Measurements of anisotropy, thermoelectric behaviour andmulti-fractal aspects of FeSi and of complex custom made TE materials


M.Kuramitsu1,2, J. M. Redondo1, G. Noriega2


1Departamentde Física Aplicada, B5 Campus Nord, Univ. Politécnica deCatalunya, Barcelona 08034, Spain

2CIDETE,C/. Anselmo Clave, Vilanova i la Geltru, Barcelona 08800, Spain


The understanding of the strongly directionalproperties of certain thermoelectric materials needs further understanding ofthe subtle carrier and thermal electron paths that take place in complexnatural and custom made materials. The way in which the material structure isbuilt sometimes leads to strong anisotropy in basic properties such as theSeebeck coefficient measured at a very small scale. A custom developed program(Grau, 2003) that calculates multifractal relationships using advanced imageanalysis aspects, was used at the same time as other techniques were used.

The power relationships between the differentconcentration isolines (Redondo et al., 1986) in a 2D section of the materialperpendicular to the two orthogonal axes where the Voltage as a function oftemperature were measured, and its variation with both range of scales andtemperature may be used to explain the 30% differences measured in the Seebeckcoefficients. The ratio between the surface separating subsets of differentmaterial properties and the volumes of the respective grains may be related to changesin fluxes that may be very different when measured at different scales inanisotropic and non-homogeneous materials (Linden and Redondo, 2001).

Basic topological and physical properties taredefined in a different way, when geometrical self similarity is apparent for alarge range of scales studied in terms of box-counting fractal algorithms (Redondo 1990) and the relationshipbetween  some basic Thermo-electriceffects and geometry are studied.

Thanks are due to J. Grau and I.R.Cantalapiedra for help with the multifractal Imacalc Programme, the initialexperiments and optical devices. CIDETE and The European Union Project  NANOTHERMEL provided some of the custommade thermoelectric materials used in the experiments.

Redondo (1990) PhD Thesis, DAMTP, Univ. of Cambridge.

Redondo J.M. and Garriga J.N. (1986), CIMNE vol MGF,343-352.

Linden P.F. and Redondo J.M. (2001) CIMNE. Barcelona.

Grau J. (2003) Annex. PhD. Thesis