| 1. |
- Granqvist, C.-G., et al.
(författare)
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Recent advances in electrochromics for smart windows applications
- 1998
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Ingår i: Solar Energy. - 0038-092X .- 1471-1257. ; 63:4, s. 199-216
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr-Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto-chronopotentiometry data in Zr-Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr-Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto-chronopotentiometry data in Zr-Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.
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| 2. |
- Granqvist, Claes-Göran, et al.
(författare)
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Towards the smart window : progress in electrochromics
- 1997
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Ingår i: Journal of Non-Crystalline Solids. - 0022-3093 .- 1873-4812. ; 218, s. 273-279
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Tidskriftsartikel (refereegranskat)abstract
- Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.
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| 3. |
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| 4. |
- Isidorsson, Jan, et al.
(författare)
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Physical and Electrochemical properties of Li-intercalated Sn oxide films made by sputtering
- 1995
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Ingår i: Ionics (Kiel). - 0947-7047 .- 1862-0760. ; 1:5-6, s. 400-405
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Tidskriftsartikel (refereegranskat)abstract
- Sn oxide films were made by reactive rf magnetron sputtering under conditions that led to both electronic and ionic conductivity. The film structure was studied by X-ray diffraction and Atomic Force Microscopy (AFM). Li+ intercalation produced electrochromism with coloration efficiency peaked in the infrared. Cyclic voltammograms taken at different sweep rates were interpreted in terms of a unique structural parameter related to the fractal dimension of a self-affine surface relief and in excellent agreement with the fractal dimension as obtained with AFM. Mössbauer spectroscopy was used to determine the valence state of the Sn-atoms; a change from Sn4+ to Sn2+ was detected after electrochemical intercalation of Li+.
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| 5. |
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| 6. |
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| 7. |
- Strömme, Maria, et al.
(författare)
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Determination of fractal dimension by cyclic I-V studies: The Laplace-transform method
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52:19
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Tidskriftsartikel (refereegranskat)abstract
- A method is introduced for the determination of fractal dimension df from cyclic voltammograms taken on films in contact with an electrolyte. It is based on a Laplace transform of the Nernst equations using Riemann-Liouville transform expressions for the surface concentrations. Diffusion-limited conditions are required. The method is applicable even when resistance drops are present in the electrolyte or across the film. Our Laplace transform method gave correct results for gold electrodes with known df and it also provided a fractal dimension of a partially active In oxide surface in good agreement with that obtained from an independent technique.
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| 8. |
- Strömme, Maria, et al.
(författare)
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Diffusion of Li, Na and K in fluorinated Ti dioxide films : Applicability of the Anderson-Stuart Model
- 1997
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 81, s. 2167-2172
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Tidskriftsartikel (refereegranskat)abstract
- Fluorinated Ti dioxide films were made by reactive sputtering. The mobility of Li, Na, and K in this host was studied by electrochemical techniques. Chronopotentiometry suggested that the cations occupy one type of site for cation/Ti ratios below 0.5, and that other sites are populated at higher ratios. Li and Na intercalation appeared to progress without major structural changes, whereas the intercalation of the larger K ions caused structural rearrangement. Impedance spectra were interpreted within a Randles circuit with a finite length Warburg element from which chemical diffusion coefficients were obtained at different intercalation levels and temperatures. The ion diffusion could be understood in detail from the classical Anderson–Stuart model [O. L. Anderson and D. A. Stuart, J. Am. Ceram. Soc. 37, 573 (1954)] as long as the structure remained unchanged, i.e., for the Li and Na intercalation, whereas K intercalation, expectedly, could not be reconciled with this model.
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| 9. |
- Strömme, Maria, et al.
(författare)
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Fractal dimension of Li insertion electrodes studied by diffusion-controlled voltammetry and impedance spectroscopy
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 2968-2971
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Tidskriftsartikel (refereegranskat)abstract
- We show that a unique fractal dimension can be obtained for Li insertion electrodes by applying two different electrochemical methods to samples of porous Sn oxide and Ti oxide. The first method relies on the assumption that the current recorded in voltammetric experiments, conducted in a Li containing electrolyte, is limited by Li diffusion from the fractal working electrode surface into the oxide matrix. The second method is based on the capacitance dispersion observed in impedance spectroscopy. Simple scaling arguments show that this capacitance dispersion is related to the fractal structure of surface roughness
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| 10. |
- Strömme, Maria, et al.
(författare)
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Fractal surface dimension from cyclic I-V studies and Atomic Force Microscopy; Role of non-contiguous reaction sites
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:24, s. 17884-17887
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Tidskriftsartikel (refereegranskat)abstract
- Films of In oxide and Sn oxyfluoride were made by magnetron sputtering and spray pyrolysis, respectively. Cyclic voltammetry on films in contact with an electrolyte, and atomic-force microscopy (AFM) on as-deposited films, showed that the fractal dimension obtained from the voltammetric peak-current technique is in excellent agreement with the fractal hillock distribution received via the mass-radius method applied to thresholded AFM images.
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| 11. |
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| 12. |
- Strömme, Maria, et al.
(författare)
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Impedance spectroscopy on lithiated Ti oxide and Ti oxyfluoride thin films
- 1996
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 79, s. 3749-
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Tidskriftsartikel (refereegranskat)abstract
- Films of Ti oxide and Ti oxyfluoride were produced by reactive magnetron sputtering of Ti in Ar+O2(+CF4). Compositional and structuralanalyses were accomplished by Rutherford backscattering spectrometry, x‐ray diffraction(XRD), infrared absorption spectrometry, and atomic force microscopy(AFM).Electrochemical characterization of films immersed in a Li conducting electrolyte was performed with cyclic voltammetry and coulometric titration. Detailed impedance spectra were recorded for the 2×105–1×10−3 Hz range. The impedance responses of pure and fluorinated Ti oxide films in the lithium containing electrolyte differed significantly even if their structures, according to AFM and XRD, were very similar. One main difference was the size of the charge transfer resistance, presumably connected to the Li ion injection from the electrolyte into the film. A modest fluorination lowered this resistance by about two orders of magnitude. The voltammetric and the impedance responses, as well as the magnitude of the chemical diffusion coefficient, of the fluorinated Ti oxide film were strikingly similar to the response of WO3films. This similarity does not occur for the pure Ti oxide films, where a process, believed to be the Li ion injection, could be identified with the main features of the frequency‐dependent impedance. Underlying this charge transfer mechanism, however, a process represented by a constant phase element seems to be operating. This latter process may have its origin in Li diffusion into the film.
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| 13. |
- Strömme, Maria, et al.
(författare)
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Impedance studies on Li insertion electrodes of Sn oxide and oxyfluoride
- 1996
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 80:1, s. 233-241
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Tidskriftsartikel (refereegranskat)abstract
- Films of Sn oxide and oxyfluoride were made by reactive rf magnetron sputtering onto ITO‐coated glass. We analyzed the composition by Rutherford backscattering spectrometry, the structure by x‐ray diffraction, and the surfacetopography by atomic force microscopy. Li intercalation from a liquid electrolyte was more facile in the oxide than in the oxyfluoride, as found from cyclic voltammetry. Impedance spectra were taken for a wide range of frequencies and polarizing voltages. Nyqvist diagrams were interpreted from a circuit model with elements representing Li insertion at the electrolyte/film interface and electron insertion at the film/ITO interface. The data were consistent with a fractal surface of the Sn oxide film, with a dimension in excellent agreement with measures obtained through several independent techniques. The chemical diffusion coefficient was ∼10−13 cm2/s and slightly decreasing with increasing potential for all films.
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| 14. |
- Strömme, Maria, et al.
(författare)
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Li diffusion in Ti oxyfluoride films : Thermal activation energy and jump length derived from impedance spectroscopy
- 1996
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 80:4, s. 2169-2174
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Tidskriftsartikel (refereegranskat)abstract
- Li ions were electrochemically intercalated into sputtered Ti oxyfluoride films. The process was found to be thermally activated with an activation energy depending on the amount of intercalated Li and decreasing with increasing Li content. The chemical diffusion coefficient was thermally activated as well with an activation energy of ∼0.5 eV independent of the amount of intercalated Li. The origin of the activation energy was discussed in terms of the Anderson–Stuart model. It was found likely that strain energy is needed to open up ‘‘doorways’’ in the Ti oxyfluoride structure to allow Li ion transport. The jump length for the Li ions inside the Ti oxyfluoride was estimated to lie in the 4–8 Å interval.
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| 15. |
- Strömme, Maria, et al.
(författare)
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Li intercalation in transparent Ti-Ce oxide films : Energetics and ion dynamics
- 1997
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 81:9, s. 6432-6437
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Tidskriftsartikel (refereegranskat)abstract
- Films of Ti dioxide, mixed Ti–Ce oxide, and Ce dioxide were produced by reactive dc magnetron sputtering.Electrochemical lithiation was probed by chronopotentiometry, cyclic voltammetry together with optical transmittance recording, and impedance spectroscopy. Evidence was found for inserted electrons being accommodated in Ce4f states; this contention was supported by preliminary results from x-rayabsorption fine-structure spectroscopy. These electrons do not produce luminous electrochromism. The variation of the chemical diffusion coefficient of Li, with film composition and Li content, was also studied.
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| 16. |
- Strömme, Maria Mattsson, et al.
(författare)
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A frequency response and transient current study of beta-Ta2O5 : Methods of estimating the dielectric constant, direct current conductivity, and ion mobility
- 1999
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 85
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric ac measurements in the frequency range of ∼1 mHz–1 MHz were performed on β-Ta2O5 samples made by chemical vapor deposition. A method of estimating the dielectric constant and the dc conductivity from the dielectric response was developed. The high-frequency dielectric constant was found to be 25.84 with no detectable temperature dependence and the dc conductivity due to protons had an activation energy of about 0.4 eV in the studied temperature range (from 24 to 90 °C). Evidence for the conduction mechanism being protonic rather then electronic was found from isothermal transient ionic current (ITIC) measurements. The ITIC recordings could also determine conduction parameters, such as protonmobility, number of charge carriers, and dc conductivity.
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| 17. |
- Strömme, Maria Mattsson, et al.
(författare)
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Isothermal transient ionic current as a characterization technique for ion transport in Ta2O5
- 1999
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 85:12, s. 8199-8204
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Tidskriftsartikel (refereegranskat)abstract
- The Isothermal Transient Ionic Current (ITIC) technique was applied to β-Ta2O5 samples made by chemical vapor deposition. The mobility, conductivity, and number of protons in the material could be extracted from the measurements. Li ions were intercalated electrochemically into the β-Ta2O5 and it was found that the ITIC method could separate the contribution from proton and Li ion conduction in such a way that the mobilities of both species could be extracted. Furthermore, the lattice-gas model [A. J. Berlinsky, W. G. Unruh, W. R. McKinnon, and R. R. Haering, Solid State Commun. 31, 135 (1979)] was employed to describe the Li interaction process. This model showed that the Li ions tended to distribute uniformly, rather then to attract each other and form clusters in the material.
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| 18. |
- Strömme, Maria, et al.
(författare)
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Optical constants of sputtered hafnium nitride films. Intra- and interband contributions
- 1995
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Ingår i: Optical materials (Amsterdam). - : Elsevier BV. - 0925-3467 .- 1873-1252. ; 4:5, s. 629-639
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Tidskriftsartikel (refereegranskat)abstract
- Transparent and opaque films of hafnium nitride have been prepared by reactive magnetron sputtering in an argon-nitrogen atmosphere. The films were deposited upon heated Coming glass substrates with a deposition rate of about 2.1 nm/s. The optical constants of the films were calculated using Kramers-Kronig integration and ellipsometry for the opaque samples and a combined method for transparent samples. Detailed observation of the thickness variation in the optical constants revealed a clear trend: larger n-values and smaller k-values in the VIS-and NIR-range for thinner films. This was analysed within the framework of the classical Drude model and found to be an effect of shorter relaxation time for thinner films. The effect is as large as a factor of three in the film thickness interval 15–380 nm. The optical effective mass of the d-electrons was found to be in the interval 0.82–0.95 of the free electron mass, which is significantly lower than in TiN but similar to ZrN. The interband contribution to ϵ2(ω) was obtained by subtraction of the Drude part from the experimental dielectric function. It exhibits a sharp increase for λ < 400 nm, indicating the threshold for interband transistion.
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| 19. |
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| 20. |
- Strömme, Maria, et al.
(författare)
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Voltammetry on fractals
- 1995
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Ingår i: Solid State Communications. - : Elsevier BV. - 0038-1098 .- 1879-2766. ; 96:3, s. 151-154
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Tidskriftsartikel (refereegranskat)abstract
- New methods are introduced for determining the fractal dimension df of a surface from cyclic voltammograms. The separation between current peaks is strongly dependent on df, provided that the current is diffusion limited. We also derive a new Randles-Sevcik equation-relating the diffusion coefficient to the peak current of a voltammogram—that holds for electrodes with fractal surfaces. This equation gives a simple additional method of determining df from voltammetry using recordings of the peak current at different scan rates.
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| 21. |
- Strømme Mattsson, Maria
(författare)
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Cation intercalation and surface fractality in metal oxide based films
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- New methods have been developed for determining the fractal dimension df of asurface from cyclic voltammograms with the sample of interest serving as the workingelectrode in an electrochemical cell. The methods have been verified by applying them tovoltammograms recorded on gold samples with a well-defined fractal dimension.Agreement between the "voltammetry dimension" and the dimension obtained fromatomic force microscop on various metal oxide surfaces has been established.Cation insertion electrodes have been studied by different electrochemical and physical techniques, and it has been shown that a unique fractal dimension can be obtained for such electrodes from diffusion-limited voltammetry and from the capacitance dispersion observed in impedance spectroscopy.From temperature dependent impedance spectroscopy, it was found that diffusion ofLi, Na, and K ions in a Ti dioxide based host was thermally activated. The experimentalactivation energies were analysed using the classical Anderson-Stuart method as well as aquantum-chemical intermediate neglect of differential overlap method. The effect offluorine doping of Ti as well as Sn oxide films was also investigated.The electron density of states in mixed Ti-Ce and mixed Zr-Ce oxide films werestudied by electrochemical techniques, and the Ce4f states were found to account for thedecreasing electrochromism in the Ti-Ce oxide films, as well as for the increased chargecapacity in the Zr-Ce oxide films in comparison with the pure transition metal oxides.
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| 22. |
- Veszelei, Monica, et al.
(författare)
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Optical and electrochemical properties of Li+ intercalated Zr-Ce oxide and Hf-Ce oxide films
- 1998
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 83:3, s. 1670-1676
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Tidskriftsartikel (refereegranskat)abstract
- Sputter deposited Zr–Ce oxide and Hf–Ce oxide films were investigated with regard to structure,optical absorption, and electrochemicalproperties.X-raydiffractometry and Rutherford backscattering spectrometry showed that polycrystalline Zr–Ce oxide and Hf–Ce oxide films had cubic crystal structures for 40–100 mol % CeO2 and 50–100 mol % CeO2, respectively. Cyclic voltammetry was performed in an electrolyte of propylene carbonate containing LiClO4. The charge capacity was ∼60mC/cm2μm for a Zr–Ce oxide film with a Ce/Zr atom ratio of ∼13 as well as for a Hf–Ce oxide film with a Ce/Hf atom ratio of ∼2. A decrease of the charge capacity was noted after ∼1000 voltammetric cycles, with the mixed oxide films being far more stable than CeO2. In situ optical transmittance measurements showed that both Zr–Ce and Hf–Ce oxide films remained essentially transparent during Li+ intercalation. Chronopotentiometry measurements were used to elucidate effects of the electronic structure during Li+ intercalation.
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| 23. |
- Veszelei, M, et al.
(författare)
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Zr-Ce Oxides as Candidates for Optically Passive Counter Electrodes
- 1999
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Ingår i: Solar Energy Materials and Solar Cells. - 0927-0248 .- 1879-3398. ; 56:3-4, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- Zr-Ce oxide films with compositions from pure Zr oxide to pure Ce oxide were made by reactive DC magnetron co-sputtering. The composition and structure were determined by Rutherford backscattering and X-ray diffraction. Pure Ce oxide films have high charge capacity and are optically passive under charge insertion; they are, however, chemically unstable in an electrolyte of LiClO4 in propylene carbonate. Pure Zr oxide has practically zero charge capacity. Zr-Ce oxide films have high (above 80%) optical transmittance, high charge capacity, and good chemical stability. These films remain fully transparent irrespective of their degree of lithiation, which may be reconciled with electrons accommodating 4f states of Ce.
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