Na⁺‐battery. The new Na⁺‐battery consists of a 154‐μm thick Na‐β′′‐Al₂O₃ electrolyte membrane, a 22‐μm thick P₂‐Na_2/3[Fe_1/2Mn_1/2]O₂ cathode and 52‐μm thick Na₂Ti₃O₇‐La_0.8Sr_0.2MnO₃ composite anode. The battery is shown to be capable of producing a reversible and stable capacity of 152 mAhg^?1 at 350 °C. While the battery's achievable capacity is limited by the electrode materials employed, it does exhibit unique low self‐discharge rate, high tolerance to thermal cycling and an outstanding safety feature.     

Free-Standing PEDOT-PSS/Ca<Subscript>3</Subscript>Co<Subscript>4</Subscript>O<Subscript>9</Subscript> Composite Films as Novel Thermoelectric Materials

Free-standing poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT- PSS)/Ca₃Co₄O₉ composite films have been successfully prepared by mechanically blending Ca₃Co₄O₉ powder and PEDOT-PSS solution (Baytron P) and casting the mixed solution on polypropylene (PP) film substrates. X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization indicated that the Ca₃Co₄O₉ particles were in the shape of sheets and composited well together with PEDOT-PSS. Thermoelectric (TE) measurements revealed that the Seebeck coefficient can be improved by increasing the Ca₃Co₄O₉ content in the composite films, with the largest enhancement being 24.8% compared with a free-standing PEDOT-PSS film. However, it is also shown that the power factor of the composite films decreases with increasing Ca₃Co₄O₉ content, mainly due to the decline of electrical conductivity and the limited improvement of the Seebeck coefficient.     

The Formation of Performance Enhancing Pseudo‐Composites in the Highly Active La1–xCaxFe0.8Ni0.2O3 System for IT‐SOFC Application

The La_1–xCa_xFe_0.8Ni_0.2O_3–δ (0 ≤ x ≤ 0.9) system is investigated for potential application as a cathode material for intermediate temperature solid oxide fuel cells (IT‐SOFCs). A broad range of experimental techniques have been utilized in order to elucidate the characteristics of the entire compositional range. Low A‐site Ca content compositions (x ≤ 0.4) feature a single perovskite solid solution. Compositions with 40% Ca content (x = 0.4) exhibit the highest electrical and ionic conductivities of these single phase materials (250 and 1.9 × 10^?3 S cm^?1 at 800 °C, respectively), a level competitive with state‐of‐the‐art (La,Sr)(Fe,Co)O₃. Between 40 and 50% Ca content (0.4 > x > 0.5) a solubility limit is reached and a secondary, brownmillerite‐type phase appears for all higher Ca content compositions (0.5 ≤ x ≤ 0.9). While typically seen as detrimental to electrochemical performance in cathode materials, this phase brings with it ionic conductivity at operational temperatures. This gives rise to the effective formation of pseudo‐composite materials which feature significantly enhanced performance characteristics, while also providing the closest match in thermal expansion behavior to typical electrolyte materials. This all comes with the advantage of being produced through a simple, single‐step, low‐cost production route without the issues associated with typical composite materials. The highest performing pseudo‐composite material (x = 0.5) exhibits electronic conductivity of 300–350 S cm^?1 in the 600–800 °C temperature range while the best polarisation resistance (R_p) values of approximately 0.2 Ω cm² are found in the 0.5 ≤ x ≤ 0.7 range.     

Unusual Strain Accommodation and Conductivity Enhancement by Structure Modulation Variations in Sr4Fe6O12+δ Epitaxial Films

Mixed ionic and electronic conducting (MIEC) films can be applied in solid state electrochemical devices such as oxygen separation membranes for producing pure oxygen, gas sensors or as cathode in solid oxide fuel cells. The current interest in layered perovskite‐related phases, like Sr₄Fe₆O₁₃ (SFO), arises from their significant oxygen permeability as predicted from theoretical studies. Nevertheless, before any practical application further fundamental study on this fairly unknown oxide is required mainly to assess the mechanisms affecting the transport properties. Epitaxial Sr₄Fe₆O_12+δ (SFO) films of b‐axis orientation with different thicknesses have been prepared by the pulsed laser deposition technique onto different perovskite substrates: SrTiO₃, NdGaO₃ and LaAlO₃. The strain accommodation has been found to vary as a function of film thickness as well as the substrate material causing different type of defects in the film microstructure, as well as variations in the oxygen anion content and ordering. Correspondingly, the total electrical conductivity of the films has been also found to vary significantly as a function of thickness and substrate type showing an unexpected enhancement for strained thin films. The variations in the transport properties are discussed in terms of the different strain accommodation mechanisms and the variation of the modulated structure observed for this compound.     

Solid‐State Photovoltaic Thin Films using TiO2, Organic Dyes,and Layer‐by‐Layer Polyelectrolyte Nanocomposites

We report photovoltaic devices consisting of patterned TiO₂, porphyrin dyes, and layer‐by‐layer (LBL) polyelectrolyte multilayer/oligoethylene glycol dicarboxylic acid (OEGDA) composite films. A composite polyelectrolyte LBL/OEGDA film was fabricated by formation of an alternating multilayer of linear polyethyleneimine (LPEI) and polyacrylic acid (PAA), followed by immersion of the LBL film into an OEGDA aqueous solution. The ionic conductivity attained in this LBL LPEI/PAA and OEGDA composite film was approximately 10^–5 S cm^–1 at room temperature and humidity. Investigations of dye‐sensitized photovoltaic devices constructed with the LBL (LPEI/PAA)/OEGDA composite films, TiO₂, and four types of porphyrin dyes resulted in optimization of the dye molecule and its orientation at the interface with the ionically conductive composite. The photocurrent value of photovoltaic devices constructed with the composite LBL/OEGDA film from illumination of a xenon white light source exhibited a nearly 1.5 times enhancement over the device without OEGDA. This enhancement of the photocurrent was due to the high room‐temperature ionic conductivity of the multilayer composite film. Further marked improvements of the photovoltaic performance were achieved by patterning the TiO₂ electrode using polymer stamping as a template for TiO₂ deposition. The device with patterned TiO₂ electrodes exhibited almost 10 times larger conversion efficiencies than a similar device without patterning.     

The optical properties of monolayer amorphous Al2O3–TiO2 composite films used as HT-APSM blanks for ArF immersion lithography

Amorphous (Al₂O₃)_x–(TiO₂)_1−x composite films are prepared using r.f. unbalanced magnetron sputtering in an atmosphere of argon and oxygen at room temperature. The optical constants of (Al₂O₃)_x–(TiO₂)_1−x composite films are linearly dependent on the Al₂O₃ mole fraction in the Al₂O₃–TiO₂ composite film. The optical constants of these Al₂O₃–TiO₂ composite films can be made to meet the optical requirements for a high transmittance attenuated phase shift mask (HT-APSM) blank by tuning the Al₂O₃ mole fraction. The Al₂O₃ mole fraction range that would allow the films to meet the optical requirements of an HT-APSM blank for ArF immersion lithography is calculated to be between 76% and 84%. One π-phase-shifted Al₂O₃–TiO₂ composite thin film to be used as an HT-APSM blank for ArF immersion lithography is fabricated and is shown to satisfy the optical requirements.     

Precise Tuning of (YBa2Cu3O7‐δ)1‐x:(BaZrO3)x Thin Film Nanocomposite Structures

Self‐assembled nanocomposite films and coatings have huge potential for many functional and structural applications. However, control and manipulation of the nanostructures is still at very early stage. Here, guidelines are established for manipulating the types of composite structures that can be achieved. In order to do this, a well studied (YBa₂Cu₃O_7‐δ)_1‐x:(BaZrO₃)_x ‘model’ system is used. A switch from BaZrO₃ nanorods in YBa₂Cu₃O_7‐δ matrix to planar, horizontal layered plates is found with increasing x, with a transitional cross‐ply structure forming between these states at x = 0.4. The switch is related to a release in strain energy which builds up in the YBa₂Cu₃O_7‐δ with increasing x. At x = 0.5, an unusually low strain state is observed in the planar composite structure, which is postulated to arise from a pseudo‐spinodal mechanism.     

Highly Conductive Porous Graphene/Ceramic Composites for Heat Transfer and Thermal Energy Storage

A novel architecture of 3D graphene growth on porous Al₂O₃ ceramics is proposed for thermal management using ambient pressure chemical vapor deposition. The formation mechanism of graphene is attributed to the carbothermic reduction occurring at the Al₂O₃ surface to initialize the nucleation and growth of graphene. The graphene films are coated on insulating anodic aluminum oxide (AAO) templates and porous Al₂O₃ ceramic substrates. The graphene coated AAO possesses one‐dimensional isolated graphene tubes, which can act as the media for directional thermal transport. The graphene/Al₂O₃ composite (G‐Al₂O₃) contains an interconnected macroporous graphene framework with an extremely low sheet electrical resistance down to 0.11 Ω sq^?1 and thermal conductivity with 8.28 W m^?1 K^?1. The G‐Al₂O₃ provides enormous conductive pathways for electronic and heat transfer, suitable for application as heat sinks. Such a porous composite is also attractive as a highly thermally conductive reservoir to hold phase change materials (stearic acid) for thermal energy storage. This work displays the great potential of CVD direct growth of graphene on dielectric porous substrates for thermal conduction and electronic applications.     

Pristine Titanium Carbide MXene Films with Environmentally Stable Conductivity and Superior Mechanical Strength

2D titanium carbide (Ti₃C₂T_x MXene) has potential application in flexible/transparent conductors because of its metallic conductivity and solution processability. However, solution‐processed Ti₃C₂T_x films suffer from poor hydration stability and mechanical performance that stem from the presence of intercalants, which are unavoidably introduced during the preparation of Ti₃C₂T_x suspension. A proton acid colloidal processing approach is developed to remove the extrinsic intercalants in Ti₃C₂T_x film materials, producing pristine Ti₃C₂T_x films with significantly enhanced conductivity, mechanical strength, and environmental stability. Typically, pristine Ti₃C₂T_x films show more than twofold higher conductivity (10 400 S cm^?1 vs 4620 S cm^?1) and up to 11‐ and 32‐times higher strength and strain energy at failure (112 MPa, 1,480 kJ m^?3, vs 10 MPa, 45 kJ m^?3) than films prepared without proton acid processing. Simultaneously, the conductivity and mechanical integrity of pristine films are also largely retained during the long‐term storage in H₂O/O₂ environment. The improvement in mechanical performance and conductivity is originated from the intrinsic strong interaction between Ti₃C₂T_x layers, and the absence of extrinsic intercalants makes pristine Ti₃C₂T_x films stable in humidity by blocking the intercalation of H₂O/O₂. This method makes the material more competitive for real‐world applications such as electromagnetic interference shielding.     

A Lyotropic Liquid‐Crystal‐Based Assembly Avenue toward Highly Oriented Vanadium Pentoxide/Graphene Films for Flexible Energy Storage

A novel lyotropic liquid‐crystal (LC) based assembly strategy is developed for the first time, to fabricate composite films of vanadium pentoxide (V₂O₅) nanobelts and graphene oxide (GO) sheets, with highly oriented layered structures. It is found that similar lamellar LC phases can be simply established by V₂O₅ nanobelts alone or by a mixture of V₂O₅ nanobelts and GO nanosheets in their aqueous dispersions. More importantly, the LC phases can be retained with any proportion of V₂O₅ nanobelts and GO, which allows facile optimization of the ratio of each component in the resulting films. Named VrGO, composite films manifest high electrical conductivity, good mechanical stability, and excellent flexibility, which allow them to be utilized as high performance electrodes in flexible energy storage devices. As demonstrated in this work, the VrGO films containing 67 wt% V₂O₅ exhibit excellent capacitance of 166 F g^?1 at 10 A g^?1; superior to those of the previously reported composites of V₂O₅ and nanocarbon. Moreover, the VrGO film in flexible lithium ion batteries delivers a high capacity of 215 mAh g^?1 at 0.1 A g^?1; comparable to the best V₂O₅ based cathode materials.     

Single crystal growth and solidification processing of RE123 superconductive oxides

Single crystal growth and bulk solidification processing in air are reviewed for the RE_1+xBa_2−xCu₃O_6+d solid solutions (RE123; RE=Sm, Nd). By changing the solvent and/or the initial composition from the usual composition of RE123—Sm₂Ba₁Cu₁O₅ (Sm211)/Nd₄Ba₂Cu₂O₁₀ (Nd422) to the Ba enriched side, RE123 crystals with a small amount of substitution were produced, which resulted in high T_c values of about 94–96 K for both single crystals and bulk materials. Another unique and interesting finding for the bulk processing includes the reduction of the RE211 particle size with increasing the BaO/CuO ratio in the initial composition. Uniform dispersion of the fine RE211 particles was attained in the RE123 matrix, which led to improve J_c values in relatively low magnetic fields of about 1 T. Changing the initial compositions toward the Ba enriched side is a simple and fundamental process for obtaining the bulk RE123 superconductor with high T_c and J_c values even in air, which in turn is an important and useful approach from the industrial point of view.     

Li6ALa2Ta2O12 (A = Sr, Ba): Novel Garnet‐Like Oxides for Fast Lithium Ion Conduction

Oxides with the nominal chemical formula Li₆ALa₂Ta₂O₁₂ (A = Sr, Ba) have been prepared via a solid‐state reaction in air using high purity La₂O₃, LiOH·H₂O, Sr(NO₃)₂, Ba(NO₃)₂, and Ta₂O₅ and are characterized by powder X‐ray diffraction (XRD) in order to identify the phase formation and AC impedance to determine the lithium ion conductivity. The powder XRD data of Li₆ALa₂Ta₂O₁₂ show that they are isostructural with the parent garnet‐like compound Li₅La₃Ta₂O₁₂. The cubic lattice parameter was found to increase with increasing ionic size of the alkaline earth ions (Li₆SrLa₂Ta₂O₁₂: 12.808(2) Å; Li₆BaLa₂Ta₂O₁₂: 12.946(3) Å). AC impedance results show that both the strontium and barium members exhibit mainly a bulk contribution with a rather small grain‐boundary contribution. The ionic conductivity increases with increasing ionic radius of the alkaline earth elements. The barium compound, Li₆BaLa₂Ta₂O₁₂, shows the highest ionic conductivity, 4.0×10^–5 S cm^–1 at 22 °C with an activation energy of 0.40 eV, which is comparable to other lithium ion conductors, especially with the presently employed solid electrolyte lithium phosphorus oxynitride (Lipon) for all‐solid‐state lithium ion batteries. DC electrical measurements using lithium‐ion‐blocking and reversible electrodes revealed that the electronic conductivity is very small, and a high electrochemical stability (&#62; 6 V/Li) was exhibited at room temperature. Interestingly, Li₆ALa₂Ta₂O₁₂ was found to be chemically stable with molten metallic lithium.     

Co3O4/Fe2O3异质结复合材料的制备及其紫外光光电探测性能

分别采用旋涂法和水热法在FTO衬底上制备Co₃O₄种子层和Co₃O₄薄膜,再在Co₃O₄薄膜上水热生长Fe₂O₃纳米棒,获得了高质量的Co₃O₄/Fe₂O₃异质结复合材料。通过改变Fe₂O₃前驱体溶液浓度来改变异质结复合材料中Fe₂O₃组分的含量。结果表明,Fe₂O₃纳米棒覆盖在呈网状结构的Co₃O₄薄膜上,随着Fe₂O₃前驱体溶液浓度即Fe₂O₃组分含量的增加,Co₃O₄/Fe₂O₃异质结复合材料对紫外光的响应逐渐增强,当Fe₂O₃前驱体溶液浓度为0.015mol/L时,异质结复合材料有着很好的光电稳定性,并表现出较高的响应率(12.5mA/W)和探测率(4.4×10¹⁰Jones)。     

Anomalous Oxidation States in Multilayers for Fuel Cell Applications

Significant recent interest has been directed towards the relationship between interfaces and reports of enhanced ionic conductivity. To gain a greater understanding of the effects of hetero‐interfaces on ionic conductivity, advanced analytical techniques including electron microscopy (TEM/STEM), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are used to characterize CeO₂/Ce_0.85Sm_0.15O₂ multilayer thin films grown by pulsed laser deposition. High quality growth is observed, but ionic conductivity measured by impedance spectroscopy and ¹⁸O tracer experiments is consistent with bulk materials. EELS analysis reveals the unusual situation of layers containing only Ce(IV) adjacent to layers containing both Ce(III) and Ce(IV). Post oxygen annealing induced oxygen diffusion and mixed oxidation states in both layers, but only in the vicinity of low angle grain boundaries perpendicular to the layers. The implications of the anomalous behavior of the Ce oxidation states on the design of novel electrolytes for solid oxide fuel cells is discussed.     

Synthesis and Characterization of Magnesium-Alloyed Hematite Thin Films

We have synthesized pure and Mg-alloyed hematite thin films on F-doped, SnO₂-coated glass substrates by radiofrequency magnetron cosputtering of iron oxide with and without MgO sources in mixed Ar/O₂ and mixed N₂/O₂ ambient. We found that hematite films deposited in N₂/O₂ ambient exhibited much poorer crystallinity than those deposited in Ar/O₂ ambient. We determined that Mg alloying led to increased crystallinity and bandgap. Furthermore, we found that Mg alloying inverted the type of conductivity of the thin films: pure hematite thin films exhibited n-type conductivity, whereas Mg-alloyed hematite thin films exhibited p-type conductivity.