| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1505453 | Solid State Sciences | 2011 | 6 Pages |
A polycrystalline stoichiometric La2ZnTiO6 double-perovskite oxide, white in color, has been prepared by soft-chemistry procedures, followed by annealing in air at 1150 °C. This oxide has been treated in an H2/N2 flow at 900 °C to obtain a reduced specimen, blue in color, with a La2Zn1−xTi1+xO6 composition, as demonstrated in a structural studied conducted from neutron powder diffraction data, very sensitive to the contrast between Zn and Ti. Both perovskites crystallize in the monoclinic P21/n space group, with unit-cell parameters related to a0 (ideal cubic perovskite, a0 ≈ 3.8 Å) as a ≈ 2a0,b ≈ c ≈ √2a0. Both oxides are fully oxygen-stoichiometric, as demonstrated from the refinement of the oxygen occupancy factors. The sample treated in air presents an anti-site Zn/Ti disordering of about 10%, meaning that 10% of Ti atoms occupy the 2c Zn positions and viceversa. However, for the reduced sample, the amount of Zn at 2d Ti sites is only 7.6(2)%, whereas there is 10.8(2)% of Ti at the Zn sites. This means that the reduced sample is, globally, Zn defective, with a Ti/Zn ratio of 1.066 and a composition La2Zn0.968Ti1.032O6. This fact implies the partial reduction of Ti4+ to Ti3+ upon ZnO segregation from the crystal structure. A certain electronic conductivity would be expected from the presence of Ti3+–Ti4+ mixed valence, although it could not be measured due to the reactivity of the reduced perovskite in the usual laboratory conditions. The magnetic susceptibility indicates a paramagnetic behavior, thus confirming the presence of Ti3+ ions in the structure.
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