Impedance response and modeling of composites containing aligned semiconductor whiskers: Effects of dc-bias partitioning and percolated-cluster length, topology, and filler interfaces

Abstract

Impedance spectroscopy and modeling were used to investigate the partitioning of 0-40 V dc bias in composites containing alumina and different volume fractions of silicon carbide whiskers (SiCw), which formed low-connectivity percolated clusters. Differences in response between long (∼25 cm) composite rods and thin (∼1.7 mm) slices thereof were interpreted in terms of the relative contributions to the impedance from the electrodes and SiCw-percolated clusters of the composite samples. Bias had minimal effect on the impedance of rods, because its distribution across the long percolated clusters within translated to low electric fields at the SiCw-SiCw interfaces. The impedance of thin slices was more sensitive to bias and was mainly due to such interfaces. The associated dc resistance and effective capacitance decreased significantly with increasing dc bias. A model for symmetrical Schottky energy barriers at interfaces fit the capacitance trend and outputted a parameter Φi/κ¯i. Different models for the non-linear current-voltage behavior were related to each other and indicated weak varistor-like behavior, i.e., 1.15 ≤ αV ≤ 2.57. With increasing SiCw content and composite dc conductivity, Φi/κ¯i increased and the varistor non-linearity strength αV decreased. Also, the exponent t describing conductivity divergence at percolation was reduced at large dc bias. A new model of percolated clusters was proposed and correctly predicted the qualitative character and some quantitative aspects of these experimental results. The model is based on tendencies of the current distribution, which are expected from the topological structure and contrast between interface/whisker electrical behavior. Accordingly, it outputs the voltage-distribution tendencies.

The effect of substrate pore size on the network interconnectivity and electrical properties of dropcasted multiwalled carbon nanotube thin films

“…It should be added that the quality of contact between individual conducting fillers has also previously been detected by impedance measurements in both polymer and ceramic composites containing conducting fillers that form percolating networks. 26,27 C 1 (the capacitance of the bundles) and C 2 (the capacitance of the junctions) describe the amount of charge capable of being stored in the CNT networks. In all cases, the capacitance for the bundles is higher than that for the junctions.…”

Detection of Different Interfaces in Percolated Networks of Antimony Tin Oxide: Borosilicate Glass Composites by Impedance Spectroscopy

“…Both the temperature and pressure dictated the compaction of the ATO, which as a result, influenced the contact between ATO particles. The type and extent of contact between particles is referred to as quality of contact, and depending on this quality of contact the electrical properties can vary . This has been observed in other insulator–conductor composites depending on the method of processing …”

Assessment of Homogeneity of Extruded Alumina-SiC Composite Rods Used in Microwave Heating Applications by Impedance Spectroscopy

“…Similarly in the thin slices, 5V DC bias was sufficient to eliminate the low frequency electrode semicircle while having minimal impact on the bulk response. 5 Increasing the voltage also had a secondary effect of shrinking the high frequency bulk semicircle in the thin slices. This was suggested to be caused by the non-linear response at the SiC w-SiC w interfaces in the percolated SiC w clusters.…”

“…This was suggested to be caused by the non-linear response at the SiC w-SiC w interfaces in the percolated SiC w clusters. 5 A model that takes into account the quality 657 of the contacts between individual whiskers and the network they form has been compared to river geography. 5 The purpose of this study was to conduct a more detailed study of long rods, and different thickness sections cut from them to try to understand what led to the differences observed.…”

“…[1][2][3][4][5] Silicon carbide whiskers are 0.5 μm in diameter and can have aspect ratios as high as 20. The different processing methods therefore result in different whisker alignment, and consequently they have different electrical responses.…”