Conduction plane conductivity measurements

Electrical conductance The conductance measurements were made in a glass cell consisting ot two equivalent electrode sections. Circular platinized platinum electrodes parallel to the plane of the membrane were embedded in each section. The membrane area was 0.98 cm2. Resistance measurements were made with and without the membrane in O.IN NaCl solution. 

A coaxial probe can also be used to measure the through-plane conductivity of membranes. Figure 5.15 shows the schematic for a coaxial conductivity measurement cell. In this method, the membrane is cut to the same size as the inner conductor, and the measured resistance is the through-plane resistance. The resulting conductivity, 2.4 x 10 2 S/cm, is close to that reported in the literature. 

Tetrathieno[2,3- 3, 2 - 2",3"-/3", 2" - ]naphthalene 42 forms a 1 1 complex with tetracyano- -quinodimethane (TCNQ). X-Ray crystal structure determination of the complex confirms the molecular structure and reveals a onedimensional (1-D) structure with columns of alternating donor (D) and acceptor (A) moieties. The flat molecules stack on top of each other with a plane-to-plane D-A distance of 3.32(2) A. As a consequence of this structure, the material is fully insulating as confirmed by a compressed pellet conductivity measurement. 

Electrical conductivity measurements [41] along the i-axis and in the a-c plane reveal an extreme anisotropy single crystals after the currents had reached a steady value to avoid the effect of ionic... 

The orientation of cellulosic fibers has some effect on the conductivity of the paper. The conductivity in the XY plane of the sheet (surface conductivity parallel to most of the fibers) may be quite different from the conductivity along the Z direction (bulk conductivity perpendicular to the fibers). Comparison of surface and bulk conductivity for a given paper sheet can thus yield information which reflects the anisostropy in the structural morphology due to fiber orientation. Bulk conductivity measurements are also important since many paper sheets used in reprographic processes are composed of a conductive base sheet coated with a dielectric material 16. One important specification for these types of papers is the value of the bulk conductivity of the base paper. 

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. 

Early thermal-conductivity measurements on CVD diamond were performed on relatively thin films (less than 30 pm) with average lateral grain sizes of only a few micrometers, grown by MWP-CVD [71] or HF-CVD [72]. For both growth methods the in-plane thermal conductivity [ decreased from about 10 to less than 2Wcm K , if the methane concentration in the source gas was increased to several percent, accompanied by a deterioration of the film quality as to be judged from Raman spectra and (in the case of the HF-CVD samples) an increase of the H-content from 0.1 to 1.0%. 

Thermal conductivity measurements for parallel heat current and field lying in the hexagonal plane (Hiroi et al, 1997) have shown a dominating temperature dependence (r) and a linear behaviour k(T, //) // at low temperatures. This is again in agreement with the existence of node lines in A (k). However their exact position on the FS is not yet known. This has to be investigated by field-angle dependent thermal conductivity measurements which has been successM in this task in other unconventional superconductors as described in sect. 2. 

Illustration of in-plane conductivity measurement using the four-point probe technique. 

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