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In recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X‐ray photoelectron spectroscopy (XPS) and in‐situ Raman spectroscopy to investigate the oxidation properties of yttria‐stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO2), gadolinium‐doped ceria (GDC) and zirconia‐doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce3+ to Ce4+, while gadolinium doping results in a decrease of Ce3+. The presence of Ni increases the Ce3+/Ce4+ ratio for CeO2 and GDC, but had little effect on ZDC. We used the shift of the F2g Raman peak to monitor in‐situ, the oxidation state of ceria. In the as‐made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 °C when co‐infiltrated with Ni. In‐situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.

Strontium molybdate (SrMoO3) thin films are grown epitaxially on strontium titanate (SrTiO3), magnesium oxide (MgO), and lanthanum aluminate (LaAlO3) substrates by pulsed laser deposition and possess electrical resistivity as low as 100 µΩ cm at room temperature. SrMoO3 is shown to have optical losses, characterized by the product of the Drude broadening, ΓD, and the square of the plasma frequency, ωpu2, significantly lower than TiN, though generally higher than Au. Also, it is demonstrated that there is a zero-crossover wavelength of the real part of the dielectric permittivity, which is between 600 and 950 nm (2.05 and 1.31 eV), as measured by spectroscopic ellipsometry. Moreover, the epsilon near zero (ENZ) wavelength can be controlled by engineering the residual strain in the films, which arises from a strain dependence of the charge carrier concentration, as confirmed by density of states calculations. The relatively broad tunability of ENZ behavior observed in SrMoO3 demonstrates its potential suitability for transformation optics along with plasmonic applications in the visible to near infrared spectral range.

Raman spectroscopy is a powerful characterization tool for improving the understanding of solid oxide fuel cells (SOFCs), capable of providing direct, molecularly specific information regarding the physical and chemical processes occurring within functional SOFCs in real time. In this paper we give a summary of the technique itself and highlight ex situ and in situ studies that are particularly relevant for SOFCs. This is followed by a case study of carbon formation on SOFC Ni-based anodes exposed to carbon monoxide (CO) using both ex situ and in situ Raman spectroscopy combined with computational simulations. In situ measurements clearly show that carbon formation is significantly reduced for polarized SOFCs compared to those held at open circuit potential (OCP). Ex situ Raman mapping of the surfaces showed clear variations in the rate of carbon formation across the surface of polarized anodes. Computational simulations describing the geometry of the cell showed that this is due to variations in gas access. These results demonstrate the ability of Raman spectroscopy in combination with traditional characterization tools, to provide detailed understanding of critical processes occurring within functional SOFCs.

Direct metal laser sintering is used to create 3D hierarchical porous metallic scaffolds which are then functionalized with a co‐electrodeposition of MnO2, Mn2O3, and doped conducting polymer. This approach of functionalizing metal 3D printed scaffolds thus opens new possibilities for structural energy storage devices with enhanced performance and lifetime characteristics.

The magnetocaloric effect has seen a resurgence in interest over the last 20 years as a means towards an alternative energy efficient cooling method. This has resulted in a concerted effort to develop the so-called “giant” magnetocaloric materials with large entropy changes that often come at the expense of hysteretic behavior. But do the gains offset the disadvantages? In this paper, we review the relationship between the latent heat of several giant magnetocaloric systems and the associated magnetic field hysteresis. We quantify this relationship by the parameter Δμ 0 H/ΔS L, which describes the linear relationship between field hysteresis, Δμ 0 H, and entropy change due to latent heat, ΔS L. The general trends observed in these systems suggest that itinerant magnets appear to consistently show large ΔS L accompanied by small Δμ 0 H (Δμ 0 H/ΔS L = 0.02 ± 0.01 T/(J K−1 kg−1)), compared to local moment systems, which show significantly larger Δμ 0 H as ΔS L increases (Δμ 0 H/ΔS L = 0.14 ± 0.06 T/(J K−1 kg−1)).

An effective, low-temperature and readily available electrochemical method for tuning the operation temperature of LaFe(13-x)Si(x)-type alloys is demonstrated. Electrolytically hydrided materials have the same high level magnetic properties as in high temperature gas-phase processed materials and offer an advantage of higher hydrogen absorption rate in the ferromagnetic state.

FeSe1−x samples have been prepared by a solid-state reaction in the Ar+3% H2 gas flow. The samples sintered at 410°C were of the tetragonal PbO structure (β-phase), showing little trace of δ-phase (hexagonal). However, the samples sintered at higher temperatures contained a fair amount of δ-phase, which was unable to be eliminated completely by subsequent annealing at ≤450°C for a prolonged period. Both M–T and R–T measurements showed that sintered samples of β-phase were superconducting with an onset Tc above 8.1 K. Thick films of FeSe1−x were grown on LaAlO3 substrates by liquid phase processing with SeSn as the flux. In contrast to the sintering, the films grown around 910°C from the Sn-containing liquid had a pure β-phase. Although the phase diagram showed some solid solubility of Sn in FeSe, energy-dispersive X-ray spectroscopy failed to find Sn trace in the crystallized films, which showed a steeper superconducting transition at lower Tc of 6.0 K. To clarify whether the possible Sn contamination caused the drop of Tc, FeSe1−x:5% Sn samples were sintered, which showed little change of Tc from the pure β-FeSe1−x. The cause for the Tc reduction of thick films remains unclear.

The authors thank EPSRC for support through the research grant EP/M014304/1. The key technical challenges that fuel cell developers need to address are performance, durability, and cost. All three need to be achieved in parallel; however, there are often competitive tensions, e.g., performance is achieved at the expense of durability. Stability and resistance to degradation under prolonged operation are key parameters. There is considerable interest in developing new cathodes that are better able to function at lower temperature to facilitate low cost manufacture. For anodes, the ability of the solid oxide fuel cell (SOFC) to better utilize commonly available fuels at high efficiency, avoid coking and sulfur poisoning or resistance to oxidation at high utilization are all key. Optimizing a new electrode material requires considerable process development. The use of solution techniques to impregnate an already optimized electrode skeleton, offers a fast and efficient way to evaluate new electrode materials. It can also offer low cost routes to manufacture novel structures and to fine tune already known structures. Here impregnation methodologies are discussed, spectral and surface characterization are considered, and the recent efforts to optimize both cathode and anode functionalities are reviewed. Finally recent exemplifications are reviewed and future challenges and opportunities for the impregnation approach in SOFCs are explored. Postprint

Metamagnets are materials with first-order phase transition from one magnetically ordered phase to another that could provide environmentally friendly, highly efficient refrigeration near ambient temperatures using a phenomenon known as the magnetocaloric effect. Profoundly important to fundamental research and the application of room-temperature magnetic refrigeration (a solid-state cooling method that takes advantage of the entropy change associated with changes in magnetic order), is the need to understand how the metamagnetic transition evolves, and whether it can be manipulated by nanoengineering, or chemical substitutions to be sharper, occur at a lower magnetic driving fields, or be less hysteretic. Here, using Hall probe imaging, we show that inclusions of mesocopic platelets of Gd5Si1.5Ge1.5, that are inherent to all single crystals and polycrystals of this compound, seed the global metamagnetic transition to the ferromagnetic state across the Gd5Si2Ge2 crystal. We show that these inclusions, as well as well-defined mosaic boundaries, play a dramatic role on the transition properties. Strain and the associated field-driven volume changes underpin the phenomena that we have observed, and show that nanostructuring is the likely route to a more complete control of the critical properties in these materials. Themagnetic cooling field has a historic past, first conceived in the 1920’s by P. Debye and W. Giauque; the concepts have been used to reach extremely low temperatures in a process known as adiabatic demagnetization. Over the past ten years, the field has experienced a resurgence of interest after the discovery of giant magnetocaloric effects in a family of materials known as metamagnets, which are compounds that undergo a first-order transition to a magnetically ordered state, often accompanied by a coincident transformation of the crystal structure. Gd5Si2Ge2 has attracted a great deal of interest in this important area because it could play a pivotal role for energy-efficient magnetic cooling near room temperatures. It is a paramagnet (PM) above 274K with a monoclinic crystal structure; by applying a magnetic field, the material can be converted to a ferromagnetic (FM) state with a different, yet closely related, orthorhombic structure via a first-order transition. It has been shown that alloying Gd5Si2Ge2 with different elements substituting for either Si and Ge, or Gd can tune the critical temperature,Tc, but this leads to a significant shift in the magnetic character from first-order towards second-order behavior, which has an adverse effect on the magnitude of the magnetocaloric effect. Although these are interesting facts, it is true to say that a proper fundamental understanding of how to engineer the metamagnetic transition to optimize the magnetocaloric effect has yet to be established. Conventional structural characterization techniques, such as scanning and transmission electron microscopies (SEM, TEM), and X-ray diffraction have proved to be vitally important for understanding of the Gd5Si2Ge2 compound. High-resolution TEM has shown that all the Gd5Si2Ge2 crystals have a complex microstructure consisting of a dominant matrix of the singlephase parent material that is interspersed with extremely thin-plates (200 nm thick) of a second phase Gd5(SixGe1–x)3 material. In this sense the crystals are not pure, but single-crystal-like diffraction patterns are observed by backscatter Laue technique, and so for all intents and purposes these samples can indeed be considered single crystals. The platelets arrange themselves in a criss-cross pattern when viewed perpendicular or nearly perpendicular to the [010] face (see Fig. 1), with platelets extending for several hundred micrometers. When viewed perpendicular to both the [100] and [001] faces, the platelets

Co-doped TiO 2 films were characterized by spectroscopic ellipsometry to determine their thickness, deposition rate and optical properties as function of substrate temperature and background gas composition. To fit the data we used a combination of a single Tauc-Lorentz oscillator with the Drude free electron model to take in account the free electrons present in the film. The Co doping and the addition of H 2 to the gas phase during film growth cause the formation of a titanium oxide which containsfree electrons that absorb the energy of the red part of the spectrum, causing k to increase The n of the films at 1.5 eV is about 2.3 eV. The fittigs also show that the n of films decreases and k increases at the surface. This can be related to a segregation of Co to the surface which in some cases, of high substrate temperature and high H 2 flow during deposition, can lead to an even higher concentration of free electrons at the surface.

In this work we report on the structure and magnetic and electrical transport properties of CrO2 films deposited onto (0001) sapphire by atmospheric pressure (AP)CVD from a CrO3 precursor. Films are grown within a broad range of deposition temperatures, from 320 to 410 °C, and oxygen carrier gas flow rates of 50–500 sccm, showing that it is viable to grow highly oriented a-axis CrO2 films at temperatures as low as 330 °C i.e., 60–70 °C lower than is reported in published data for the same chemical system. Depending on the experimental conditions, growth kinetic regimes dominated either by surface reaction or by mass-transport mechanisms are identified. The growth of a Cr2O3 interfacial layer as an intrinsic feature of the deposition process is studied and discussed. Films synthesized at 330 °C keep the same high quality magnetic and transport properties as those deposited at higher temperatures.

Oxygen cycling of Sr2Fe2-xMoxO6-delta (SFMO) samples allows the resistivity and low-field magnetoresistance (LFMR) to be precisely cycled. TEM shows that the change in resistivity with oxygen is not only a consequence of the change in oxygen stoichiometry of SFMO, but also a concomitant change in the Fe/Mo ratio in SFMO. The figure shows the change in MR and resistivity (values in m Omega cm above the data points for samples D1-D7) with increasing post-annealing time

A scanning micro-Raman study of mechanically bevelled GaSb/InAs single quantum-well samples was carried out with 488- and 514-nm laser excitation wavelengths. The bevelling process magnifies the vertical resolution of interfaces and the quantum-well region. We demonstrate that the depth profile of the first-order Raman modes can be used to characterise individual layers with high spatial resolution of nanometer order. The red shift of the InAs longitudinal optical modes in the quantum well relative to that of bulk InAs provides clear evidence of compressive strain in the quantum well region. A method to estimate the quantum well thickness is also demonstrated.

Hysteresis is detrimental to the refrigeration cooling cycle efficiency and yet many of the magnetocaloric materials under consideration as solid state refrigerants possess this property. This article discusses some aspects related to the factors leading to hysteresis in real materials. In the absence of high quality single crystals, determining the intrinsic energy cost associated with the transformation between metastable phases is an experimental challenge. We describe a micro‐calorimetric method that provides valuable insight into intrinsic behavior with the sensitivity to measure micro‐crystallites. We show that there is no correlation between the strength of first order character and magnitude of hysteresis between material families. We review some of the extrinsic factors which contribute to the hysteresis in real materials particularly those that can be accounted for using local imaging techniques such as scanning Hall probe microscopy. We discuss a number of mechanisms by which the extrinsic hysteretic properties of a material can be modified.

We study the magnetocaloric metamagnetic transition in LaFe11.74Mn0.06Si1.20 and LaFe11.76Mn0.06Si1.18H1.65 under hydrostatic pressure up to 1.2 GPa. For both compounds, hydrostatic pressure depresses the zero field critical temperature. However, in detail, pressure influences the magnetic properties in different ways in the two compounds. In the dehydrogenated case the transition broadens under pressure whereas in the hydrogenated case the transition sharpens. In both cases thermal hysteresis increases under pressure, although with different trends. These observations suggest both intrinsic and extrinsic hysteresis loss brought about by the use of hydrostatic pressure. We explore the multicaloric field-pressure cycle, demonstrating that although the gain introduced by overcoming the magnetic hysteresis loss is closely countered by the loss introduced in the pressure cycle, there are significant advantages in that the temperature range of operation can be finely tuned and extended, and the magnetocaloric transition can operate in lower absolute applied fields (

Annealing studies were conducted on bulk La0.7Ca0.3MnO3−δ to determine the sensitivity of its structural and magnetic properties to oxygenation conditions. Standard bulk sintering conditions, thin-film annealing conditions for obtaining good magnetoresistive properties, and a reducing anneal, which corresponded to the onset of phase decomposition, were conducted. The main phase formed was a face-centered (fcc) pseudocubic double-perovskite structure, with cell parameters of a∼ 2ap∼ 0.772 nm, where ap is the single-perovskite cubic cell parameter. A minor superstructure—body-centered pseudotetragonal, with lattice parameters of c= 4ap and a=√2ap—was observed in samples with (3 −δ) < 3. A maximum of 20% of the superstructure was formed using the most-reducing conditions. The superstructure had a lower critical temperature than the main phase and depressed ferromagnetic order.

The dielectric loss (tan δ) of titanium dioxide (TiO2) disks has been measured at a frequency of 3 GHz. High-purity TiO2 sintered to almost-full density exhibits a very high tan δ, which is interpreted to be due to oxygen deficiency. To counter this, doping with stable divalent and trivalent cations, such as Mg and Al, leads to a low tan δ, probably by preventing Ti4+ reduction. The tan δ of polycrystalline TiO2 doped with divalent and trivalent ions with ionic radii in the range of 0.5–0.95 A at 3 GHz can be very low: 6 × 10−5 (Q∼ 17 000) at a temperature of 300 K. The tan δ of undoped pure TiO2 disks increases when the disks are cooled from 300 K to ∼100 K. At temperatures

We report on the synthesis of highly oriented a-axis CrO2 films onto (0001) sapphire by atmospheric pressure CVD from CrO3 precursor, at growth temperatures down to 330 degree Celsius, i.e. close to 70 degrees lower than in published data for the same chemical system. The films keep the high quality magnetic behaviour as those deposited at higher temperature, which can be looked as a promising result in view of their use with thermally sensitive materials, e.g. narrow band gap semiconductors., 13 pages, 4 figures

Hysteresis is unattractive for magnetocaloric applications because it introduces loss in the cooling cycle. It is however usually associated with a first order transition and large entropy change. In this paper we review the sources of hysteresis in magnetocaloric materials and in particular in manganite systems where the nature of the transition in terms of whether it is indeed a first order transition remains elusive.

Magnesium diboride, MgB2, has a relatively high superconducting transition temperature1, placing it between the families of low- and high-temperature (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhindered by grain boundaries2,3, making it potentially attractive for technological applications in the temperature range 20–30 K. But in the bulk material, the critical current density (Jc) drops rapidly with increasing magnetic field strength4. The magnitude and field dependence of the critical current are related to the presence of structural defects that can ‘pin’ the quantized magnetic vortices that permeate the material, and a lack of natural defects in MgB2 may be responsible for the rapid decline of Jc with increasing field strength3. Here we show that modest levels of atomic disorder induced by proton irradiation enhance the pinning of vortices, thereby significantly increasing Jc at high field strengths. We anticipate that either chemical doping or mechanical processing should generate similar levels of disorder, and so achieve performance that is technologically attractive in an economically viable way.

In this tutorial review, the underlying principles of vibrational pumping in surface enhanced Raman scattering (SERS) are summarized and explained within the framework of their historical development. Some state-of-the-art results in the field are also presented, with the aim of giving an overview on what has been established at this stage, as well as hinting at areas where future developments might take place.