Percolation phenomena were studied in a series of six composites with a cellular structure. Measurements made on the composites include dc and ac electrical conductivity, dielectric constant, 1/for flicker noise and magnetoresistance. Results arising from these extensive measurements were fitted to the percolation power laws and a phenomenological equation to give various exponents, which are presented, discussed and compared.

Abstract. We report measurements of the surface topography of a 70 nm gold film deposited on mica preheated to 300 oC in UHV performed with a Scanning Tunneling Microscope (STM). From these measurements we determine the rms roughness amplitude and the lateral correlation length characterizing the average height-height autocorrelation function on a nanometric scale.We also report a method of analyzing thin film resistivity data that departs sharply from the traditional method of parameter fitting. This method allows the determination of the resistivity and mean free path characterizing the bulk from the measured thin film resistivity by means of a new iteration procedure, that uses as input data the roughness parameters experimentally determined with the STM and any of the available quantum transport theories, without adjustable parameters. We examine the resistivity data reported by Sambles et al. [Philos. Trans. R. Soc. London, Ser. A304, 365 (1982)] for gold films deposited on mica under similar substrate temperature and similar speed of evaporation. The remarkable outcome is that any of the quantum transport theories available, describe approximately both the temperature as well as the thickness dependence of the resistivity data without any adjustable parameter. Another surprise is that the parameters characterizing the bulk—assumed to be independent of thickness for many years—turn out to be thickness dependent.

We report the electronic characterization of n-ScN in ScN-Si heterojunctions using Deep Level Transient Spectroscopy of electrically active deep levels. ScN material was grown by plasma assisted physical vapor deposition and by reactive sputtering on commercial p+ Si substrates. Deep level transient spectroscopy of the junction grown by plasma assisted physical vapor deposition shows the presence of an electronic trap with activation energy EC-ET= 0.51 eV. The trap has a higher concentration (1.2–1.6 1013cm−3) closer to the ScN/Si interface. Junctions grown by sputtering also have an electronic trap, situated at about EC-ET= 0.90 eV.

Mixed ionic-electronic conductors (MIECs) which have both ionic and electronic species as charge carriers have a wide range of applications, such as electrodes in fuel cells, electrocatalytic reactors, and gas separating membranes. They may have either electronic or ionic species as the majority charge carriers. In addition to the single-phase mixed conductors, they may be fabricated by mixing two different phases of materials. Although these composites have been less studied than the single phase MIECs, the combined properties are often superior to single phase MIECs, and properties not seen in an individual phase may appear in the composite phase.

YSZ-based composite systems were chosen to test the effect of transition-metal-oxide (TMO) addition on the electronic conductivity of composite. To induce mixed conductivity, electronic-conducting TMOs such as NiO and Mn2O3 were added into YSZ above the solubility limit. While the solid solubility of NiO in YSZ is limited that of Mn2O3 is large.

In this work, mixed conducting yttria (8 mol%) stabilized zirconia (YSZ) - TMO composites were prepared in full composition range and the electrical conductivity of the composites was measured by 4-probe d.c. conductivity. Electromotive force (emf) measurements of the galvanic cell, current-voltage (I-V) measurements in ion blocking condition and the oxygen-partial-pressure dependent conductivity have been used to determine the contribution of the ionic and electronic charge carriers on the conductivity. Thus the composition-dependent electrical properties were used to explain the percolation behavior of electronic charge carriers in ionic matrix.

Although the total conductivity of dense YSZ-TMO composite was variable with TMO content, the partial-electronic conductivity increased and the ionic conductivity decreased. The composition-dependent conductivity was discussed.

Polymer based composites are very attractive materials for a plurality of technical applications. For electrical purposes the resistivity of such materials can be tuned over many orders of magnitude from highly insulating (1014&cm) to well conducting (10-3&cm) states. One particular class of polymer based composites even show a strong non-linear reversible change in resistivity with temperature between conduction and insulation. Such a pronounced effect of positive temperature coefficient of resistivity (PTCR) can be technically used, for example, in self regulating heating devices, for temperature sensing or, as a very challenging and important task, for current (i.e. over- as well as short-circuit currents) limiting and interrupting devices. The PTCR-devices act similar like fuses but repetitively, which offers technical and economical benefits.

In the present work we investigate how the physical properties of the conducting filler influence the switching characteristics of the PTC material. Experimental results on resistivity and its change under active heating by Joule's losses during current flow are presented and discussed for different composites, compounded with fillers like carbon black, Ni/Ag, TiB2 or WC/Co. The strong resistance change caused by break-off and separation of particle-particle micro-contacts is driven by the very different thermal expansion coefficients of filler and matrix. It is in particular demonstrated how the heat capacity of filler-particles influences the dynamics of the micro-contact separation.

The microstructure and damage of the interlaminar interface of continuous carbon fiber polymer-matrix structural composites were monitored during dynamic changes in temperature, humidity and stress by contact electrical resistivity measurement. The stress was compressive, in the direction perpendicular to the interface. Temperature, humidity and stress had reversible effects on the resistivity, due to the effects on the interfacial microstructure, such as the extent of contact between fibers of adjacent laminae. These parameters had irreversible effects on the resistivity, due to relaxation and damage of the interface. The effects differed between composites with thermoplastic and thermoset matrices. The reversible effects allow the use of the contact resistivity as an indicator of temperature, humidity and stress.

This paper discusses how inhomogeneities and heterogeneities enter impedance and conductivity analyses in the case of microstructural periodicity. The specific considerations of various examples of ionically and ionically/electronically conductiong materials systems (bicrystals, microcrystalline and nanocrystalline samples) show how a reliable and thorough characterization is possible.