Structural and magnetic properties of several cobalt(II) weberites

Complex ceramic structures. I. Weberites

“…Ag 2 MgFeF 7 (Koch & Hebecker, 1988) Imma 4 7.3100 710.335 1 (Yakubovich et al, 1993;Cosier et al, 1970; C2 (Welsch & Babel, 1992;Cosier et al, 1970;Boireau et al, 1993) C2 List of weberite oxides with R A /R B and the relative ionicity of the A-O bond.…”

A Geometrically Frustrated Family of MIIMIIIF5(H2O)2 Mixed–Metal Fluorides with Complex Magnetic Interactions

“…Interestingly, the highest frustration indices for Cr 3+ and Fe 3+ compounds were observed for the compositions with the same number of unpaired electrons: e.g., in CoCrF 5 (H 2 O) 2 ( 2 ) Co 2+ and Cr 3+ have three unpaired electrons and in MnFeF 5 (H 2 O) 2 Mn 2+ and Fe 3+ have five unpaired electrons. Moreover, we estimated frustration indices for the two known weberites Na 2 CoCrF 7 and Na 2 CoFeF 7 , where in contrast to the inverse weberite compounds M II F 6 octahedra form chains. Interestingly, the inverse weberite compounds have higher frustration indices in comparison to the analogous weberite compounds: e.g., | f | is equal to 6.63 and 1.25 for CoFeF 5 (H 2 O) 2 ( 6 ) and Na 2 CoFeF 7 , respectively.…”

“…Moreover, we estimated frustration indices for the two known weberites Na 2 CoCrF 7 and Na 2 CoFeF 7 , where in contrast to the inverse weberite compounds M II F 6 octahedra form chains. Interestingly, the inverse weberite compounds have higher frustration indices in comparison to the analogous weberite compounds: e.g., | f | is equal to 6.63 and 1.25 for CoFeF 5 (H 2 O) 2 ( 6 ) and Na 2 CoFeF 7 , respectively. At the same time Na 2 CoCrF 7 , which contains Cr 3+ , demonstrated a fairly high | f | value (7.27); however, this value is still lower than that for CoCrF 5 (H 2 O) 2 ( 2 ).…”

“…Magnetic frustration is typically observed and studied in select structure types that exhibit geometric frustration, including the pyrochlore, hexagonal tungsten bronze, weberite, and inverse weberite structures. The pyrochlore and weberite structure types bear a relationship to the fluorite structure, AX 2 , and are often described as anion-deficient fluorite superstructures with compositions of A 2 B 2 X 7 for the pyrochlore and weberite structures and ○ 2 B 2 X 5 (H 2 O) 2 (○ = vacancy) for the inverse weberite structure. − The pyrochlore and weberite structures exist as both oxides and fluorides, where the latter, A 2 B 2 F 7 , has attracted attention recently due to the ability of the fluorides, for charge reasons, to accommodate late 3d transition elements, resulting in magnetic frustration as well as intriguing magnetic interactions in systems such as NaCaCo 2 F 7 , NaSrMn 2 F 7 , and NaSrFe 2 F 7 , pyrochlores and Na 2 CoCrF 7 , Na 2 CoFeF 7 , Na 2 NiFeF 7 , and Na 2 MnFeF 7 weberites.…”

“…Two additional important differences are the replacement of two F atoms by water molecules and the absence of A cations (Figure ). ,, Both weberites and inverse weberites have been investigated to understand the concept of coupled magnetic frustration in compositions where two types of cations occupy distinct crystallographic sites. ,,,, In the 1980s, Laligant et al successfully synthesized M II Fe III F 5 (H 2 O) 2 (M II = Fe, Mn, Co, Ni, Zn) using solvothermal methods and their studies indicated that in inverse weberites frustrated magnetism can be induced when both M II and M III have unpaired electrons. ,,,− However, frustrated magnetism properties were studied only for Fe 3+ -based compounds, and those of other inverse weberite structures have not yet been studied.…”