Structure and electric properties of zink oxide−based ceramics doped with iron

Abstract

The structure and electrical properties of (Fe_xO_y)₁₀ (ZnO)₉₀ ceramics (0 ≤ x ≤ 3; 1 ≤ y ≤ 4) synthesized in air by one− and two−stage method were studied. To dope ZnO, powders of FeO, α−Fe₂O₃, and Fe₃O₄ or a mixture (α−Fe₂O₃ + FeO) were used. On the basis of X−ray diffraction analysis, gamma−resonance spectroscopy and Raman spectroscopy, it was established that at fixed average iron concentrations of 1—3 at.% in ceramic samples, at least three phases are formed: solid solution Zn_1−δFe_δO with wurtzite structure and residual iron oxides Fe_xO_y, used as doping agents. Scanning electron microscopy and energy−dispersive X−ray analysis have shown that, in the studied ceramics, the grain sizes of the wurtzite phase decreased from several tens of micrometers using one−step synthesis to the submicron level for the case of two−step synthesis. It was found that the incorporation of iron into ZnO leads to a contraction of the crystal lattice in the wurtzite phase and the stronger, the higher the proportion of oxygen in the doping iron oxides FexOy. The study of the temperature dependences of the electrical resistivity have shown that deep donor centers with an activation energy of about 0.35 eV are formed in the wurtzite phase Zn_1−δFe_δO. The temperature dependences of the electrical resistivity in the undoped ZnO in the temperature range of 6—300 K and in the doped ceramics (Fe_xO_y)₁₀(ZnO)₉₀, obtained by the one−step synthesis method, at temperatures below 50 K, are characterized by a variable activation energy, which indicates a strong disordering of their structure.