Synthesis and characterisation of some layered and perovskite

Gurusinghe, Nicola Narmada Muthumanike (2013). Synthesis and characterisation of some layered and perovskite. University of Birmingham. Ph.D.

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Abstract

The perovskites LaSr\(_2\)Fe\(_2\)SbO\(_9\) and La\(_2\)Sr\(_2\)Fe\(_3\)SbO\(_1\)\(_2\) crystallise in P2\(_1\)/n space group with Fe\(^3\)\(^+\) 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 Ln\(_2\)SrFe\(_2\)O\(_7\) (Ln = La, Nd, Eu) and La\(_2\)BaFe\(_2\)O\(_7\) 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 La\(_2\)BaFe\(_2\)O\(_7\) and Nd\(_2\)SrFe\(_2\)O\(_7\) 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 CaMnO\(_3\)\(_-\)\(_\delta\) and SrFeO\(_3\)\(_-\)\(_\delta\) 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 SrFeO\(_3\)\(_-\)\(_\delta\) , but only the higher phosphate levels of CaMnO\(_3\)\(_-\)\(_\delta\) phases. The anion incorporation induced some mixed ion valencies but failed to introduce extra oxygen vacancies.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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