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Structural, vibrational, thermal, and magnetic properties of mullite-type NdMnTiO5 ceramic

Kowsik Ghosh, M. Mangir Murshed, Thomas Frederichs, Naveen K. C. Muniraju, Thorsten M. Gesing

Journal of the American Ceramic Society (2021), 105, 2702-2712

https://doi.org/10.1111/jace.18261

Mullite-type RMn2O5 (R = Y, rare-earth element) ceramics are of ongoing research attention because of their interesting crystal-chemical and magnetic properties. We report nuclear and magnetic structures of NdMnTiO5 together with its spectroscopic, thermogravimetric, and magnetic properties. The polycrystalline sample is prepared by solid-state synthesis and characterized from neutron and X-ray powder diffraction data Rietveld refinements. NdMnTiO5 crystallizes in the orthorhombic space group Pbam with metric parameter a  =  755.20(1) pm, b  =  869.91(1) pm, c  =  582.42(1) pm, and V  =  382.62(1) 106 pm3. The Mn3+ and Ti4+ cations are observed to be located in the octahedral and pyramidal sites, respectively. The vibrational features in these polyhedral sites are characterized by Raman and Fourier transform infrared spectroscopes. The higher decomposition temperature of NdMnTiO5, compared to other RMn2O5 phases, is explained in terms of the higher bond strength of Ti-O bonds than those of Mn-O bonds. Temperature-dependent DC magnetic susceptibility suggests a paramagnetic to antiferromagnetic phase transition at 43(1) K. Inverse susceptibility in the paramagnetic region above 120 K follows the Curie-Weiss law, resulting in a magnetic moment of 6.33(1) μB per formula unit. Neutron diffraction data collected at 7.5 K reveal that the magnetic moments of Nd3+ and Mn3+ in NdMnTiO5 are incommensurately ordered with a propagation vector k = (0, 0.238, 0.117).

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