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-FexOy 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 Zn1-δFeδO solid solutions where 0.66 < δ < 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 Zn1-δFeδO) 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 by100–150% with doping due to growth of electron concentration. Some model concepts about scattering mechanisms and reasons of Seebeck effect enhancement have been developed.
Highlights
For many years 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
One application of ZnOFexOy powders with the weight relation (ZnO)-based composite ceramics is related to production of thermoelectric converters (TEC) [24,25]; this requires increasing electrical conductivity and reduction of materials thermal conductivity
After compacting at pressure of 6 GPa of ZnO and ZnOFexOy powders with the weight relation (ZnO)90(FexOy)10, the samples were subjected to the procedure of synthesis at 900 C for 2 h and to the grinding into powder again, compacting and annealing at 1200 C for 2 h in air
Summary
For many years 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 This forces to study correlations between structure and properties of composite ceramics, as well as striving for their cost-effective production technologies [1]. Such ceramic materials have a number of advantages compared with polycrystalline and epitaxial films, single crystals and other types of ZnO-based materials obtained using more expensive technologies. The aim of the work is to study the influence of structure, phase and chemical composition on electric and thermoelectric properties of ZnO-based ceramics when they are doped with iron using different types of FexOy (x 1⁄4 1, 2 and y 1⁄4 1, 2, 3) alloying agents
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