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We report on the structural, magnetic and magnetocaloric properties of the Ni50Mn38Sb12Bx alloys in term of boron addition with x = 1, 3 and 5. We have found that both the paramagnetic–ferromagnetic austenitic transition (TC) and the ferromagnetic–antiferromagnetic martensitic transition (TM) are sensitively influenced by the boron addition: TC tends to increase, while TM decreases with increasing boron concentration. Temperature dependent X-ray diffraction in the range of 200–500 K clearly shows an evolution of the structural transformation from orthorhombic to cubic structure phase transition on heating for the x = 1 and 3 samples. Strikingly, the addition of boron atoms into the lattice favours the ferromagnetic ordering relatively to the antiferromagnetic arrangement below TM. This consequently affects on the magneto-structural transition as well as on the size of magnetocaloric effect.

FeSb 2 films were produced in a low-pressure Ar environment by pulsed laser deposition at 355 nm. The influence of growth parameters such as substrate temperature, Ar pressure and deposition time on the growth of FeSb 2 films was studied. Nearly phase-pure FeSb 2 films with thicknesses of 100–400 nm were produced at 425 °C with an Ar pressure of 1.5–2 Pa. Thermal transport and Hall measurements were performed to explore the thermoelectric transport properties of the FeSb 2 films. A maximum thermopower of ∼120 μVK −1 at 40 K was obtained. In general it is highly important to understand the growth properties of FeSb 2 films if they are to eventually reach thermoelectric applications at cryogenic temperatures.

The homoepitaxial growth of SrTiO 3 (STO) films was investigated by a large-area pulsed laser deposition (PLD), which was in-situ monitored by a high pressure reflective high energy electron diffraction. By combining a conventionally continuous film deposition with a followed interval relaxation, a persistent layer-by-layer (LBL) film growth of more than 100 unit cells STO films was achieved. This interrupted PLD technique could realize persistent LBL film growth at any laser frequency between 1 and 10 Hz and provides an effective way to fabricate high quality complex oxide films on unit cell scale.

A general scheme for increasing the difference in magnetic flux density between a high and a low magnetic field region by removing unnecessary magnet material is presented. This is important in, e.g., magnetic refrigeration where magnet arrays has to deliver high field regions in close proximity to low field regions. Also, a general way to replace magnet material with a high permeability soft magnetic material where appropriate is discussed. As an example these schemes are applied to a two dimensional concentric Halbach cylinder design resulting in a reduction of the amount of magnet material used by 42% while increasing the difference in flux density between a high and a low field region by 45%., Comment: 7 pages, 8 figures

Ultrathin crystalline films of 10 mol% gadolinia-doped ceria (CGO10) are grown on MgO (100) substrates by pulsed laser deposition at a moderate temperature of 400°C. As-deposited CGO10 layers of approximately 4 nm, 14 nm, and 22 nm thickness consist of fine grains with dimensions ≤∼11 nm. The films show high density within the thickness probed in the X-ray reflectivity experiments. Thermally activated grain growth, density decrease, and film surface roughening, which may result in the formation of incoherent CGO10 islands by dewetting below a critical film thickness, are observed upon heat treatment at 400°C and 800°C. The effect of the grain coarsening on the electrical characteristics of the layers is investigated and discussed in the context of a variation of the number density of grain boundaries. The results are evaluated with regard to the use of ultrathin CGO10 films as seeding templates for the moderate temperature growth of thick solid electrolyte films with improved oxygen transport properties.

A La0.67Ca0.26Sr0.07Mn1.05O3 (LCSM) perovskite was prepared for the first time as a ceramic monolithic regenerator used in a regenerative magnetic refrigeration device. The parameters influencing the extrusion process and the performance of the regenerator, such as the nature of the monolith paste and the influence of the sintering on the adiabatic temperature change, were investigated. Comparisons between the extruded monolithic structure before and after the sintering showed that an increase of the adiabatic temperature change was seen after the sintering. Furthermore, calculations show that the performance of the monolithic structure is potentially superior to a parallel plate regenerator, indicating the potential cost and structural benefit of using such structure, i.e. a mechanically stable ceramic thin wall structure, which can be produced in one processing step.

The effects of Ga substitution on the Co-site on the high-temperature thermoelectric properties and microstructure are investigated for the misfitlayered Ca3Co4O9 and the complex perovskite-related Sr3RECo4O10.5 (RE = rare earth) cobalt-based oxides. For both systems, substitution of Ga for Co results in a simultaneous increase in the Seebeck coefficient (S) and the electrical conductivity (σ), and the influence is more significant in the high temperature region. The power factor (S 2 σ) is thereby remarkably improved by Ga substitution, particularly at high temperatures. Texture factor calculations using x-ray diffraction pattern data for pressed and powder samples reveal that the Ga-doped samples are highly textured. Microstructure observed by scanning electron microscopy shows very well-crystallized grains for the samples with Ga substitution for Co. Among the Ga-doped samples, Ca3Co3.95Ga0.05O9 shows the best ZT value of 0.45 at 1200 K, which is about 87.5% higher than the nondoped one, a considerable improvement.

Polycrystalline SnO2-based samples (Sn0.97−xSb0.03ZnxO2, x = 0, 0.01, 0.03) were prepared by solid-state reactions. The thermoelectric properties of SnO2 doped with Sb and Zn were investigated from 300 K to 1100 K. X-ray diffraction (XRD) analysis revealed all XRD peaks of all the samples as identical to the rutile structure, except for the x = 0.03 sample, which had a small amount of Zn2SbO4 as a secondary phase. We found that the power factor of the x = 0.03 sample was significantly improved due to the simultaneous increase in the electrical conductivity and the Seebeck coefficient. A power factor value of ∼2 × 10−4 W m−1 K−2 was obtained for the x = 0.03 sample at 1060 K, 126% higher than that for the undoped sample.

The conductance confined at the interface of complex oxide heterostructures provides new opportunities to explore nanoelectronic as well as nanoionic devices. Herein we show that metallic interfaces can be realized in SrTiO3-based heterostructures with various insulating overlayers of amorphous LaAlO3, SrTiO3 and yttria-stabilized zirconia films. On the other hand, samples of amorphous La7/8Sr1/8MnO3 films on SrTiO3 substrates remain insulating. The interfacial conductivity results from the formation of oxygen vacancies near the interface, suggesting that the redox reactions on the surface of SrTiO3 substrates play an important role., 17 pages, 4 figures

A magnet designed for use in a magnetic refrigeration device is presented. The magnet is designed by applying two general schemes for improving a magnet design to a concentric Halbach cylinder magnet design and dimensioning and segmenting this design in an optimum way followed by the construction of the actual magnet. The final design generates a peak value of 1.24 T, an average flux density of 0.9 T in a volume of 2 L using only 7.3 L of magnet, and has an average low flux density of 0.08 T also in a 2 L volume. The working point of all the permanent magnet blocks in the design is very close to the maximum energy density. The final design is characterized in terms of a performance parameter, and it is shown that it is one of the best performing magnet designs published for magnetic refrigeration., Comment: 6 pages, 6 figures

A two-dimensional finite element model describing the performance of parallel-plate regenerators with arbitrary channel width distributions has been developed in order to investigate the effect of non-uniform plate spacing on the performance of regenerators. Results for a series of hypothetical plate spacing distributions are presented in order to understand the impact of spacing non-uniformity. Simulations of more realistic distributions where the plate spacings follow normal distributions are then discussed in order to describe the deviation of the performance of a regenerator relative to one with uniform spacing as a function of the standard deviation of the plate distribution. It has been shown that the most significant reduction in performance occurs when a volume of fluid between 100% and 200% of the regenerator void volume is displaced in a single blow.

Electrical characterization of 10 mol% gadolinia doped ceria (CGO10) films of different thicknesses prepared on MgO(100) substrates by pulsed laser deposition is presented. Dense, polycrystalline and textured films characterized by fine grains (grain sizes < 18 nm and < 64 nm for a 20-nm and a 435-nm film, respectively) are obtained in the deposition process. Grain growth is observed under thermal cycling between 300 and 800°C, as indicated by X-ray-based grain-size analysis. However, the conductivity is insensitive to this microstructural evolution but is found to be dependent on the sample thickness. The conductivity of the nanocrystalline films is lower (7.0×10−4 S/cm for the 20-nm film and 3.6×10−3 S/cm for the 435-nm film, both at 500°C) than that of microcrystalline, bulk samples ( $6\times 10^{-3}$ S/cm at 500°C). The activation energy for the conduction is found to be 0.83 eV for the bulk material, while values of 1.06 and 0.80 eV are obtained for the 20-nm film and the 435-nm film, respectively. The study shows that the ionic conductivity prevails in a broad range of oxygen partial pressures, for example down to about 10 −26 atm at 500°C.

Nanocrystalline (nc) scandia-stabilized zirconia (SSZ) electrolytes with scandia contents of 5.9 to 15.9 mol% ere synthesized by reactive magnetron sputtering. For scandia content andgt;= 9.1 mol%, the as-deposited films were pure cubic phase with andlt; 111 andgt; texture, while traces of tetragonal phase was found for lower Sc content. Single-line profile analysis of the 111 X-ray diffraction peak yielded an out-of-plane grain size of similar to 10 nm and a microstrain of 2.0-2.2%, regardless of scandia content, for films deposited at 400 degrees C and a bias of -70 V. Films deposited at higher bias voltages showed a reduced grain size, yielding a grain size of similar to 6 nm and a microstrain of similar to 2.5% at -200 V and -250 V with additional incorporation of argon. Temperature-dependent impedance spectroscopy of the SSZ films showed that the in-plane ionic conductivity had a maximum close to 10.7 mol% and decreased almost an order of magnitude as the scandia - content was increased to 15.9 mol%. The activation energy for oxygen ion migration was determined to be between 130-1.43 eV. In addition, no dependence on grain size was observed. The above observations suggest a bulk mechanism for ionic conduction. Original Publication:M Sillassen, Per Eklund, N Pryds, N Bonanos and J Bottiger, Concentration-dependent ionic conductivity and thermal stability of magnetron-sputtered nanocrystalline scandia-stabilized zirconia, 2010, SOLID STATE IONICS, (181), 23-24, 1140-1145.http://dx.doi.org/10.1016/j.ssi.2010.06.010Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/

Thin films composed of alternating Al/Cu/Al layers were deposited on a (111) Si substrate using pulsed laser deposition (PLD). The thicknesses of the film and the individual layers, and the detailed internal structure within the layers were characterized by means of transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and energy-filtered TEM (EFTEM). Each Al or Cu layer consists of a single layer of nano-sized grains of different orientations. EFTEM results revealed a layer of oxide about 2 nm thick on the surface of the Si substrate, which is considered to be the reason for the formation of the first layer of nano-sized Al grains. The results demonstrate that the PLD technique is a powerful tool to produce nano-scale multilayered metal films with controllable thickness and grain sizes.

A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span and exergy. The results show that the optimal AMR should have a utilization in the range 0.2–1 and an NTU higher than 10 and not necessarily more than 30. It is concluded that parallel plate-based regenerators face significant challenges in terms of manufacturability. However, the benefit of parallel plate regenerators is a very low pressure drop, which is needed for high performance.

Four highly reduced molybdenum oxides LnMo 8 O 14 (Ln = La, Ce, Nd and Sm) containing bicapped Mo 8 clusters were synthesized via solid state reaction followed by spark plasma sintering. The thermoelectric properties were investigated, and NdMo 8 O 14 exhibits the best performance with the maximum power factor of 177 μW/mK 2 at 1000 K. The highest ZT of NdMo 8 O 14 was determined to be around 0.1 at 1000 K.

Very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia (YSZ) synthesized on single-crystal SrTiO3and MgO substrates by reactive direct current magnetron sputtering are reported. Superionic conductivities (i.e., ionic conductivities of the order similar to 1 Omega(-1)cm(-1)) are observed at 500 degrees C for 58-nm-thick films on MgO. The results indicate a superposition of two parallel contributions - one due to bulk conductivity and one attributable to conduction along the film substrate interface. Interfacial effects dominate the conductivity at low temperatures (andlt;350 degrees C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk-like conductivity is observed. The films have a negligible grain-boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150-500 degrees C are of great fundamental importance but may also be technologically relevant for low-temperature applications. Original Publication:Michael Sillassen, Per Eklund, Nini Pryds, Erik Johnson, Ulf Helmersson and Jorgen Bottiger, Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized Zirconia, 2010, ADVANCED FUNCTIONAL MATERIALS, (20), 13, 2071-2076.http://dx.doi.org/10.1002/adfm.201000071Copyright: John Wiley & Sons, Ltdhttp://eu.wiley.com/WileyCDA/Brand/id-35.html

Alloys displaying positive enthalpy of mixing demix below a critical temperature. In Co-Cu and related ternaries the miscibility gap is metastable, i.e. it occurs at temperatures lower than the liquidus. In order to study the liquid phase separation high melt undercooling is necessary. This was obtained via rapid solidification techniques using melt spinning and casting in moulding devices, as well as high temperature DSC experiments with samples embedded in a flux. Results are given for Co-Cu, Co-Cu-Fe and Co-Cu-Ni systems. Phase diagrams were optimised using the DSC data. The mechanism of phase separation was investigated by comparing samples produced under different cooling conditions. The hierarchy of microstructures obtained was interpreted accounting for the processing technique and the phase diagram. They constitute a database useful for the interpretation of the thermal history of samples processed in microgravity.

Electron microscopy characterization across the cathode-electrolyte interface of two different types of intermediate temperature solid oxide fuel cells (IT-SOFC) is performed to understand the origin of the cell performance disparity. One IT-SOFC cell had a sprayed-cosintered Ce(0.90)Gd(0.01)O(1.95) (CGO10) barrier layer, the other had a barrier layer deposited by pulsed laser deposition (PLD) CGO10. Scanning electron microscopy, transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD) investigations conclude that the major source of the cell performance difference is attributed to CGO-YSZ interdiffusion in the sprayed-cosintered barrier layer. From TEM and EBSD work, a dense CGO10 PLD layer is found to be deposited epitaxially on the 8YSZ electrolyte substrate-permitting a small amount of SrZrO(3) formation and minimizing CGO-YSZ interdiffusion.

The series LnMo 8 O 14 (Ln = La, Ce, Pr, Nd and Sm) containing bicapped Mo 8 clusters was synthesized via solid state reaction at 1673 K. Oxides of this type were reported to be narrow gap semiconductors. Our Seebeck coefficient measurements show that some of these reduced molybdenum oxides exhibit a thermopower of above −100 μV/K at room temperature, which is promising for the thermoelectric application. The highest power factor of 71 μW/mK 2 was obtained for SmMo 8 O 14 at 1152 K.

In order to establish a new platform to manufacture micro-sized solid oxide fuel cells (SOFCs) with low operating temperatures, new design concepts, new preparation methods and new materials are being explored. Our studies in this paper are focused on the electrolyte material, and in particular gadolinia doped ceria (GDC), an electrolyte material, likely to replace the traditional yttria-stabilised zirconia (YSZ) for low temperature applications. GDC films were grown on a single crystal Si by pulsed laser deposition (PLD). The microstructure of the films as a function of growth time has been studied. We have found that the mean grain size increases with film thickness h as h2/5, in agreement with theoretical results.

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the growth of thin films of titanium dioxide (TiO2) on (1 0 0) magnesium oxide (MgO) substrates by pulsed laser deposition (PLD). The deposition is performed with a synthetic rutile TiO2 target at low fluence. The topography and structure of the deposited layers are characterized using in situ high pressure RHEED and atomic force microscope (AFM). Based on these observations the growth mode of the films is discussed. The results will be compared to earlier results obtained for the growth of TiN films on (1 0 0) MgO.

Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the initial growth of titanium nitride (TiN) thin films on single-crystal (100) MgO substrates by pulsed laser deposition (PLD). This is the first RHEED study where the growth of TiN films is produced by PLD directly from a TiN target. At the initial stage of the growth (average thickness ∼2.4 nm) the formation of islands is observed. During the continuous growth the islands merge into a smooth surface as indicated by the RHEED, atomic force microscopy and field emission scanning electron microscopy. These observations are in good agreement with the three-dimensional Volmer–Weber growth type, by which three-dimensional crystallites are formed and later cause a continuous surface roughening. This leads to an exponential decrease in the intensity of the specular spot in the RHEED pattern as well.

A time-dependent, two-dimensional mathematical model of a reciprocating Active Magnetic Regenerator (AMR) operating at room-temperature has been developed. The model geometry comprises a regenerator made of parallel plates separated by channels of a heat transfer fluid and a hot as well as a cold heat exchanger. The model simulates the different steps of the AMR refrigeration cycle and evaluates the performance in terms of refrigeration capacity and temperature span between the two heat exchangers. The model was used to perform an analysis of an AMR with a regenerator made of gadolinium and water as the heat transfer fluid. The results show that the AMR is able to obtain a no-load temperature span of 10.9 K in a 1 T magnetic field with a corresponding work input of 93.0 kJ m−3 of gadolinium per cycle. The model shows significant temperature differences between the regenerator and the heat transfer fluid during the AMR cycle. This indicates that it is necessary to use two-dimensional models when a parallel-plate regenerator geometry is used.

Single layer dense films of La 0.8 Sr 0.2 Cr 0.97 V 0.03 O 3 (LSC) and MnCr 2 O 4 with a thickness of 500 nm were deposited on a commercially available ferritic alloy (Crofer 22APU) by large-area Pulsed Laser Deposition. The deposited samples were subsequently oxidized at 1173 K for 500 h in humidified air. The effects of the deposited thin films on the growth rate and the morphology of the oxide were investigated by weight gain measurements as well as by scanning electron microscopy. The growth of the oxide scales was reduced by both coatings, and most effectively by the LSC coating. The overall oxidation resistance and oxidation growth mechanism of the coated samples are discussed.

Thin films of the protein, lysozyme, have been deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Frozen targets of 0.3–1.0 wt.% lysozyme dissolved in ultrapure water were irradiated by laser light at 355 nm with a fluence of 2 J/cm2. The surface quality of the thin lysozyme films of different thickness deposited on 7 mm × 7 mm Si-〈1 0 0〉-wafers was investigated with scanning electron microscopy and atomic force microscopy. Already at comparatively low thickness, ∼20 nm, the substrate is covered by intact lysozyme molecules and fragments. The concentration of lysozyme in the ice matrix apparently does not play any significant role for the morphology of the film. The morphology obtained with MAPLE has been compared with results for direct laser irradiation of a pressed lysozyme sample (i.e. pulsed laser deposition (PLD)).

This work deals with the effect of Ni addition on the liquid–liquid phase separation in the Cu–Co system which displays a liquid metastable miscibility gap. Cu–Co–Ni samples with different compositions have been processed by differential scanning calorimetry using a fluxing technique to precisely determine transformation temperatures. The ternary phase diagram has been evaluated by Calphad, extrapolating the binary systems and optimizing ternary parameters using the experimental results of the present work. Ni additions reduce the demixing temperature, bringing the binodal line below the peritectic. The mechanisms of demixing and formation of microstructures have been clarified for low and high Ni content.

Some Cu-based alloys, like Cu–Co, Cu–Fe and Cu–Co–Fe, display a liquid metastable miscibility gap. When the melt is undercooled below a certain temperature depending on the alloy composition, they present a separation in two liquid phases, followed by coagulation before dendritic solidification. In order to predict the phase equilibria and the mechanisms of microstructure formation, a determination of the metastable monotectics in the phase diagrams is essential. This paper focuses on the up-to-date findings on the Cu–Co, Cu–Fe and Cu–Co–Fe metastable miscibility gap in the liquid phase. Furthermore, the knowledge on the phase equilibria in the three systems is extended by presenting new results obtained by differential scanning calorimetry (DSC) and comparing them with the calculated phase diagrams.

Matrix assisted pulsed laser evaporation (MAPLE) has been applied for deposition of thin polyethylene glycol (PEG) films with infrared laser light at 1064 nm. We have irradiated frozen targets (of 1 wt.% PEG dissolved in water) and measured the deposition rate in situ with a quartz crystal microbalance. The laser fluence needed to produce PEG films turned out to be unexpectedly high with a threshold of 9 J/cm2, and the deposition rate was much lower than that with laser light at 355 nm. Results from matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrate that the chemistry, molecular weight and polydispersity of the PEG films were identical to the starting material. Studies of the film surface with scanning electron microscopy (SEM) indicate that the Si-substrate is covered by a relatively homogenous PEG film with few bare spots.

Thin films of metals have been deposited in the large-area Pulsed Laser Deposition (PLD) Facility at Riso National Laboratory. Thin films of Ag and Ni were deposited with laser pulses from an excimer laser at 248 nm with a rectangular beam spot at a fluence of 10 J/cm2 on glass substrates of 127 mm diameter positioned 80 mm from the target in vacuum. We have explored the distribution of deposited material on a stationary substrate from a fixed point of impact on the target relative to the substrate. In all cases the angular distribution of the deposited metal layers shows a distinct “flip-over” of the plume. The thickness of the deposited films over the full area has been determined by energy-dispersive X-ray spectrometry in a scanning electron microscope (SEM). The measured distributions were then compared with analytical expressions. Finally, the angular distribution of the film thickness has been utilized in an algorithm for production of films over large areas.

La0.8Sr0.2Cr0.97V0.03O3 − δ (LSC) is commonly studied as a ceramic interconnect material as well as a coating material for metallic interconnects for solid oxide fuel cell applications. However, it is difficult to sinter this type of material to high density. In order to overcome this problem and to study the material in form of a thin film we have used Pulsed Laser Deposition to obtain a dense, uniform film with the right stochiometry. Investigation of preparation-parameter dependence of the LSC films deposited on a stainless steel substrate during pulsed-laser deposition was carried out. The LSC films were deposited with KrF excimer laser (248 nm) on a stainless steel substrate at different oxygen pressure and substrate temperatures. The substrate temperature (873–1073 K) and the oxygen background pressure (5–20 Pa) were varied in order to obtain optimal growth conditions. The surface morphology and structural information of the films were obtained using scanning electron microscope (SEM) and X-ray diffraction, respectively. Under the optimal preparation-parameter conditions: substrate temperature of 1023 K and an oxygen pressure of 10 Pa the structure of the film agreed with the target structure and the SEM micrographs show that the surfaces are homogeneous, smooth, crack-free and dense.

The small size of most of the present-day films produced by PLD (up to few cm2) is not only a general limiting factor for applications in many scientific and technical fields, but is also problematic for studies of samples for which edge effects may play an important role. Yttria-stabilized zirconia (YSZ) films with a uniform thickness have been deposited at different distances from the target and at different oxygen background pressure in the largearea PLD facility at Riso National Laboratory. Films of uniform thickness up to 300 nm and 1200 nm over an area with a diameter of more than 90 mm were achieved. Depending on the oxygen background pressure the YSZ films were found to grow in a highly oriented manner on the Si wafer.

The Cu–Co system displays a metastable miscibility gap in the liquid state. A considerable amount of work has been performed to study phase separation and related microstructures showing that demixing of the liquid is followed by coagulation before dendritic solidification. Due to kinetic competition of transformation phenomena, the mechanisms have not been fully disclosed. This contribution reviews such findings with the help of a computer calculation of the phase diagram and extends the present knowledge by presenting new results obtained by rapidly solidifying various Cu–Co compositions using a wide range of cooling rates achieved by forcing the liquid into cylindric and conic moulds and by melt spinning.

This paper deals with Co42Cu58 (at.%) alloy processed to obtain a cooling rate gradient during solidification. The Co–Cu system displays a metastable miscibility gap in the liquid state. Undercooling of the melt beyond a certain limit results in liquid separation and formation of droplets of the minority phase in a matrix of the dominant phase. The material was melted and cast in a wedge shaped copper mould to obtain a gradient of cooling rates. The cooling history of the alloy during the solidification was monitored by insertion of thermocouples at different positions in the mould. During cooling, the melt separated into droplets of Co-rich and Cu-rich phases. The Co-rich droplets are mainly coagulated along the major axis of the samples and an explanation of this segregation mechanism is proposed. The distribution of the size of the Co-rich particles was measured in various areas along the sample and correlated to the cooling rate.

Electrostatic gating provides a powerful approach to tune the conductivity of the two-dimensional electron liquid between two insulating oxides. For the LaAlO3/SrTiO3 (LAO/STO) interface, such gating effect could be further enhanced by a strong lattice polarization of STO caused by simultaneous application of gate field and illumination light. Herein, by monitoring the discharging process upon removing the gate field, we give firm evidence for the occurrence of this lattice polarization at the amorphous-LaAlO3/SrTiO3 interface. Moreover, we find that the lattice polarization is accompanied with a large expansion of the out-of-plane lattice of STO. Photo excitation affects the polarization process by accelerating the field-induced lattice expansion. The present work demonstrates the great potential of combined stimuli in exploring emergent phenomenon at complex oxide interfaces.

Pulsed Laser Deposition (PLD) of thin films of Cu2ZnSnS4 (CZTS) has not yet led to solar cells with high efficiency. The reason for the relative low efficiency is discussed and a way to overcome this issue is presented. The present thin film absorbers of CZTS suffer from loss of volatile Zn during the plasma-assisted transfer with PLD. This can be compensated by adding a thin layer of ZnS (∼ 80 nm) on top of the CZTS layer before the annealing. In this work the stack ordering of the two layers CZTS and ZnS is investigated, indicating that the configuration with ZnS on top of a CZTS film gives a better crystalline quality of CZTS after the annealing, as demonstrated by X-ray diffraction and Raman spectroscopy.

An enhanced thermal stability in thermoelectric Ca3Co4O9 thin films up to 550 °C in an oxygen rich environment was demonstrated by high-temperature electrical and X-ray diffraction measurements. In contrast to generally performed heating in helium gas, it is shown that an oxygen/helium mixture provides sufficient thermal contact, while preventing the previously disregarded formation of oxygen vacancies. Combining thermal cycling with electrical measurements proves to be a powerful tool to study the real intrinsic thermoelectric behaviour of oxide thin films at elevated temperatures. © 2015 AIP Publishing LLC.

A numerical model able to simulate solid-state constrained sintering is presented. The model couples an existing kinetic Monte Carlo (kMC) model for free sintering with a finite element model (FEM) for calculating stresses on a microstructural level. The microstructural response to the local stress as well as the FEM calculation of the stress field from the microstructural evolution is discussed. The sintering behavior of a sample constrained by a rigid substrate is simulated. The constrained sintering results in a larger number of pores near the substrate, as well as anisotropic sintering shrinkage, with significantly enhanced strain in the central upper part of the sample surface, and minimal strain at the edges near the substrate. All these features have also previously been observed experimentally., 9 pages, 7 figures

The discovery of two-dimensional electron gases (2DEGs) at the interface between two insulating complex oxides, such as LaAlO3 (LAO) or gamma-Al2O3 (GAO) epitaxially grown on SrTiO3 (STO) 1,2, provides an opportunity for developing all-oxide electronic devices3,4. These 2DEGs at complex oxide interfaces involve many-body interactions and give rise to a rich set of phenomena5, for example, superconductivity6, magnetism7,8, tunable metal-insulator transitions9, and phase separation10. However, large enhancement of the interfacial electron mobility remains a major and long-standing challenge for fundamental as well as applied research of complex oxides11-15. Here, we inserted a single unit cell insulating layer of polar La1-xSrxMnO3 (x=0, 1/8, and 1/3) at the interface between disordered LaAlO3 and crystalline SrTiO3 created at room temperature. We find that the electron mobility of the interfacial 2DEG is enhanced by more than two orders of magnitude. Our in-situ and resonant x-ray spectroscopic in addition to transmission electron microscopy results indicate that the manganite layer undergoes unambiguous electronic reconstruction and leads to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits clear Shubnikov-de Haas oscillations and the initial manifestation of the quantum Hall effect, demonstrating an unprecedented high-mobility and low electron density oxide 2DEG system. These findings open new avenues for oxide electronics., Comment: 29 pages, 5 figures, Accepted for publication in Nature Materials

Experimental results for an active magnetic regenerator (AMR) are presented. The focus is on whether or not it pays off to partly substitute soft magnetic material with non-magnetic insulation in a flux-conducting core in the magnet system. Such a substitution reduces losses due to heat conduction and eddy currents, but also reduces the magnetic field. Two different cores were tested in the AMR system with different cooling loads and it is shown, that in the present case, replacing half of the iron with insulation lead to an average reduction in temperature span of 14%, but also a small decrease in COP, hence the substitution did not pay off. Furthermore, it is shown experimentally, that small imbalances in the heat transfer fluid flow greatly influence the system performance. A reduction of these imbalances through valve adjustments resulted in an increase in the temperature span from approximately 16 K to 27.3 K.

Thin films of ZnS and Cu2SnS3have been produced by pulsed laser deposition (PLD), the latter for the firsttime. The effect of fluence and deposition temperature on the structure and the transmission spectrumas well as the deposition rate has been investigated, as has the stoichiometry of the films transferredfrom target to substrate. Elemental analysis by energy dispersive X-ray spectroscopy indicates lower Sand Sn content in Cu2SnS3films produced at higher fluence, whereas this trend is not seen in ZnS. Thedeposition rate of the compound materials measured in atoms per pulse is considerably larger than thatof the individual metals, Zn, Cu, and Sn.

Fuel cells convert chemical energy directly into electricity with high efficiency. Solid-oxide fuel cells (SOFCs) have the highest performance and durability. Traditional SOFCs operate at temperatures above 600 °C, and lowering the temperature to 400–500 °C is the key to new applications, for example, miniaturized systems with fast start/stop cycling and self-sustaining operation. A low-temperature SOFC is possible to achieve by tailoring the various cell components with thin-film technology. This chapter shows advantages and limitations in the use of thin films for SOFCs, in light of recent progress in the field.

In this paper, the relationship between the Gas to Melt Ratio (GMR) and the solid fraction of an evolving billet surface is investigated numerically. The basis for the analysis is a recently developed integrated procedure for modelling the entire spray forming process. This model includes the atomisation stage taking thermal coupling into consideration and the deposition of the droplets at the surface of the billet taking geometrical aspects such as shading into account. The coupling between these two models is accomplished by ensuring that the total droplet size distribution of the spray is the summation of “local” droplet size distributions along the r-axis of the spray cone. The criterion for a successful process has been a predefined process window characterised by a desired solid fraction range at a certain distance from the atomizer. Inside this process window, the gas and melt flows have been varied and their influence on the solid fraction at the surface of the billet has been analysed.

This article deals with the metastable liquid-liquid separation in the Cu-Co system. Several samples with different compositions were investigated by differential scanning calorimetry. High undercooling with respect to the liquidus was reached by means of the glass fluxing technique. The alloys were cycled with several heating and cooling runs in order to determine the temperature of the liquid-liquid separation and of the remixing. For each composition, demixing and remixing temperatures were found to be equal. Nucleation rate calculations of the liquid phase separation were carried out to explain the experimental results. The liquid-liquid separation in the Cu-Co system was found to be a nucleation process occurring with no detectable undercooling below the binodal line.