<p>Ceramic membranes made from mixed oxygen-ionic and electronic conducting perovskite oxides can selectively separate oxygen from air at elevated temperatures. These membranes have several potential applications that require a continuous supply of oxygen. For example, they may be an alternative for cryogenic production of oxygen or alternative electrode materials in solid oxide fuel cells. Of particular significance is the partial oxidation of methane to syngas (CO + H₂). By combining air separation and partial oxidation of natural gas into a single step, the need for expensive oxygen production by cryogenic means may be eliminated. Combined with existing processes for gas-to-liquid production such as Fisher-Tropsch and methanol synthesis, the MIEC membrane technology represents a very attractive route for conversion of natural gas to liquid fuels.</p><p>The research in this field was initially concerned with the search for materials with the optimum oxygen flux. Today, the long term stability of the membranes is probably the main issue. The membranes have to be stable under operating conditions, which include mechanical stability and chemically compatibility with other materials like sealing and support materials. However, the current understanding of the long term chemical and mechanical reliability is poor and this is one of the major challenges for solid state ionic research. The aim of this work has been to investigate the mechanical properties and the chemical stability of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0, 0.5, 1) materials when they are exposed to thermal and chemical gradients.</p><p>The chemically induced stresses due to reduction of the valence state of the transition metals are of particular importance with respect to the mechanical stability. In paper I, the oxygen non-stoichiometry, investigated by thermogravimetrical analysis, and thermal end chemical expansion, studied by dilatometry and high temperature X-ray diffraction, of La_0.5Sr_0.5Fe_1-xCo_xO3-δ materials are reported. The oxygen deficiency was observed to increase with decreasing partial pressure of oxygen and increasing temperature corresponding to expectations and previous reports. At ambient temperature the thermal expansion coefficient of the materials were in the range 15- 18·10^-6 K^-1. Above a certain temperature thermal reduction of the material take place, and the thermal expansion coefficient due to chemical expansion raise to 16-36·10^-6 K^-1. The chemical expansion ε_c, defined as the linear expansion due to a change in partial pressure of oxygen at constant temperature, reached a maximum in the range 0.036-0.039 for the materials studied at 800ºC. The change in ionic radii of the transition metals is the main contribution to the chemical expansion. The crystal structure of the perovskite materials were shown to be slightly rhombohedral at ambient temperatures and a transition to cubic phase were observed above 300ºC.</p><p>This non-linear thermal expansion behavior is a major challenge for the applications of the mixed conductor materials. La_0.5Sr_0.5Fe_1-xCo_xO_3-δ membranes in an oxygen partial pressure gradient will have different oxygen deficiency on either side of the membrane. The increasing oxygen deficiency is accompanied by a volume expansion as shown in paper I, and this will lead to chemically induced stresses. These stresses and the failure that might follow can be prevented by creep of the materials. Creep is also important due to dimensional stability. In paper II, the steady-state creep performance under compression of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0.5, 1) as a function of temperature, atmosphere, load and two different grain sizes is reported. The stress exponent found for the materials was close to unity and an unusual low inverse grain size exponent close to one was found for one of the materials. The activation energy of the two materials was not equal and the influence of secondary phases on the creep was discussed. The obtained creep behavior and microstructural investigation after measurements point to a diffusion related mechanism for the creep. Higher creep rates are found under reducing conditions and this suggest that creep relaxation of mechanical or chemical induced stresses may enhance the mechanical stability of oxygen permeable membranes.</p><p>In Paper III, the mechanical properties of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0.5, 0.75, 1) were investigated by several methods. Fracture strength was measured by four-point bending, fracture toughness was measured by SENB and SEVNB methods and finally Young’s modulus were investigated by four-point bending and resonant ultrasound spectroscopy. Four-point bending showed a non-linear ferroelastic behavior at ambient temperature due to rhombohedral crystal structure. Above the ferroelastic to paraelastic transition temperature the materials showed elastic behavior, however, at temperatures from about 800ºC a non-elastic respond was observed due to creep. The measured fracture strength and fracture toughness were observed to increase with increasing temperature, which was attributed to frozen-in stress gradients in the materials during cooling due to different oxygen stoichiometry. These stress gradients caused the low fracture strength and fracture toughness at ambient temperature. At higher temperatures, the stresses are assumed to relax resulting in a higher strength and fracture toughness. At high temperature, the non-linear respond made systematic errors in the calculated strength and fracture toughness. The Young’s modulus was measured from four-point bending and by resonant ultrasound spectroscopy for two of the materials. These data obtained by these two different methods were not in good agreement, which demonstrate the difficulty to obtain reliable data for the Young’s modulus of such materials by four-point bending. The presented findings have demonstrated the importance of understanding ferroelasticity and chemically induced stresses in order to comprehend the mechanical properties of such mixed valence state perovskite materials.</p><p>A high oxygen flux is required in order to realize the oxygen permeable membrane technology. At the same the chemical stability of the materials in a pO₂ gradient must be good for a sufficient long period of time. The oxygen flux performance and the long term stability of La_0.5Sr_0.5Fe_1-xCo_xO_3-δ (x = 0, 0.5, 1) are the topics of Paper IV and V.</p><p>Oxygen fluxes through the membranes are found as a function of oxygengradient and temperature in a oxygen permeation cell using air and inert gas on each side. The oxygen flux was observed to increase with decreasing pO₂on the secondary side until the surface exchange became rate limiting and the fluxes reach a constant value. By further increase of the pO₂ gradient, the flux seemed to decrease and this was attributed to the pO₂ dependence of the surface exchange coefficient. The apparent activation energy of the oxygen permeation was in good accordance with previous investigation of similar materials.</p><p>After about 5 week of exposure in an oxygen gradient at about 1150°C, the membranes were carefully examined by electron microscopy for evidence for kinetic demixing and decomposition. Dependent of the overall composition of the membrane, different secondary phases were formed at the primary surface of the membrane. For the cobalt containing materials, isolated grains or clusters of grains of cobalt oxide were formed. In case of the La_0.5Sr_0.5FeO_3-δ membrane, a dense and about 20 µm thick layer of the secondary phase SrFe₁₂O₁₉was formed at the primary side. The overall (La+Sr)/(Fe+Co) ratio was also seen to influence on the phase formed at the primary side. Kinetic demixing was also demonstrated in all the membranes although the metal concentration profiles were not drastically changed from the initial concentrations. The formation of secondary phases was reflected in the (La+Sr)/(Fe+Co) ratio across the membrane. The largest deviation from the nominal stoichiometry was seen close to the surfaces indicating steeper chemical gradients close to the surfaces. These phenomena may strongly limit the long term stability of thinner membranes e. g. films on a porous substrate.</p>

<p>This thesis deals with the preparation, optical characterization and analyses of experimental work and theoretical modeling on selective solar absorbers used in solar thermal collectors. The overall goal has been to obtain efficient absorbers by optimizing the optical properties, and to improve their durability using cost-effective techniques.</p><p>A Ni-Al₂O₃ absorber was pyrolytically coated with SnO₂ to improve its coating quality. Undesirable increase of solar reflectance obtained as a result of the SnO₂ was reduced by applying a silica antireflection layer produced by a dipping technique from colloidal silica sol. Annealing of Ni particles in an Al₂O₃ matrix was also carried out and compared to particles heated without the matrix. Due to the Al₂O₃ matrix, a much slower oxidation rate was found for the embedded particles. In addition, the optical performance of commercial Ni-Al₂O₃ and Ni-NiO_x absorbers were experimentally compared at oblique incidence. A better solar-absorptance of the Ni-Al₂O₃ at higher angles of incidence was found. This is due to enhanced optical interference in the double-layer structure of Ni-Al₂O₃, which could not be achieved in the graded index film of Ni-NiO_x.</p><p>The optical properties of Si-Al₂O₃ films of different thicknesses have been investigated by preparing the films using an integral coloration method. The solar-absorptance and thermal-emittance were found to increase with increasing film thickness. Due to high thermal-emittance, the Si-Al₂O₃ coating shows non-selective absorbing properties. Its feasibility for a selective solar absorber was studied by modeling the coating as a function of coating thickness for different particle size and volume fraction using four-flux theory. The results indicated that the Si-Al₂O₃ coating is not a suitable candidate for selective solar absorbers.</p><p>Scattering and absorption cross-sections of FeMnCuO_x and black carbon pigments have been obtained from reflectance and transmittance measurements in the solar wavelength range. The cross-sections were determined by using pellets consisting of low pigment volume fractions dispersed in KBr matrix. The cross-sections exhibit linear dependence of the volume fraction, indicating that single scattering dominates. The cross-sections were used to model the optical properties of solar selective paints using four-flux model resulting in good agreement between calculations and experiments.</p>

<p>An angle-resolved scatterometer and an integrating sphere for reflectance measurements at oblique angles of incidence have been designed and evaluated. The integrating sphere has a centre-mounted sample holder and the detector sits at the end of the sample holder and therefore always faces the same sphere wall area. The sphere geometry plays an important role for the modelling of detected signals and the reflected intensity has to be divided into a specular and a diffuse component. These components must be treated separately in the modelling. These two instruments, as well as traditional spectrophotometers, have been used for the evaluation of solar energy materials. Scattering as well as non-scattering surfaces have been studied, requiring different measurement techniques.</p><p>By using angle-resolved scatterometry it has been demonstrated that a solar reflector does not need to be perfectly specular provided the concentration factor is low. Thus it is possible to use inexpensive aluminium foil as the reflector material. The possibility of increasing the reflectance of aluminium with thin dielectric films of silicon and titanium oxides for pv-cell and solar thermal collector application has been investigated. Particular attention has been paid to the angular optical properties since thin films strongly affect them owing to interference effects. In an under-glazing application for pv-cells, the use of aluminium coated with titania and silica is recommended. The long-term stability of several reflector materials has been studied and anodised aluminium protected by a UV-stabilised polymer coating is recommended for solar collector reflectors.</p><p>Antireflective films consisting of porous silicon oxide for solar collector cover glazings have been studied. The films were prepared by a dip-coating process using a suspension of nano-sized silicon oxide particles. This treatment increased the solar transmittance by 5.5 percentage points. It has also been shown that it is possible to temper antireflection treated glazings without seriously affecting the optical performance. The tempering also strongly improves the mechanical stability of the film.Some of the measurements presented in this thesis were used as input data to simulation programs, which calculate the collected annual energy as a function of the optical properties of the different components. It was found that spectrophotometric laboratory measurements agree well with outdoor collector testings.</p>

<p>During recent decades, huge amount of radioactive waste has been dumped into the earth's surface environments. ¹²⁹I (T_1/2= 15.6 My) is one of the radioactive products that has been produced through a variety of processes, including atomic weapon testing, reprocessing of nuclear fuel and nuclear accidents. This thesis describes development of the Accelerator Mass Spectrometry (AMS) ultra-sensitive atom counting technique at Uppsala Tandem Laboratory to measure ¹²⁹I and discusses investigations of its distribution in the hydrosphere (marine and fresh water) and precipitation. The AMS technique provides a method for measuring long-lived radioactive isotopes in small samples, relative to other conventional techniques, and thus opens a new line of research. The optimization of the AMS system at Uppsala included testing a time of flight detector, evaluation of the most appropriate charge-state, reduction of molecular interference and imporvement of the detection limit. Furthermore, development of a chemical procedure for separation of iodine from natural water samples has been accomplished. </p><p>The second part of the thesis reports investigations of ¹²⁹I in natural waters and indicates that high concentrations of ¹²⁹I (3-4 orders of magnitude higher than in the pre-nuclear era) are found in most of the considered natural waters. Inventory calculations and results of measurements suggest that the major sources of radioactive iodine are the two main European nuclear reprocessing facilities at Sellafield (U.K.) and La Hague (France). This information provides estimates of the transit time and vertical mixing of water masses in the central Arctic Ocean. Results from precipitation, lakes and runoff are used to elucidate mechanisms of transport of ¹²⁹I from the point sources and its pathways in the hydrological environment. This study also shows the need for continuous monitoring of the ¹²⁹I level in the hydrosphere and of its future variability.</p>

<p>By the introduction of machine elements made of light metals, e.g. Al or Mg alloys, which are coated with a material providing high wear resistance and low friction coefficient, both economical and environmental benefits can be gained. A high resistance against wear results in increased lifetime and lower costs for spare parts and maintenance. This also means fewer production stops and less machine downtime. Moreover, a vehicle of lower weight and with reduced friction losses will consume less fuel.</p><p>The light metal alloys display low hardness and elastic modulus and in addition they have a high tendency to stick to the countersurface in sliding contact. Hence, to be used in tribologically demanding applications, they must be coated with a material providing low friction and wear. Due to the thin and brittle nature of the available coatings an intermediate load-carrying layer has to be introduced to protect the base material from large deformations and the brittle surface coating from cracking.</p><p>In this thesis both experiments and theoretical simulations has shown that the load-carrying layer between the soft and compliant base material and the thin brittle coating should have high elastic modulus and hardness as well as a for the contact situation sufficient thickness.</p><p>A number of vapour deposited coatings have been investigated regarding their tribological behaviour with special emphasis on the mechanisms providing low friction. When sliding against steel, it was found that carbon-rich coatings show much lower friction and wear of the countersurface than nitrogen-rich coatings. The explanation is that steel has a tendency to stick to nitrogen-rich coatings, leading to steel against steel contact, but not to carbon-rich coatings. Another explanation is that material is transferred from a carbon-rich coating to the steel and this gives an easily sheared contact with low friction coefficient.</p>

<p>This thesis deals with studies of thin films using soft x-ray emission spectroscopy. Thin films are frequently used in optical, semiconductor and magnetic applications, and along with the development of thin film deposition techniques, there is a growing need for thin film characterisation and production control. Soft x-ray spectroscopy provides elemental as well as chemical bonding information and has the advantage of being relatively insensitive to electric and magnetic fields. It may thus be used <i>in-situ</i> during deposition for monitoring sputtering deposition.</p><p>Thin films of TiVN were reactively co-sputtered using two targets, and soft x-ray spectroscopy and optical emission spectroscopy were used to determine the film composition <i>in-situ</i>. These measurements were compared with <i>ex-situ </i>elemental analysis<i> </i>as well as with computer simulations. The results agree qualitatively and indicate that soft x-ray spectroscopy can be used for <i>in-situ</i> determination of film composition. In another study, the composition of chromium nitride was studied <i>in-situ</i> under varying deposition conditions. The fraction of different stoichiometric phases in the deposited films as a function of nitrogen flow was determined <i>in-situ</i>.</p><p>The thesis also deals with the angular dependence of soft x-ray emission spectroscopy. The angular dependence of the emission was measured and compared to simulations for layered samples consisting of different transition metals, one sample consisting of Fe(50Å)/Cu(100Å)/V(100Å)/Si and another set of samples consisting of Fe(XÅ)/V(100Å)/MgO, where X = 25, 50 and 100 Å. The measured angular variation can be described qualitatively by calculations including refractive effects. For measurements below the critical angle of reflection, only the top layer corresponding to the evanescent wave region of 20-50 Å is probed, whereas for larger grazing angles the probe depth reaches thousands of Å. This demonstrates the feasibility of using the angular dependence as a way of studying composition and layer thickness of thin films.</p>

<p>This thesis treats angle-resolved optical properties and the energy efficiency of windows. A theoretical evaluation of optical and thermal properties of windows is briefly surveyed and the energy performance of a large selection of windows, under different conditions, is examined. In particular, angle dependent optical properties are analysed. A new model assessing angle dependence of the total solar energy transmittance, g, of windows is presented. A comparison of simple models for angle-dependence prediction has been performed, including both fictitious and measured real window glazings. The new proposed model illustrates low errors for both the real and the fictitious glazings. The impact of inaccuracy in the angle dependence of the g-factor has been assessed and found to be clearly noticeable but not necessarily critical. </p><p>A simple model for comparing the energy efficiency of different windows in different types of buildings and different climates has been further developed and analysed for several conditions. The energy performance of a large number of windows has been analysed using this model, and also by using other building and window simulation models. Typical savings when changing from a standard double glazed window to the optimal window for the investigated case is in the order of 100-150 kWh/m²yr. The annual energy balance of modern low emittance windows illustrates that they can be annual energy savers rather than energy losers, unlike traditional windows. However, it is shown that it is not important to argue about small changes (~0.01) of the thermal emittance value. Furthermore, advance solar control glazings effectively reduce solar transmittance with maintained high light transmittance. </p><p>AR-coatings and low-iron glazings can increase the transmittance of glazings considerably. In fact, a "super" low emittance window with a U-value below 1 W/m²K can have higher light transmittance than a common double-glazed unit. Windows with variable transmittance, switchable windows, are compared with high-performing solar control windows, illustrating some degree of potential energy savings compared to high performing static solar control windows, depending on the type of control that is used. This is accompanied by the potential for automatic thermal comfort- and glare control. </p><p>Different models for energy rating of windows have been evaluated, demonstrating that a simple linear rating depending on the U and g-factor of the window may be sufficient with certain restrictions. Division into climate zones is essential. </p><p>In all, the results demonstrate that energy-efficient windows provide huge energy-saving potentials on a large (regional, national, global) scale. </p>

<p>Magnetic properties of nanoparticle systems and spin glasses have been investigated theoretically, and experimentally by squid magnetometry.</p><p>Two model three-dimensional spin glasses have been studied: a long-range Ag(11 at% Mn) Heisenberg spin glass and a short-range Fe_0.5Mn_0.5TiO₃ Ising spin glass. Experimental protocols revealing ageing, memory and rejuvenation phenomena are used. Quantitative analyses of the glassy dynamics within the droplet model give evidences of significantly different exponents describing the nonequilibrium dynamics of the two samples. In particular, non-accumulative ageing related to temperature-chaos is much stronger in Ag(11 at% Mn) than in Fe_0.5Mn_0.5TiO₃.</p><p>The physical properties of magnetic nanoparticles have been investigated with focus on the influence of dipolar interparticle interaction. For weakly coupled nanoparticles, thermodynamic perturbation theory is employed to derive analytical expressions for the linear equilibrium susceptibility, the zero-field specific heat and averages of the local dipolar fields. By introducing the averages of the dipolar fields in an expression for the relaxation rate of a single particle, a non trivial dependence of the superparamagnetic blocking on the damping coefficient is evidenced. This damping dependence is interpreted in terms of the nonaxially symmetric potential created by the transverse component of the dipolar field.</p><p>Strongly interacting nanoparticle systems are investigated experimentally in terms of spin-glass behaviour. Disorder and frustration arise in samples consisting of frozen ferrofluids from the randomness in particle position and anisotropy axes orientation. A strongly interacting system is shown to exhibit critical dynamics characteristic of a spin-glass phase transition. Ageing, memory and rejuvenation phenomena similar to those of conventional spin glasses are observed, albeit with weak temperature-chaos effects.</p>

<p>Magnetic and electrical properties of selected compounds containing manganese (Mn) are investigated by SQUID magnetometry and transport measurements.</p><p>(Ga,Mn)As is a magnetic semiconductor obtained from GaAs by substituting Ga³⁺ for Mn²⁺. Mn acts in the alloy as a magnetic impurity, as well as a hole dopant. A carrier mediated ferromagnetic interaction is observed in (Ga,Mn)As single layers, as well as in (Ga,Mn)As/GaAs superlattices. The magnetic and electrical properties of these structures are controlled by the amount of holes, and thus by the amount of compensating defects such as As_Ga antisites. Magnetic inhomogeneity appears for thin layers as well as for layers containing large concentration of Manganese.</p><p>In non magnetic metallic elements containing a small amount of manganese impurities, a magnetic interaction develops, oscillating in sign with the distance between Mn atoms. Due to random distribution of manganese in a Ag(Mn) alloy, competing ferromagnetic and antiferromagnetic interaction appears, yielding magnetic frustration and the appearance of a spin glass phase at low temperature. These disordered systems show aging, chaos and memory phenomena, which are investigated in the three dimensional Ag(Mn) and Fe_0.5Mn_0.5TiO₃ spin glasses using time dependent magnetization measurements.</p><p>Perovskite manganites of type (R³⁺_1-xA²⁺_x)MnO₃ show colossal magnetoresistive e_ects (CMR). For an optimum doping x, a ferromagnetic order is established, and large changes of their electrical resistance with an applied magnetic field are observed; a magnetoresistance which can be tailored by adding oriented grain boundaries in thin films of these materials. The Manganese appears in the system as Mn³⁺ and Mn⁴⁺, and both ferromagnetic and antiferromagnetic interaction is mediated by the charge carriers along the Mn-O-Mn bonds of the perovskite structure. Depending on the cations forming the manganite, and their relative amount, glassy dynamics may appear, yielding aging and memory features similar to those observed in spin glasses.</p>

<p>This thesis treats charged particle transport, mostly in solid materials but also, to some extent, in aqueous media. Three major types of materials have been investigated; dielectric materials, ion conductors, and drug-delivery systems.</p><p>The frequency-dependent dielectric permittivity of sputtered amorphous thin film tantalum oxide (Ta₂O₅) has been determined by using impedance spectroscopy. A new interpolation formula has been derived, that interpolates between the two power-law regions at low and high frequencies usually observed in the dielectric spectrum. This formula is based on a regular-singular-point (RSP) analysis of the conduction process, and the power-laws in the dielectric spectrum are interpreted in terms of RSPs of the underlying rate equation for the corresponding polarization-current response function.</p><p>Lithium transport properties of Ta₂O₅ have been analyzed by using the galvanostatic intermittent titration technique and by isothermal transient ionic current measurements. Chemical and component diffusion coefficients for intercalated lithium have been extracted. Moreover, the ion conduction process has been analyzed theoretically, and expressions for transient ionic currents derived, both for single ion-conducting layers and for three-layered structures of ion conductors.</p><p>Electrical measurement techniques have also been applied to pharmaceutical systems. The alternating ionic current technique has been developed as a tool for determining the release of electrically charged drug substances in aqueous media. Tablets made of agglomerated micronized cellulose have been investigated, and sodium chloride has been used as a model drug. An attempt has been made to describe the combined drug dissolution and drug release processes in mathematical terms.</p>