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I. P. BYKOV, A. B. BRIK, V. V. BEVZ, T. E. KONSTANTINOVA, and I. A. YASHCHISHIN
«Radiospectroscopy Investigations of Zirconia Nanosized Powders»
PACS numbers: 71.70.Jp, 73.20.Mf, 73.22.Lp, 76.30.-v, 77.84.Bw, 81.05.Je, 81.07.Wx
Electron paramagnetic resonance and proton magnetic resonance are used for investigation of nanoscale ZrO2 powders with different impurities. Prominence is given to EPR signals from Zr3? ions (samples without chromium impurities), Cr5? ions (samples with chromium impurities), and signals from polarons, which are localized on surface of nanoscale particles. A number of new effects, which have both fundamental and applied importance, are studied. Although spectroscopic characteristics of Zr3? and Cr5? ions are similar, influence of annealing on EPR signals of these ions is different. An annealing in the temperature range of 200–900?C leads to monotonic increase of Zr3?-ions number. Annealing temperature, which corresponds to appearance of the EPR Zr3? signals, for samples with different impurities is different. Annealing curves of EPR signals caused by Cr5? ions have an extremum in temperature range of 500–600?C. Temperature of Cr5? ion signals appearance and rate of decrease of these signals for T???600?C depend on amount of the impurities in the samples under investigation. Impacts of oxygen vacancies, hydroxyl group, impurity diffusion, and phase transformations in ZrO2 on EPR characteristics of Zr3+ and Cr5+ ions are analyzed. Effect caused by yttrium influence on internal mechanical stresses in zirconia nanoparticles is discovered. As shown, the Cr5? ions can be used as markers providing information on mechanical stresses in zirconia structure. As revealed, the X-ray irradiation leads to oxidation of chromium ions (Cr3????Cr5?). An annealing of samples in hydrogen at Т???250?C leads to essential decrease of chromium-ion number in Cr5? charge state. However, subsequent annealing of these samples in air leads to increase of Cr5?-ions number. An annealing in hydrogen leads to appearance of EPR signals caused by polarons associated with electroconductive areas, which form on surface of nanoparticles. Mechanisms and physical nature of mentioned effects are discussed. As shown, the obtained results can be used for optimization of synthesis technologies and testing of materials and products fabricated on the base of zirconia.