Ba₄KFe₃O₉: A Novel Ferrite Containing Discrete 6-Membered Rings of Corner-Sharing FeO₄ Tetrahedra

Abstract

Single crystals of a new iron containing oxide, Ba4KFe3O9, were grown from a hydroxide melt and the crystal structure was determined by single crystal x-ray diffraction. This ferrite represents the first complex oxide containing isolated 6-member rings of corner sharing FeO4 tetrahedra. Mössbauer measurements are indicative of two tetrahedral high-spin Fe3+ coordination environments. The observed magnetic moment (~3.9 BM) at 400 K is significantly lower than the calculated spin-only (~5.2 BM) value indicating the presence of strong antiferromagnetic interactions in the oxide. Our density functional calculations confirm the strong antiferromagnetic coupling between adjacent Fe3+ sites within each 6-member ring and estimate the nearest neighbor spin exchange integral as ~200 K; next nearest neighbor interactions are shown to be negligible. The lower than expected effective moment for Ba4KFe3O9 calculated from χT data is explained as resulting from the occupation of lower lying magnetic states in which more spins are paired. X-band (9.5 GHz) electron paramagnetic resonance (EPR) spectra of powder sample consist of a single line at g~2.01 that is characteristic of Fe3+ ions in a tetrahedral environment, thus, confirming the Mössbauer results. Further analysis of the EPR line shape reveals the presence of two types of Fe6 magnetic species with an intensity ratio of ~1:9. Both species have Lorentzian line shapes and indistinguishable g-factors but differ in the peak-to-peak line widths (δBpp). The line width ratio δBpp(major)/δBpp(minor) ~ 3.6 correlates well with the ratio of the Weiss constants, θminor/θmajor ~ 4.

Stuffed Tridymite Structures: Synthesis, Structure, Second Harmonic Generation, Optical, and Multiferroic Properties

“…The observed magnetic moment of 3.69 μ B compares well with the calculated value of 4.18 μ B corresponding to Fe 3+ (3d 5 ), high spin ( S =5/2). The experimental magnetic moment value is consistent with those observed for Fe 3+ in a tetrahedral coordination environment [47] . For example, magnetic moment values of approximately 3.93 μ B have been observed for antiferromagnetic Ba 4 KFe 3 O 9 [47] .…”

“…The experimental magnetic moment value is consistent with those observedf or Fe 3 + in at etrahedral coordinatione nvironment. [47] For example, magnetic momentv alues of approximately 3.93 m B have been observed for antiferromagnetic Ba 4 KFe 3 O 9 . [47] Similarly, the reported magnetic moments for tetrahedral Fe 3 + in BaFe 4 O 7 and K 0.22 Ba 0.89 Fe 4 O 7 are 3.8 m B and 4.4 m B ,r espectively, [48] which compare well with that observed for the present compound.…”

Polymorphism and Molten Nitrate Salt-Assisted Single Crystal to Single Crystal Ion Exchange in the Cesium Ferrogermanate Zeotype: CsFeGeO4

“…A similar tetrahedral environment is exhibited by Fe(2), which is coordinated to O(3), O(5), O (7), and O(8) with bond lengths 1.835(4), 1.826(3), 1.861(5), and 1.856(5) Å, respectively. These bond lengths are in fair agreement with the Fe−O bond lengths ranging from 1.828 Å−1.896 Å in Ba 4 KFe 3 O 9 , 41 which contains discrete 6membered rings of corner-sharing FeO 4 tetrahedra, as well as other compounds containing iron in tetrahedral, noncentrosymmetric environment. 11,16 Structurally related to (1), (2) also comprises large tunnels that crisscross the crystal structure along the a-, b-, and c-axis; eight-, four-, and six-ring channels run along the a-, b-, and c-axis, respectively, and are occupied by the monovalent cesium ions that provide charge balance for the three-dimensional anionic [FeGeO 4 ] − framework.…”

New high Tc multiferroics KBiFe2O5 with narrow band gap and promising photovoltaic effect

“…(Only a small number of Fe-containing oxides adopt this uncommon ring structure. )23 Between these layers are a sheet of severely distorted [BiO 6 ] 9− octahedra with four Bi–O bond lengths within 2.130–2.345 Å and the other two at 2.712 Å (Bi–O2) and 2.809 Å (Bi–O3) (Supplementary Table S3). Similarly dispersive metal-oxygen distances are common for Bi 3+ -containing compounds due to lone pair electrons2425.…”