Hall voltage conduction

Due to the symmetrical construction the resulting magnetic field between the two coils is zero in y-direction, if a conductive structure is symmetrically situated in the area a (see fig. 3) in the near of the probe. A resulting field is detectable by the Hall-effect device, if there are unsym-metrics in the structure in area a. The value of the Hall voltage is proportional to the detected magnetic field. 

This same equation is, of course, also used to rationalise the general electronic behaviour of metals, semiconductors and insulators. The quantitative application of Eqn (2.1) is handicapped for ionic conductors by the great difficulty in obtaining independent estimates of c,- and u,-. Hall effect measurements can be used with electronic conductors to provide a means of separating c, and u,- but the Hall voltages associated with ionic conduction are at the nanovolt level and are generally too small to measure with any confidence. Furthermore, the validity of Hall measurements on hopping conductors is in doubt. 

Morrison (31) has compared measurements of the Hall effect and of the resistance. The Hall voltage is inversely proportional to the average concentration of carriers in the material (24), and so, for zinc oxide, will be inversely proportional to the concentration of carriers in the large grains (Fig. 2) of the material. Figure 3 shows an example in which the resistance and the inverse of the Hall voltage measured on a sintered sample of zinc oxide are plotted as functions of the time. This illustrates that the number of carriers in the bulk of the sample may remain relatively constant, while the conductance varies widely, all at constant temperature. 

Morrison (31), using sintered zinc oxide, applied a different technique to study the conductivity effects in the range between room temperature and 500°C. He studied the variation in conductance as a function of time with the temperature held constant. Figure 3 shows one such conductivity-time experiment. The sample used was a slab of zinc oxide cut from a pill which had been compressed and sintered in air for eighteen hours at 1000°C. The sample was immersed in oil (the oil does not penetrate into the pores of the sample) at the start of the run. The sample container was immersed in boiling water, the temperature reaching 100 C in the order of one-half of a minute. The conductance was recorded as a function of time while the sample was held at 100°C. The results are shown in Fig. 3. The inverse of the Hall voltage is also plotted as a function of time. An interpretation of the Hall measurement is discussed in Section III. 

From Fig. 3 it is evident, upon comparison with the Hall voltage, that the reversible time dependence of the conductance is also associated with... 

The final transport measurement to be considered is the Hall effect. This is the most intriguing transport property, but has been so difiicult to imderstand that it has not contributed much towards the elucidation of the conduction mechanisms. The reason is that the Hall effect is anomalous and has the opposite sign from that which is normally expected. Thus holes give a negative Hall voltage and... 

Later on. Song et al. [19] performed a four-point resistivity measurement on a large bundle of CNTs of 60 pm diameter and 350 pm distance between the two voltage probes. They interpreted their resistivity, magnetoresistanee and Hall effect results in terms of semimetallie conduction and 2D weak localisation as for the case of disordered turbostratie graphite. 

Electrical conductivity (a.c. and d.c.), Hall measurements, and determination of Seebeck voltage. 

The electrical conductivity(<, carrier concentration(n) and Hall mobility(/i ) were measured at 300 Kfor the p and n-type sintered PbTe. The characterization of the p-n jimction was conducted at 300 K by measuring thermoelectromotive force within temperature difference of 5 K, and voltage (electric potential) distribution using 4-probe method and current(])-voltage(V) relationship in forward and reverse bias. 

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