Linking local structure and properties in perovskites containing equal concentrations of manganese and ruthenium

Abstract

Abstract:The local structures of six perovskite compounds containing equal amounts of manganese and ruthenium on the B-site have been investigated by neutron and X-ray pair distribution function analysis. were also investigated to study the effects of changing the charge of the A-site cation. Although substitution of La 3+ for a divalent alkaline earth ion increases the Mn 3+ content, this series of compounds also shows a relative increase in the concentration of Mn 4+ as the average size of the A-site cation is decreased. In all compounds the octahedra containing Mn 3+ are found to be JahnTeller distorted regardless of whether or not long range orbital ordering is observed, while the Ru-centered octahedra are symmetric. No evidence for short range cation ordering at either the A or B-sites was found for any of the compositions. This study also reports the previously undocumented finding that locally the A-site cations lie closer to the Mn ions than to the Ru ions and this asymmetry appears to be correlated to the degree of octahedral tilting.

Ca2MnRuO6: Magnetic Order Arising from Chemical Chaos

“…Thus, on moving from Sr 2 MnRuO 6 to Ca 2 MnRuO 6 , the calculations indicate a shift of approximately 0.2 electrons from Mn to Ru. These values are consistent with the oxidation states estimated experimentally using X-ray absorption near edge structure spectroscopy and neutron pair distribution function analysis. , …”

“…These values are consistent with the oxidation states estimated experimentally using X-ray absorption near edge structure spectroscopy and neutron pair distribution function analysis. 22,25 Parts (a) and (b) in Figure 3 show the spin-polarized density of states (DOS) for chemically ordered C-type antiferromagnetic Sr 2 MnRuO 6 and ferrimagnetic Ca 2 MnRuO 6 , respectively. The orbital resolved DOS for the Mn 3d and Ru 4d states for the same two compounds are shown in Figure 4a,b.…”

“…This compound magnetically orders in spite of the fact that the Mn and Ru atoms are completely disordered. − Unfortunately, orbital ordering stabilizes a C-type antiferromagnetic structure in Sr 2 MnRuO 6 . If however Sr 2+ is replaced by the smaller Ca 2+ , the magnetic ground state becomes ferrimagnetic. − In this paper we use first principles calculations based on density functional theory (DFT) to understand this unexpected behavior. Our results suggest that Ca 2 MnRuO 6 will be a half-metal, even in the presence of high levels of Mn/Ru disorder.…”

Hybrid Improper Ferroelectricity: A Theoretical, Computational, and Synthetic Perspective

“…There are compositions that do satisfy this lengthy list of strict criteria, which are observed to crystallize with polar P2 1 symmetry. The most widely studied are phases of composition NaLnMnWO 6 (Ln = La, Nd, Tb) (45)(46)(47), which are predicted computationally to exhibit large ferroelectric polarizations (11). However, detailed physical measurements provide no indication of ferroelectric behavior, and other physical signatures of a noncentrosymmetric structure [piezoelectricity, second harmonic generation (SHG)] are weak, suggesting that any polarization present in the materials is small (48).…”