Electron transport and thermoelectric properties of ZnO ceramics doped with Fe

Abstract

Currently, special attention is paid to the search for new ceramic materials based on wide-gap oxides, as well as to the study of their structure and properties with a view to their application in various areas of electronic and optoelectronic industry. Conventional double-step ceramic technology has been used to obtain samples in this experiment. After compacting at the pressure of 6 GPa of ZnO and ZnO-Fe x O y powders in different weight relations, the samples were subjected to the procedure of synthesis at 1173 K for 2 h and then to the annealing at 1473 K for 3 h on air. The samples structure was investigated by the Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD) and Raman spectroscopy methods. Temperature dependences of resistivity, magnetoresistance, Hall and Seebeck effects were experimentally studied in the range from 4 to 700 K. As the experiments have shown, the size of grains in the obtained ceramic samples after synthesis was in submicron range. An XRD study showed the saving of the wurtzite structure in Zn 1- d Fe d O solid solutions where 0.66 < d < 0.81 at. % regardless of the type of the doping agent. At the same time, the replacement of zinc by iron atoms led to the contraction of the ZnO lattice. All the samples studied (ZnO and Zn 1- d Fe d O) demonstrate n-type conductivity. The temperature dependencies of resistivity have shown two specific features: the presence of energy level about 0.35 eV below the conduction band bottom for the doped ceramic samples (unknown in literature) and conductance with the changing activation energy at temperatures below 200 K for the undoped ZnO ceramic samples. Seebeck coefficient increased by100e150% with doping due to growth of electron concentration. Some model concepts about scattering mechanisms and reasons of Seebeck effect enhancement have been developed.