Conductivity measurements four-probe technique

In agreement with this analysis, single-crystal conductivity measurements using the four-probe technique reveals semiconducting behaviour for /r -(TMTTF)2Re04, as shown in Fig. 6.30. In this case aRj — 0.011 cm and Ea — 0.17 eV. 

Conductivity of (BN) iSO F and comparison with Cg SO F. In our early studies (12), a four-probe technique was employed, in which four platinum wires were used for electrical contact, and the samples were prepared by pressing powdered polycrystalline material into pellets. Because the platinum wires and the pellet surface are not ideally flat, a uniform intimate contact could not be assured between the wires and the pellet. The boundary effects due to the polycrystalline nature of the pellet sample also render such conductivity measurements unreliable. Attempts to use a contactless radio frequency inductive technique described by Zeller et al. (22) failed because this technique is not sensitive to low conductivities. A four-point probe measurement (21) on an intercalated highly oriented boron nitride sample was used in the present set of conductivity measurements. The <7295k 1.5Scm . The specific conductivity increased with decreasing temperature (see Fig. 1), it having nearly twice the room temperature value at 77 K. This indicates metallic behavior. 

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. 

Composites. The (CH)X/LDPE composites were prepared using the Ti(0Bu)4./Et3Al Ziegler-Natta catalyst system as previously described (10). The amount of (CH)X incorporated was determined by monitoring the acetylene uptake during the polymerization. Electrically conductive derivatives were prepared by immersion of the composites in a saturated 12/pentane solution for 24-48 hours. Electrical conductivities were measured by standard four-probe techniques. 

Measurements on d.c. conductivity were carried out by four-probe technique in the temperature range 77 to 350 K. 

FIGURE 2.1.18 Sheet conductivity o of the vacuum-gap rubrene single-crystal OFET, measured as a function of Vg at different T using the four-probe technique. (From Podzorov, V. et al., Phys. Rev. Lett., 93, 086602, 2004.)... 

The resistivity was then measured for PSSA-PVDF membranes with the four probe technique at room temperature under fully hydrated conditions to more accurately determine the conductivity of the samples, and compare these values to the those reported in the literature. The complex impedance plot of a representative sample of PSSA-PVDF is shown in Fig. 1.67, which corresponds to a conductivity value of 54 mS cm . The conductivity of Nafion 117... 

Fig. 1.115 Schematic of apparatus used in the "four probe technique of measuring the conductivity of membrane samples.

Conductivity measurements were carried out at room temperature using a four-probe technique in the helium filled drybox. Four platinum pressure contacts were made to the free-standing polyacetylene films. Electrical feedthroughs allowed equipment including a digital multimeter (Hewlett Packard 3468A) to be connected externally to the drybox. All measurements were made at least three times on several independent samples. 

In this part, the composition of T-CN nanocomposites was determined by FT-IR. Morphology of the nanocomposites was characterized by using SEM and transmission scanning electron microscope [TEM, JEOL JEM-2000EX). The conductivities of the nanocomposite films were measured by the four-probe technique (GZFTL RST-8) at room temperature using a semiconductor device analyzer. 

Compressed pellet electrical conductivity of DMTTTI was measured at room temperature using a four-probe technique. Electrical contacts were made with conductive silver paste (GC Electronics) using 1 micron gold wires. The room temperature conductivity is observed to be 1 x lo"" S/cm. This compares very well with that reported for TTTI. ... 

Electrical conductivities were calculated from the mean resistance values using the Van der Panw Equation (8.1) for the samples measured by the four-probe technique [1]. 

Figure 8.9 Photography of a sample used to measure the total conduction using the four probes technique.

CT complexes of 28b,c with TCNQ-F were successfully prepared. The ratio of the donor to TCNQ-F in the CT complexes is 1 1. The amounts of CT in the complexes were estimated to be 1.2 by comparison of the CN stretching shift. The electric conductivities of the compressed pellet of these CT complexes measured by the four-probe technique gave moderate electrical conductivities of o-jt = 3 X 10 S cm . Temperature dependence of their resistivity exhibited semiconducting properties, with activation energies of 0.10-0.13 eV. 

Fig. 11-3 Another variant of the four-probe technique for fiber conductivity measurement. After Wang et. al, [128], reproduced with permission.

Schematic diagram of electrodes used to measure the AC conductivity of P MX either by the two-probe or four-probe technique. The chemicai potentiais in the polymer electrolyte are not defined. 

To minimize the current flow through the sample, an ac four-point probe technique was used to monitor the conductivity of the sample with a lock-in amplifier (Stanford Research Systems, model SR 830 DSP). The lock-in amplifier enabled us to measure very low voltages without noise problems. 

The most common method for measuring the conductivity is the four-point probe technique [10]. Here a small current 1 is passed through the outer two probes and the voltage V is measured between the inner two probes (s is the distance between two probes). When such a measurement is performed with a semiconductor disk of diameter 2r and a thickness w, the resistivity is given by... 

The phase composition of the resulted specimens was identified by X-ray diffraction (XRD). Rod-like pieces (3x3xl5mm) and disk-shaped pieces (2mm thickness and 10mm diameter) were cut out for the electrical conductivity measurement and the thermal conductivity measurement, respectively. Microstmcture and phase distribution were observed by a scanning electron microscopy equipped with EPMA (JEOL JXA-8621MX). Electrical conductivity was measured using a D.C. four-probe method. Thermal conductivity was measured using a laser-flash technique. All the measurements were performed in the temperature range of 300 to 1200 K. 

The structure of Hg. BnAsFe can he described as octahedral AsFe" ions arranged on a lattice that contains linear nonintersecting channels in two mutually perpendicular directions. Within these channels are infinite chains of mercury atoms, each with a fractional formal charge of +0.35 and a mercury-mercury distance of 2.64(1) A. Conductivity experiments confirm the metallic nature of the compound. The resistivity, measured by a four-probe ac technique, decreases by a factor of 10 between room temperature and 4.2°K. No metal-insulator transition was detected. 

Early studies of electrochemically prepared PAn films used cyclic voltammetric techniques for the characterization of their electrochemical properties [16,145], Most of these studies addressed the chemical revesi-bility of the redox chemistry of the PAn films thus prepared and various forms of PAn were proposed to be involved in these redox chemistries [145], Depending on the oxidation state and whether or not it is protonatcd, PAn can be either an insulator or a conductor. The conductivities were measured in the dry state with mostly a four-probe method. Also, the molecular weight of electrochemically prepared PAn was found to be approximately 80000 [145b],... 

The room-temperature conductivities obtained for a number of PPy films appear in Table 12.3. We have applied both the linear four-probe and van der Pauw methods to the measurement of conductivity. The linear four-probe method has certain advantages the samples (narrow strips of film) are easily obtained and any anisotropy of the conductivity (within the film plane) can be investigated. The major source of error in conductivity measurements is the thickness measurement. The latter is conveniently done using a micrometer when the film thickness is greater than about 20 /zm. (Accurate thickness measurements of very thin films require the use of other techniques, such as electron microscopy.) It is advisable to make a number of conductivity measurements using specimens from different regions of a given film. 

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