The Effect of Donor Doping with Ti4+ on the Oxygen Absorption Properties of h-YMnO3
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In this thesis, the effect of donor doping with Ti4+ on the oxygen absorption properties in the hexagonal rare-earth magnanite h-YMnO3 was studied and compared to undoped compounds of the same material class. Bulk-sized h-YMnO3 and h-YMn0.85Ti0.15O3 (2-17 um), synthesized through solid state synthesis from binary oxides, and nano-sized h-YMnO3, h-YMn0.85Ti0.15O3 and h-DyMnO3 (18.7-25.5 nm), synthesized through a sol-gel synthesis with citric acid, were analyzed in situ in oxidizing and reducing conditions investigating at the changes in structural, gravimetric and electrochemical properties. The structural changes were measured using HT-XRD, where the change in a and c lattice parameters were analyzed both at varying and constant temperature. The gravimetric changes were measured using TGA, where the change in mass was analyzed during heating and cooling in O2. The electrochemical changes were analyzed using DC conductivity and Seebeck coefficient measurements during heating and cooling in O2 and N2. The results in the study show a thermal stabilization of interstitial/absorbed oxygen with increasing a parameter and decreasing c parameter. Substitution of Y3+ with Dy3+ expands both the a and c parameter, increasing the thermal stabilization of Oi by around 100°C. Donor doping of h-YMnO3 with 15% Ti4+ expands the a parameter and contracts the c parameter, increasing the thermal stabilization of Oi by 300°C for the nano-sized compounds and around 500°C for the bulk-sized compounds. Donor doping with 15% Ti4+ did not increase the oxygen absorption capacity in h-YMnO3, but the kinetic properties of h-YMnO3 were greatly increased with Ti-doping. The electrochemical measurements showed that it was possible to tune the type of conductivity (n, p) in h-YMn0.85Ti0.15O3 by the thermal and atmospheric history of the material.