AnnaKarin Jonsson

Random conductivity of δ-Bi2O3 films

The experimental investigation of the cubic δ-Bi2O3 phase grown on a (110) Au substrate at low temperature has disclosed a chaotic character of the conductivity at low voltage and temperature. Based on first-principles calculations, we show that the conductivity of this oxide strongly depends on the distribution of oxygen ions and that oxygen migration is able to cause a momentary switch of the conduction mechanism.

Dielectric Permittivity and Intercalation Parameters of Li Ion Intercalated Atomic Layer Deposited ZrO2

Thin film devices for windows, mirrors, space applications and other purposes, have become an essential part of modern technology. A great advantage with a thin film device is the small amount of material used and the compact volume of the device. Dynamic control of thin film device properties is usually obtained by the application of a potential with a resulting charge transport. To understand this charge transport, thus become of great importance to improve, develop, and invent new thin film devices.Charge transport in transition metal oxide thin films and electrochromic devices have been studied in this thesis using dielectric and electrochemical methods. The dielectric methods used are impedance spectroscopy, the isothermal transient ionic current technique and current-voltage measurements. The electrochemical methods include the galvanostatic intermittent titration technique and electrochemical impedance spectroscopy.Ion intercalation parameters have been obtained for sputtered and ALD ZrO2 and sputtered TiO2, and the ion conduction processes have been analysed. The dielectric permittivity of as-deposited as well as intercalated thin films of ZrO2 and TiO2 have been studied and electron conduction mechanisms in as-deposited films deduced. From the impedance spectroscopy it is found that the dielectric response changes drastically upon ion intercalation. The complex dielectric response suggests different relaxation processes being important at different levels of intercalation and an explanation built on defect induced dipoles is proposed. Moreover, ion transport in electrochromic devices has been studied. The transient ionic current has been analysed to extract transport parameters both in single layers and whole devices and a deeper understanding of the ionic motion has been achieved.

H + Conduction in Solid-State Electrochromic Devices Analyzed by Transient Current Measurements

This paper presents an analysis of transient current measurements on an electrochromic device in order to evaluate the performance of the ion conductor and the average ion mobility in the device. A proton conducting all-thin-film device with WO 3 and hydrated NiO as the working and counter electrodes, respectively, and ZrO 2 as the ion conductor was studied. Potential reversal experiments were performed, and the resulting transient currents were measured and analyzed. The average proton diffusion coefficient for the whole device was found to be of the order of 10 - 1 4 cm 2 /s and the ZrO 2 layer was shown to be the rate-limiting layer.

Theoretical investigation of ion conduction in three-layered ion-conductor systems : Derivation of the isothermal transient ionic current and frequency-dependent impedance

Ion conduction in three-layered ion-conductor systems is considered. Explicit analytic expressions for the isothermal transient ionic current and frequency-dependent impedance are derived. The analysis includes migration, diffusion and space-charge effects as contributors to the ionic motion. The resulting model allows conduction parameters such as diffusion coefficients and ion concentrations in three different layers to be obtained from one single measurement, either in the time or in the frequency domain. The implications of one or more of the layers being mixed ionic/electronic conductors are discussed, and it is argued that the proposed model provides a useful description of the coupled ionic/electronic motion occurring in such a mixed-conductor system.

Dielectric study of thin films of Ta/sub 2/O/sub 5/ and ZrO/sub 2/

Electronic conduction in sputtered Ta/sub 2/O/sub 5/ and ZrO/sub 2/ thin films have been studied using impedance spectroscopy, isothermal transient ionic current, and current-voltage measurements. The dielectric properties of Ta/sub 2/O/sub 5/ were shown to be sensitively dependent on deposition parameters with two different frequency responses: a flat loss behavior with very low DC conductivity, or a relaxation peak together with a somewhat higher DC conductivity. ZrO/sub 2/ has different dielectric properties when fresh, i.e. newly deposited, or aged. A fresh sample arbitrarily can show two different behaviors, consisting of a DC conductivity with a relaxation peak superimposed on it. The DC conductivity shows either of two different values. The aged sample has a lower permittivity and DC conductivity, and the relaxation peak is found at much lower frequencies. Fresh samples of ZrO/sub 2/ also show switching behavior.