Symmetry mode analysis of distorted polar/nonpolar structures in A-site ordered SmBaMn2O6 perovskite
13 August 2021
We present a comprehensive structural study of the charge-orbital ordering and magnetic phase transitions observed in the A-site ordered SmBaMn2O6 perovskite combining synchrotron radiation x-ray powder diffraction and symmetry-adapted modes analysis. InSmBaMn2O6, successive phase transitions in charge, spin, and lattice degrees of freedom take place with decreasing temperature at TCO1380K,TCO2190K, and TN250K.
The main difference between the two charge-ordered phases concerns the stacking sequence along the c axis, which is double for the high temperature charge-ordered phase and has led to controversy in the literature. We show that both charge-ordered phases are pseudosymmetric with respect to the ideal undistorted tetragonal structure of A-site ordered RBaMn2O6 perovskites and lead to two nonequivalent Mn sites. However, the charge segregation stabilizes at about 0.35e in the low temperature charge-ordered phase, clearly below the nominal separation of one charge unit between Mn3+ and Mn4+ and undergoes a prominent increase in the high temperature charge-ordered phase when warming above 250K.
The two Mn sites are anisotropic in both charge-ordered phases but the analysis of the active modes discloses that only the low temperature charge-ordered phase displays a Jahn-Teller-like distortion for one of the Mn sites. In addition, this low temperature charge-ordered phase has polar symmetry compatible with ferroelectricity along the a axis.
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Symmetry mode analysis of distorted polar/nonpolar structures in A-site ordered SmBaMn2O6 perovskite

J. Blasco, G. Subías, J. L. García Muñoz, F. Fauth, M. C. Sánchez, and J. García

Phys. Rev. B 103, 214110 – Published 21 June 2021
DOI: 10.1103/PhysRevB.103.214110

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