THERMAL-DIFFUSION IN CRYSTALLINE BINARY COMPOUNDS WITH NARROW RANGE OF HOMOGENEITY .1. A NEW EXPERIMENT FOR THE DETERMINATION OF THE HEAT OF TRANSPORT

The formal analysis of the coupling between diffusional matter and hea t transport shows that diffusional matter fluxes are driven by both te mperature and composition gradients, and that matter fluxes are always connected with heat fluxes. An important concept in the description o f this coupling is the introduction of so-called heats of transport. T he heals of transport, being combinations of phenomenological transpor t coefficients, denote the relation between individual matter fluxes a nd related heat fluxes for isothermal systems. For the case of mixed i onic/electronic conducting binary compounds with narrow ranges of homo geneity, A(1+delta)X(nu), a new experiment for the determination of th e reduced heat of transport of metal A is proposed and discussed with respect to a possible realization. The experiment is based on the dire ct measurement of the flux of the metal component in a temperature gra dient, under special boundary conditions for the composition of the sa mple, and gives direct access to the (reduced) heat of transport, Q(A) . Alternative ways for the determination of the heat of transport are summarized and compared with the proposed experiment.