The electrical conductivity, σ, and thermoelectric power, S, of copper chromite (CuCr2O4) are reported in the temperature range 295 to 815 K A break (TB) in the slope of the plot of log σ against T−1 was observed around 556 K Apart from this break, the curves are linear, and their slopes correspond to activation energies of 060 eV (TB 556 K) A break (T′B) in the slope of the -S against T−1 plot was also observed round 556 K Apart from the break at this temperature, the S against T−1 curves are linear At T′B>556, S can be expressed by the relation 

$$S = - \left[ {\left( {\frac{{065 eV}}{{{\text{2}}eT}}} \right) + (042) mV K^{ - {\text{1}}} } \right]$$

The mechanism involved in the electrical transport is the hopping of holes from Cr4+ centres to neighbouring Cr3+ ions The typical hopping mobility of the holes is of the order of 106 m2 V−1 sec−1 The mobility activation energy of the holes in CuCr2O4 decreases with temperature due to the smoothing of the potential barriers between Cr4+ and Cr3+ sites

Electrical transport in copper chromite catalyst

Different coloured thallous tungstates were prepared by solid state reaction between thallous carbonate and tungsten trioxide at higher temperatures. The structure and thermal stability of different thallous tungstates were determined by powder X-ray diffraction and thermogravimetric analysis, respectively. The electrical conductivity (σ) and thermoelectric power (5) of pressed solid pellets of Tl2WO4 are reported in the temperature range 295 to 950 K. It is concluded that these materials have large numbers of oxygen ion vacancies and conduction occurs due to the electrons left by oxygen ions while escaping the solid. These electrons are trapped in the valence band and form centres analogous to a helium atom and electrical conductivity results when they enter the conduction band. The values of donor ionization energies have also been evaluated.

Structure, thermal stability and electrical transport in coloured thallous tungstates

Mesures de conductivite electrique et pouvoir thermoelectrique de Tl 2 MoO 4 entre 295 et 840 K: c'est un semiconducteur avec des porteurs de charge electroniques et des centres d'impurete comme centres donneurs

P. N. Ojha

Papers

Thermal stability of new rare earth thallates, MIIITIIIO3 (M=La, Nd)

Electrical transport in thallous molybdate