Synthesis and characterisation of some layered and perovskite

• Main Author: Gurusinghe, Nicola Narmada Muthumanike
• Published: University of Birmingham 2013
• Subjects: 540; QD Chemistry
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.567804

The perovskites LaSr₂Fe₂SbO₉ and La₂Sr₂Fe₃SbO₁₂ crystallise in P2₁/n space group with Fe³⁺ occupying the two crystallographically distinct six-coordinate sites in a ratio of approximately 1:2. Neutron diffraction data suggest a G-type long-range antiferromagnetism in both materials at 2 K and 300 K. The A site cation ordering in Ln₂SrFe₂O₇ (Ln = La, Nd, Eu) and La₂BaFe₂O₇ increases as the mismatch in A site cation size increases. These phases exhibit long-range antiferromagnetic ordering at 300 K and 2 K; the magnetic moments in La₂BaFe₂O₇ and Nd₂SrFe₂O₇ gradually rotate in the temperature ranges 210 K to 190 K and 17 K to 9 K, respectively. The fluorine incorporation into these phases happens via anion insertion and anion substitution. The partial cation ordering or large overall size of the A site cations allows accommodation of more F⁻ ions causing no change to the Fe oxidation state. Both CaMnO₃₋δ and SrFeO₃₋δ are amenable to phosphate and sulphate anion incorporation. The unit cell sizes increase with the increase of dopant level. The oxy-anion insertion stabilises the cubic structure in all doped phases of SrFeO₃₋δ, but only the higher phosphate levels of CaMnO₃₋δ phases. The anion incorporation induced some mixed ion valencies but failed to introduce extra oxygen vacancies.