Electrical conductivity Four-probe technique

The cesium [hydrogen bis(sulfate)] tetracyanoplatinate complex exhibits a room-temperature electrical conductivity (four probe technique) of approximately 113 ohms 1 cm 1, while that of the Rb analog (Pt—Pt - 2.83 A) is 1500-2000 ohms"1 cm 1. 

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. 

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. 

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]. 

For the total electrical conductivity obtained by the four-probes technique, a narrow plateau regime due to ionic conduction and a slope of approximately —1/6 due to n-type conduction were observed imder high and low partial oxygen pressure regions, respectively. The total electrical conductivity was then fitted by the following equation ... 

The electrical conductivities of the different PANi/DBSA complexes prepared under various conditions of complexation were investigated by the four-probe technique for pressed pellets of the green-black complexes. As the amount of dopant increases, the conductivities of the resulting complexes (100°C, 20 min) increase at the beginning (from 0.1 S/cm) by almost two orders of magnitude (10 S/cm), reach a maximum at PANi DBSA = 1 3, and then decrease to 1-3 S/cn. 

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. 

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 electrical conductivity of a pressed pellet sample was measured as a function of temperature using a four-probe ac technique. A ca. 2 X 3 X 1 mm sample was cut from a cold-pressed pellet of the... 

Mglu204 thin films were prepared by the spray pyrolysis technique and H+, Li+ ions were implanted at room temperature. The acceleration energy was 1.5 MeV and the fluence range studied spanned from 10 to 10 ions cm . Some of the implanted films were annealed at 450°C for 5 h. Electrical conductivity measurements were carried out using a four-probe method and Hall measurements were performed by the Van der Pauw method under the magnetic field of 5000 Gauss (0.5 T). 

Kim] DC four probe and laser flash techniques Thermoelectric power, electrical and thermal conductivity... 

Fibre formation and morphology of the coated nanofibres can be determined using SEM. A small section of the produced web can be placed on a SEM sample holder and should be coated with gold. Electrical conductivity of the coated mats can then be determined by employing the standard four-point probe technique. 

Typically, electrical conductivity of EAPs is measured in units of S/cm. Both two- and four-point probe techniques are used to measure a in films and pressed pellets (255). Conductivities as high as 10 S/cm have been reported for several EAPs. Values vary depending on synthetic procedures, fabrication techniques, and measurement methods. EAPs are typically only partially crystalline (256-258) amorphous EAPs have been reported (259-261). Therefore, disorder plays a significant role in their electrical conductivities, and the conductivity arises from the metal-insulator transition (262). As an example, PA with the highest conductivity reported so far shows temperature dependence of conductivity (263). Thus, electrical conductivity is limited by the disorder-induced localization of the electrons rather than by the intrinsic conductivity of the delocalized charges on the polymer backbone. Table 2 shows conductivities for several well-known EAPs (26-28). 

As well as the above techniques, dry electrical conductivity measurements using the four-point probe technique may be useful. However, it is important to remember that this is likely to be much different from solution conductivity. 

Surface conductivity of glass or of thin films on glass is often measured in terms of sheet resistance (ohms per square, or Q/D) using a four-point probe technique. Electrically contacting point probes are placed at the four comers of a square on the surface or the fihn. A current I is allowed to pass through two adjacent probes, and the potential difference V developed across the other two probes is measured. Sheet resistance in this arrangement is calculated as... 

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