On manipulating the thermoelectric potential of p-type ZnO by nanostructuring

Abstract

Throughout this work, ZnO nanoparticles were produced by a simple co-precipitation method, in which the volume of the basic solution (NaOH, 5–30 ml) was varied to understand its effect on the properties of the nanoparticles. A structural and morphological effect was observed, namely a change in reflections between 2θ=31.75°(100) and 2θ=34.4°(002) peaks. At the same time, nanoparticles changed from a hexagonal prism shape to a desert-rose stones structure for high base concentrations. The transport measurements were performed from room temperature (RT) up to 340 K. At RT, a correlation between the Seebeck coefficient and the electrical conductivity was achieved, whereas the thermal conductivity behaves distinctly. A thermal conductivity value of 0.5 W m-1 K−1 was observed, which is two orders of magnitude lower than the bulk counterpart. The behaviours of the PF and ZT also reveal the different influences of the electrons and the phonons for the different nanostructures, since the electronic phenomena predominate in the hexagonal prism structures, the phonon phenomena predominate in the desert-rose stones, due to the reduced dimension of these structures. For higher temperatures, a thermal activation model was used to determine the Activation Energy (Ea), leading to values in the hundredths of meV range, with higher values for the volumes of NaOH where a mixture of the two types of structures is observed, where the presence of different interfaces created a barrier for the carriers to pass from grain to grain.