Electrical resistance, four-probe method

Samples were characterized by X-ray diffraction, magnetic susceptibility and chemical analysis with some results summarized in Table 1. The electrical resistivity measurements were made down to 80 K using a four-probe method. Raman scattering experiments used the excitation line A = 514.5 nm of an Ar+ laser in a quasi-backscattering geometry. The laser power of 5 mW was focused to a 0.1 mm diameter spot on the (010) surface. The averaged laser power density amounts to 6 105 W/m2 which is much less compared to earlier Raman studies in manganites [12-15],... 

The Rb based on the sample cannot be calculated correctly, since the electric charge transfer resistance and the electric double layer in an electrode interface are also detected as a resistance, even if bias voltage is impressed to the measurement cell in order to measure the ionic conductivity. For the ionic conductivity measurement, a dc four-probe method, or the complex-impedance method, is used to separate sample bulk and electrode interface [4]. In particular, the complex-impedance method has the advantage that it can be performed with both nonblocking electrodes (the same element for carrier ion and metal M) and blocking electrodes (usually platinum and stainless steel were used where charge cannot be transferred between the electrode and carrier ions). The two-probe cell, where the sample is sandwiched between two pohshed and washed parallel flat electrodes, is used in the ionic conductivity measurement by complex-impedance method as shown in Figure 6.1. 

X-ray residual stress determination was performed on the surface of the samples prepared by HIP sintering. The measured residual stress was compared with the results calculated by the finite element method (FEM). The electrical resistivity was measured by the four probes method on the slices cut from the cylinder samples. In order to inspect the thermal stability, the samples were annealed at 900 °C for 24 hour in vacuum. The microstructure on the section was observed by scanning electron microscope. 

Electrical resistivity measurement adopted conventional four probes method. Seebeck coefficient was measured by the standard DC method. Thermal conductivity k was calculated from density, specific heat, and thermal diffiisivity. Specific heat measurement was carried out by use of a differential scanning calorimeter (DSC model 8230, Rigaku, Japan) compared with a standard material of a -AI2O3. The values of thermal diffiisivity obtained from a differential phase analysis of photo-pyroelectric signal (AL- A 0 analysis) [9]. All measiu ements were done at room temperature. 

Electrical Resistivity. The electrical resistivity of these materials was measured from room temperature to 15 K at 5 K intervals on bars, 6-10 mm long and 1 mm square, using a DC four-probe method. The electrical contacts were made with fine platinum wire and silver paste. A constant current of <10 mA was used. The voltage difference was measured to 0.1 fiV. The temperature of the specimen was maintained by a closed-cycle cryogenic system and measured using a calibrated silicon diode. 

The electrical conductivities were measured using a standard four-probe method to minimize the surface contact resistance. 

Many polymers and most PMC show no or only comparatively low electrical conductivity, which limits application of electromagnetic test methods. One of the main exceptions is CFRP. The continuous network of carbon fibers in CFRP allows for electrical resistance measurements, eg, based on the four-probe method. Electrical potential (101) or resistance methods are used in fracture mechanics to detect delaminations (102) and to monitor damage in CFRP (103). Whether the application of electrodes is nondestructive depends on the intended use. 

Electrical conductivity is used for the calculation of melt flow under a magnetic field Electrical conductivity is also used to estimate thermal conductivity assuming the Wiedemann-Franz law, as shown in Eq. (4.2). Glazov et al. [5], Schnyders and Zytveld [52], and Sasaki et al. [8] measured electrical conductivity using a four-probe method. Figure 4.22 shows a typical measurement cell for the four-probe method, where resistivity, which is the inverse of electrical conductivity, is measured [8j. 

The most typical way to measure the in-plane electrical conductivity of a diffusion layer is through the use of the four-point probe method. A small current is applied across the sample material a separate set of voltage measuring probes that are in touch with the material are used to measure the resulting voltage drop in order to calculate the resistance. With these values, the in-plane resistivity, p, can be calculated with the following equation [9,233] ... 

The resistivity of a free-standing bulk sample was measured by depositing Pt electrodes by FIB and by employing the four point probe method [8], The resistivity of the bulk was 10 - 15 Q cm. The carrier concentration was estimated to be less than 1016 cm 3 by the plasmon-coupled mode in the Raman spectrum. These electrical measurements show that the crystal is of relatively high purity. 

Electrical resistivity was measured by a d.c. method using four-probe techniques to avoid problems arising from contact resistance. Pressure contacts were used for both current and potential probes. At low temperatures, the current contacts could be improved by ultrasonically tinning the ends of the samples. 

To measure the Seebeck coefficient a, heat was applied to the sample which was placed between the two Cu discs. The thermoelectric electromotive force (E) was measured upon applying small temperature difference (JT <2 E) between the both ends of the sample. The Seebeck coefficient a of the compound was determined from the E/JT. The electrical resistivity p of the compound was measured by the four-probe technique. The repeat measurement was made rapidly with a duration smaller than one second to prevent errors due to the Peltier effect [3]. The thermal conductivity k was measured by the static comparative method [3] using a transparent Si02 ( k =1.36 W/Km at room temperature) as a standard sample in 5x10 torr. 

The electrical resistivity and the Seebeck coefficient of the specimens were measured up to 800 C. To localize the boundary between the portions of graded doping, the distribution of electrical resistivities around the boundary was investigated by the four-terminal method in which one end of voltage probes was scanned automatedly. 

This article has addressed a number of issues relating to the electrical properties of paper or fibrous structures. It was shown that reliable measurement methods are now available for estimating both the bulk and surface conductivities of paper. In the case of the bulk conductivity, a new in situ pressure conductivity cell was described which significantlyreduces contact resistance. The surface conductivity can be determined by the application of a modified four-point probe method first used on paper by Cronch<15). It was shown that the degree of refining has a small effect on the bulk conductivity of paper. 

Resistivity Measurements. Four-probe resistivity measurements were also used to determine critical temperatures. The resistance vs. temperature profile for the crystal shown in Fig. 4 gives a critical temperature of about 85 K. Electrical contact was made to the crystal by wire-bonding aluminum to the surface however, this method is not always successful. Alternative techniques have given ohmic contacts with low resistance which have eliminated the self-heating problem associated with the aforementioned method. These results will be the subject of another publication. 

Specimens were strained in a push-pull mode by an Instron machine, Model TF-DM, which has cross head speeds from 0.05 to 0,5 cm/min and a load capability up to 10" kg. Details of the apparatus for the mechanical and electrical tests are reported elsewhere Only a brief description of the electrical portion is given here. The resistivity was measured by the typical four-probe dc method. A set of voltage leads were soft-soldered across the gauge length of the specimen surface. 

IV. Keithley electrometer to measure the electrical resistances of pure polymers and their blends cast films (thickness of each sample, 6.0 pm) on microscope slides (6.25 cm X 0.1 cm), based on the two-probe method [1] and four-probe Van der Pauw technique [1-2]. 

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