Size and morphology effects on the high pressure behaviors of Mn₃O₄ nanorods

Abstract

The high-pressure behaviors of Mn3O4 nanorods were studied by high pressure powder synchrotron X-ray diffraction and Raman spectroscopy. We found the initial hausmannite phase transforms into the orthorhombic CaTi2O4-type structure,...

Pressure tuning the Jahn-Teller transition temperature in NaNiO$_2$

“…This is comparable with a similar JT-distorted material with edge-sharing octahedra, CuMnO 2 , which has bulk modulus 116(2) GPa. 16 It is, however, substantially less than the reported bulk modulus for ZnMn 2 O 4 of 197(5) GPa, 14 and although there are several different reported values for Mn 3 O 4 depending on phase and morphology, [11][12][13] all are higher than what we report for NaNiO 2 . LaMnO 3 is not entirely comparable owing to the LaO 12 units and corner-sharing octahedra, but for reference it has a reported bulk modulus of 108(2) GPa.…”

“…While the latter is a well-documented property of JT-distorted materials, the former is in contrast to the JT distortion in LaMnO 3 . 2 NaNiO 2 is more resistant to pressure than other similar materials, having a higher bulk modulus (B = 119.6(5) GPa at 290 K) than similar perovskites, 3,4 Prussian Blue analogues, 7 and layered honeycomb structures, 50 although its bulk modulus is very similar to JT-distorted edge-sharing CuMnO 2 , 16 and is less than Mn 3 O 4 , [11][12][13] NiO, 58 and ZnMn 2 O 4 . 14 NaNiO 2 also displays a much smaller magnitude of dT JT dP than LaMnO 3 , with LaMnO 3 shifting T JT from ∼750 K at ambient pressure to room temperature in 12 GPa 2 compared with a very small shift from ∼480 K at ambient pressure in NaNiO 2 .…”

“…Here we describe three different examples classes, all containing JT-active d 4 Mn 3+ . Mn 3 O 4 , a spinel containing both Mn 3+ and Mn 2+ , has been found to exhibit different pressure-dependence of JT-distorted octahedra depending on morphology; for instance, in single-crystal Mn 3 O 4 the JT disortion survives to 60 GPa, 11 whereas there are observed transitions to JT-free phases at much lower pressures in powdered 12 and nanorod 13 Mn 3 O 4 .…”

Structural Stability and Properties of Marokite-Type γ-Mn3O4

“…The latter EOS goes a bit above the data points beyond 40 GPa. Previous structural investigations of γ-Mn 3 O 4 reported significantly smaller bulk modulus values for B 0 ′ = 4, e.g., B 0 = 166.6 GPa for powder, and B 0 = 176 GPa for nanorods . The difference is probably related to the sample morphology (defects, vacancies, etc.)…”

“…Given the structural similarity in the ambient-pressure spinel phases of Fe 3 O 4 and Mn 3 O 4 , as well as the similarity in their orthorhombic high-pressure polymorphs, which are composed of linear chains of oxygen octahedra and trigonal prisms, one could anticipate the existence of similar homological series of mixed-valence manganese oxides, which are structurally linked to the high-pressure phase of Mn 3 O 4 with Pbcm symmetry (space group #57; Z = 4). − This Pbcm phase is isostructural to the CaMn 3+ 2 O 4 mineral discovered in Morocco and accordingly named “marokite”. It can be identified as γ-Mn 3 O 4 after the known conventional tetragonal spinel, α-Mn 3 O 4 (space group #141 I 4 1 / amd ; Z = 4), and the high-temperature cubic spinel, β-Mn 3 O 4 (space group #225 Fm 3̅ m , Z = 4). , Note that a recently discovered orthorhombic distortion (space group #70 Fddd ; Z = 4), which is concurrent with magnetic ordering below 42 K, can be assigned as δ-Mn 3 O 4 .…”