Abstract
Abstract Ruddlesden-Popper n=2 member phases Sr3-xYxFe1.25Ni0.75O7-δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as-prepared at 1300 C under N2(g) flow and samples subsequently air-annealed at 900 C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mössbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mössbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K-1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
Original language | English |
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Article number | 18834 |
Pages (from-to) | 45-54 |
Number of pages | 10 |
Journal | Journal of Solid State Chemistry |
Volume | 227 |
DOIs | |
State | Published - Jul 2015 |
Externally published | Yes |
Funding
The authors acknowledge the “Consortium for Crystal Chemistry, C3” within the Röntgen-Ångström cluster, Swedish research Council nos. VR 2011-6512 , VR 2012-5240 for providing financial support. Mrs. M.-T. Gerhards is thanked for carrying out the DTA/TG measurements. A. Mahmoud acknowledges the Forschungzentrum Jülich for an international postdoctoral grant.
Funders | Funder number |
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Forschungzentrum Jülich |
Keywords
- Crystal structure
- Electrical conductivity
- Mössbauer spectroscopy
- Oxygen non-stoichiometry
- Ruddlesden-Popper structure
- Thermal expansion