Dependence Of Thermopower Research Articles

Thermopower in rare earth intermetallics

For transport phenomena such as electrical resistivity ϱ( T) or thermal resistivity W( T) the different scattering process contributions can simply be summed up to obtain the total value of ϱ or W. This is know as Mattiessen's rule. For the thermopower S( T) a more sophisticated method is necessary. Usually Kohler's rule or the Nordheim-Gorter rule is used to obtain the total value. Results from theoretical calculations for the temperature dependence of thermopower, which are based on a variational solution of the linearized Boltzmann equation, are used to discuss the different scattering contributions in case of thermopower. These results are used to analyze experimental data of thermopower for the isostructural compounds YAl 2 and GdAl 2. For two different heat-treated samples of the nonmagnetic YAl 2 compound, ϱ( T) and S( T) have been measured to separate the impurity and the phonon part of the total electron diffusion thermopower. From a comparison of S( T) for YAl 2 to those for the magnetic GdAl 2 the magnetic contribution has been estimated.

Composition dependence of thermopower and electrical resistivity in Cu-Co, Cu-Ni and Cu-Cd ferrospinels

The composition dependence of the electrical resistivity π and thermopower α was given for three systems of mixed ferrospinels (Cu x Co 1-x Fe 2O 4, Cu x Ni 1−x Fe 2O 4 and Cu x Cd 1−x Fe 2O 4, x varies from 0 to 1). Results show that there is a correlation between the composition dependence of the electrical properties and the intensity of magnetization. The mobility of charge carriers in these systems attain a maximum value at x = 0.5. For mixed inverse-normal Cu-Cd ferrospinels π, α and magnetization also reach maximum values for this composition. Comparison of the results with those for iron rich Zn-Fe and Ni-Fe ferrospinels showed that no correlation could be found in such case between the composition behaviour of magnetization and the electrical properties.

Composition dependence of thermopower and conductivity in Ni−Zn ferrites

The composition behaviour of the electrical resistivity ϱ, its activation energyEϱ and thermopower α is given for some samples of Ni−Zn ferrites prepared by the ceramic (s) and the co-precipitation (p) methods. Alloying with Zn ferrite leads to an increase of ϱ and α fors samples. For thep samples no observable change of ϱ and α was detected on alloying up to 60% of Zn ferrite. Calculated values of the drift mobilities for electrons at 400 K are of the order of 10−3 cm2/V s fors samples and 10−4 cm2/V s forp samples. Such values forμD favour a localized picture of electrons in these ferrites.