Investigation of thermoelectric properties of ZnV2O4 compound at high temperatures

In the present work, we report the experimental thermopower (α) data for ZnV₂O₄ in the high temperature range 300-600 K. The values of α are found to be  ∼184 and  ∼126 μV K^-1 at  ∼300 and  ∼600 K, respectively. The temperature dependent behavior of α is almost linear in the measured temperature range. In order to understand the large and positive α values observed in this compound, we have also investigated the electronic and thermoelectric properties by combining the ab initio electronic structure calculations with Boltzmann transport theory. Within the local spin density approximation plus Hubbard U, the anti-ferromagnetic ground state calculation gives an energy gap  ∼0.33 eV for U  =  3.7 eV, which is in accordance with the experimental results. The effective mass for holes in the valence band is found nearly four times that of electrons in the conduction band. The large effective mass of holes are mainly responsible for the observed positive and large α value in this compound. There is reasonably good matching between calculated and experimental α value in the temperature range 300-410 K. The power factor calculation shows that thermoelectric properties in the high temperature region can be enhanced by tuning the sample synthesis conditions and suitable doping. The estimated value of figure-of-merit, ZT, for p-type doped ZnV₂O₄ is  ∼0.3 in the temperature range 900-1400 K. It suggests that by an appropriate amount of p-type doping, this compound can be a good thermoelectric material in the high temperature region.