Abstract
The structure and electrical properties of (FexOy)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 Zn1−δFeδO with wurtzite structure and residual iron oxides FexOy, 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 Zn1−δFeδO. The temperature dependences of the electrical resistivity in the undoped ZnO in the temperature range of 6—300 K and in the doped ceramics (FexOy)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.
Highlights
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 Zn1−δFeδO
Summary
(ZnO)90(FeO)− ства монокристаллов, поликристал- 6 лических пленок, а также нано- 7. Нения (FexOy)10(ZnO), для которой масса порошков оксидов железа в исследуемых образцах соответствовала 10 % (вес.). В случае одноэтапного синтеза спрессованные таблетки спекали на воздухе при 1200 °С в течение 2 ч. Структуру и фазовый состав керамик исследовали при комнатной температуре методами рентгеновского дифракционного анализа (РДА) на автоматизированной установке ДРОН−3 М с использованием CuKα−излучения, и сканирующей электронной микроскопии (СЭМ) в режиме вторичных электронов на приборах LEO 1455VP Oxford Instruments и Tescan Vega 3LMU. Ток через образец задавался источником− измерителем Sub−Femtoamp Remote SourceMeter Keithley 6430, который позволял измерять электрическое сопротивление образцов в диапазоне 100 мкОм — 20 ГОм с точностью не хуже 0,1 %. Температуру образцов контролировали термодиодами LakeShore, калиброванными с точностью 0,0005 К и имеющими воспроизводимость 0,001 К, что позволяло стабилизировать и измерять температуру с точностью не хуже 0,005 К с помощью контроллера− измерителя LakeShore 331. Относительная погрешность измерения удельного электрического сопротивления не превышала 5 % и определялась, главным образом, неточностью измерения геометрических размеров образцов, а также размерами потенциальных электрических контактов
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