Y. Danto

Influence of oxygen on electrical properties of βPbF2 thin films

Abstract In this paper, a study of oxygen adsorption by βPbF 2 thin films is presented. In a first part, results of oxygen analysis by nuclear methods and by ESCA are presented. Then, the influence of oxygen on both interfacial and bulk electrical properties is studied. Besides a slow diffusion process in the film, the results seem to show the presence of a thin oxidized layer at the surface.

A Pb|PbF2|BiF3|Bi thin solid film reversible galvanic cell

Abstract Thin film solid state galvanic cells were made using leas as the anode, PbF 2 as the electrolyte and BiF 3 |Bi as the cathode. The cells were obtained by charging a simple Bi|PbF 2 |Bi structure. Such elements develop open-circuit voltages of 353 mV, in good agreement with the theoretical value. The discharge characteristics show a plateau region of several hours. At room temperature current densities of 40 μ A cm -2 were measured with voltages of about 200 mV. Short-circuit currents larger than 1 mA cm -2 were obtained. The cells are entirely reversible, and many complete charge-discharge cycles were performed. The evolution of the d.c. internal resistance as a function of discharge is discussed.

A.c. study of metal-β-PbF2-metal thin film structures

Abstract The electrical properties of the ionic conductor β-PbF 2 were studied using admittance and impedance diagrams. Measurements were made on symmetrical metal-β-PbF 2 -metal thin film structures which were obtained by thermal evaporation in vacuum. It was possible to distinguish between bulk and interfacial properties. The conductivity of the PbF 2 films is compared with that obtained for bulk samples. A description of the interfacial layer between the electrode and the solid electrolyte is given.

A study of thermally stimulated currents in thin films of a good ionic conductor (βPbF2) with blocking electrodes

Abstract Thin film samples of βPbF2 are studied by stimulated currents, the TSC peak of lower temperature, independent of the polarization voltage is attributed to the space charge depolarization. On the basis of simplifying hypothesis an exact analytical solution of this problem is also proposed; the comparison with the experimental results allows to get a value of the activation energy of mobile species and to estimate the thickness of the space charge. Electron transfers at the electrodes are assumed to explain the second peak.

Investigation of a metal-ionic conductor interface in thin film samples using X-ray photoelectron spectroscopy and electrical measurements

Abstract The surface of an evaporated thin film of the ionic conductor β-PbF2 was analysed using X-ray photoelectron spectroscopy (XPS). The results were compared with those obtained from nuclear and secondary ion mass spectrometry measurements. An analysis of the Au-β-PbF2 interface shows the presence of a thin layer of partly oxidized metallic lead. Part of this interfacial lead diffused across the gold film towards the external surface where it became bound to oxygen. An electrical analysis of the interface was performed by studying the capacitance as a function of the surface potential. The differences between experimental and calculated values are discussed in the light of the XPS measurements.

A study of the metal-ionic conductor interface capacitances. II. Capacitance versus surface potential

Abstract Using the experimental method described in the preceding paper to determine the interface capacitances, the influence of surface potential value on these capacitances is analysed on thin film samples elaborated with gold as electrodes and lead fluoride as ionic conductor. The experimental capacitance-surface potential curve is compared to the theoretical curve calculated from Poissons equation and supposing a Boltzmann distribution of the ionic carriers. The results seem to show the presence of a saturation region obtained for negative values of the surface potential, and corresponding to a strong accumulation of fluorine vacancies.

A study of the metal-ionic conductor interface capacitances. I. Experimental method

Abstract In the study of interface capacitances of metal-ionic conductor contacts, difficulties are often encountered to make a reference electrode. The samples used in this work have two blocking electrodes and a third one, located in the bulk of the ionic material. This arrangement is elaborated by successive depositions of gold, lead fluoride, and gold thin films. Each interface capacitance can be obtained from a frequency analysis of the three-probe system. The results show that the structure is not symmetrical, because of differences in the roughness of the electrodes.

Influence d'une pression hydrostatique sur la conduction ionique de couches minces de PbF2

Abstract The conductivity of PbF 2 thin films was studied as a function of the hydrostatic pressure of a neutral gas at different temperatures. This conductivity varies with pressure according to an exponential law up to a value of about 4 kbar; the measured activation volume is 2.3 cm 3 mol -1 . The activation energy of the conductivity at these pressures remains unchanged in comparison with that found at atmospheric pressure, showing that the conduction mechanisms remain unchanged. For pressures above 4 kbar a fast rise in conductivity is attributed to a phase change accompanied by the creation of a large number of defects.