Metal Nitrides Grown from Ca/Li Flux: Ca₆Te₃N₂ and New Nitridoferrate(I) Ca₆(Li_xFe_1–x)Te₂N₃

Abstract

Two new tellurium-containing nitrides were grown from reactions in molten calcium and lithium. The compound Ca6Te3N2 crystallizes in space group R3̅c (a = 12.000(3)Å, c = 13.147(4)Å; Z = 6); its structure is an anti-type of rinneite (K3NaFeCl6) and 2H perovskite related oxides such as Sr3Co2O6. The compound Ca6(LixFe1-x)Te2N3 where x ≈ 0.48 forms in space group P42/m (a = 8.718(3)Å, c = 6.719(2)Å; Z = 2) with a new stuffed anti-type variant of the Tl3BiCl6 structure. Band structure calculations and easily observable red/green dichroic behavior indicate that Ca6Te3N2 is a highly anisotropic direct band gap semiconductor (Eg = 2.5 eV). Ca6(LixFe1-x)Te2N3 features isolated linear N-Fe-N units with iron in the rare Fe(1+) state. The magnetic behavior of the iron site was characterized by magnetic susceptibility measurements, which indicate a very high magnetic moment (5.16μB) likely due to a high degree of spin-orbit coupling. Inherent disorder at the Fe/Li mixed site frustrates long-range communication between magnetic centers.

An inverse Ruddlesden-Popper nitride Ca7(Li1−xFex)Te2N2 grown from Ca flux

“…2(b). Noteworthy is that Fe in the 6-1-2-3 phase can be considered as a cationic atom with a rare formal charge of +1 (d 6 s 1 configuration), as confirmed by susceptibility data and theory calculations [19]. Yet the same is not true for the 7-1-2-2 phase, which in fact is a metallic phase.…”

“…However, each Li/Fe in the 6-1-2-3 structure has direct bonding interaction with two electronegative N atoms with a distance of 1.86 Å. This could yield Fe-N-Fe super-exchange interactions as indicated by susceptibility data [19]. In contrast, Li/Fe in perovskite-type layer of This type structure features alternately stacking NaCl-type A'X slabs and the perovskite-type ABX3 slabs along the long axis.…”

“…Yet the same is not true for the 7-1-2-2 phase, which in fact is a metallic phase. (2) The Li/Fe-Li/Fe separation in the 6-1-2-3 phase is c/2 = 3.36 Å [19]. However, each Li/Fe in the 6-1-2-3 structure has direct bonding interaction with two electronegative N atoms with a distance of 1.86 Å.…”

“…2(a), the structure of Ca7(Li0.32(1)Fe0.68 1 Table 3). Simply judging from the formula of Ca7(Li0.32(1)Fe0.68(1))Te2N2, the title 7-1-2-2 phase seems to have a certain underpinned relationship with Ca6Li0.48Fe0.52Te2N3 [19], or in short, 6-1-2-3 phase.…”

“…Among [18] have remarkable magnetic anisotropy and coercivity, which are desired for functional magnetic materials. Unlike the infinite N-(Li/Fe)-N chains, discrete N-(Li/Fe)-N linear blocks surrounded by Ca ion were discovered in the newly synthesized Ca6(Li1−xFex)Te2N3 [19,20], which demonstrates the variety of possible coordination environments for the (Li/Fe)-N units.…”