Bulk resistivity measurements technique

Conventional two-electrode dc measurements on ceramics only yield conductivities that are averaged over contributions of bulk, grain boundaries and electrodes. Experimental techniques are therefore required to split the total sample resistance Rtot into its individual contributions. Four-point dc measurements using different electrodes for current supply and voltage measurement can, for example, be applied to avoid the influence of electrode resistances. In 1969 Bauerle [197] showed that impedance spectroscopy (i.e. frequency-dependent ac resistance measurements) facilitates a differentiation between bulk, grain boundary and electrode resistances in doped ZrC>2 samples. Since that time, this technique has become common in the field of solid state ionics and today it is probably the most important tool for investigating electrical transport in and electrochemical properties of ionic solids. Impedance spectroscopy is also widely used in liquid electrochemistry and reviews on this technique be found in Refs. [198 201], In this section, just some basic aspects of impedance spectroscopic studies in solid state ionics are discussed. 

The selection of the thermal management materials for electronic packaging purposes demands close examination of thermophysical characteristics, such as thermal conductivity and diffusivity, specific heat capacity, coefficient of thermal expansion, and thermal shock resistance. A variety of measurement techniques have been developed to evaluate these properties, but this chapter focuses on thermal conductivity and diffusivity evaluation methods. Each of them is suitable for a limited range of materials, depending on the thermal properties and the medium temperature. The precise determination of the thermal properties of bulk composite materials is challenging. For instance, loss terms for the heat input intended to flow through the sample usually exist and can be difficult to quantify. 

The most commonly used method for resistance measurements, instead, is the four-point probe technique (Valdes, 1954 Uhlir, 1955 Schroeder, 1998), which is a standard characterization method in semiconductor and display industry (metals ASTM, 1996a TCO ASTM, 2(X)2b) both for bulk materials and thin films. This universal and absolute technique uses four separate electrodes to allow an almost current-less voltage... 

Hardness is a measurement of material resistance to plastic deformation in most cases. It is a simple nondestructive technique to test material indentation resistance, scratch resistance, wear resistance, or machinability. Hardness testing can be conducted by various methods, and it has long been used in analyzing part mechanical properties. In reverse engineering, this test is also widely used to check the material heat treatment condition and strength, particularly for a noncritical part, to save costs. The hardness of a material is usually quantitatively represented by a hardness number in various scales. The most utilized scales are Brinell, Rockwell, and Vickers for bulk hardness measurements. Knoop, Vickers microhardness, and other microhardness scales are used for very small area hardness measurements. Rockwell superficial and Shore scleroscope tests are used for surface hardness measurements. Surface hardness can also be measured on a nanoscale today. 

Diamond Hints, although not approaching bulk diamond, are harder than most refractory nitride and carbide thin films, which makes them attractive for tribological coatings. Transparency in the visible and infrared regions of the optical spectrum can be maintained and index-of-refraction values approaching that of bulk diamond have been measured. Electrical resistivities of diamond films have been produced within the full range of bulk diamond, and thermal conductivities equivalent to those of bulk diamond also have been achieved. As substrates for semiconductor electronic devices, diamond films can be produced by both the PACVD and IBRD techniques. 

Manipulation of the A, FT, and />, values in Eq. (11) will naturally produce different values of B. Accordingly, if it is desirable that B be as low as possible, this may be accomplished in one of three ways (1) reducing the bioburden A of the bulk product, (2) increasing the equivalent exposure time FT, or (3) employing a micro-organism with a lower D value at the specified temperature. Since option 3 most likely is impossible, as the most resistant micro-organisms of a fixed D value must be used in sterilizer validation, one must either employ techniques to assure the lowest possible measurable microbial bioburden prior to sterilization or simply increase the sterilization cycle time. 

Other common means for determining the direct d33 coefficients of bulk samples include Berlincourtstyle approaches. Berlincourt meters are available commercially from several sources. In most cases, the sample to be measured is mechanically clamped between jaws with pressures on the order of a few N. The charge output due to a small mechanical oscillation (forces 0.1-0.3N) is then determined. It is important to note that this technique is appropriate for measurements of bulk samples with stable domain states, only. Measurement accuracy is also better when highly resistive samples are used. 

For the characterization of the polysiloxane membranes we have measured the impedance spectra in the presence of different concentrations of cations. Both valinomycin (1) and the two different hemispherands (2 and 3) have been incorporated in these membranes. Buck et al (24, 25) have shown that this technique allows to separate the surface exchange rates and the rates of bulk transport. The copolymer described above containing valinomycin initially has a very high resistance but after several days conditioning in a 0.1 M KC1 solution the resistance is the same as that of a similar membrane to which KB(4-C1C6H4)4 was added. 

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