Stoichiometry and defect structure of ‘NdMnO₃'’

Abstract

The phase ‘NdMnO₃’ has been synthesised and characterised by a combination of electron probe microanalysis, X-ray and neutron diffraction and H₂-reduction thermogravimetry. NdMnO₃ forms, at ≈1400 °C, over the range Nd_1.00(1)Mn_0.95(1)O_2.92(1) to Nd_0.88(1)Mn_1.00(1)O_2.72(1). Oxygen contents vary in air over the range 700 to 1400 °C and can be varied further, either by high pressure O₂ treatment or by reduction in H₂. The structure of ‘NdMnO₃’ is based on the GdFeO₃ structure with a Jahn-Teller distortion associated with the high proportion of Mn³⁺ ions present. However, it also shows a very varied defect structure; depending on composition and heat treatment, vacancies can form on any one or any two of the three sublattices, Nd, Mn and O and the overall Mn oxidation state can include 2+, 3+ and 4+ contributions. Data on compositional range and defect crystal structure are presented in the form of a novel phase diagram-defect structure map.

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