Synthesis, Crystal Chemistry and Magnetism of the Metal-rich Borides MxRh7-xB3 (M = Cr, Mn, Ni; x = 0.39 - 1) with Th7Fe3-type Structure

Abstract

The title compounds are synthesized by arc‐melting of the elements and characterized by powder XRD and single crystal XRD of Cr0.78Rh6.22B3 and Mn0.39Rh6.61B3.

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) with Th7Fe3-type structure

“…The phase analysis confirmed the expected Th 7 Fe 3 structure type for all loaded compositions and isotypism with the recently published Cr x Rh 7 À x B 3 (x¼0.78) phase [7]. However, all products were slightly contaminated by a side phase which was identified to be the intermetallic solid solution (Rh/Ru) 1 À x Cr x (x¼0.5) in the quaternary phases and ruthenium metal in the ternary rhodium-free phase (see Table 1).…”

“…This distance is similar to the average value found in all other ternary phases containing ruthenium or rhodium and adopting the Th 7 Fe 3 structure type. [3][4][5][6][7] Even shorter metalboron distances were already found; for example in the ternary phases ScRh 3 B (2.04Å) [10] and Ti 2 Rh 6 B (2.02Å) [11], but in these phases, boron resides in an octahedron instead of a trigonal prism. Concerning the metal-metal contacts, two types have to be considered: the T2-T2 distances (average 2.62Å), where the T2 site accommodates more chromium than any other metal site, are shorter than other metal-metal distances.…”

“…Generally, ternary Rh-rich phases, M x Rh 7 À x B 3 (M ¼Cr, Mn, Fe, Co, Ni) have x c E1, whereas ternary Ru-rich phases, M x Ru 7 À x B 3 (M¼Mn, Fe, Co, Ni) have x c r0.5. [3][4][5][6][7] Fig. 3 shows the crystal structure of the new quaternary complex solid solution Cr x (Rh 1À y Ru y ) 7À x B 3 .…”

“…These studies have led recently to the first itinerant ferromagnetic borides of this structure type, FeRh 6 B 3 and CoRh 6 B 3 , with ordering temperatures of 240 and 150 K, respectively [6]. Pauli paramagnetism has been observed in M 0.5 Ru 6.5 B 3 (M ¼Cr, Mn, Co, Ni) [5] and M x Rh 7 À x B 3 (M¼Cr, Ni) [7] and an additional temperature-dependent behavior was observed in NiRh 6 B 3 and Mn 0.5 Ru 6.5 B 3 at low temperatures. The crystal structures of these phases have revealed a strong M/T site preference.…”

“…The targeted phases comprise those crystallizing with the Th 7 Fe 3 structure type [2] whose general formula M x T 7 À x B 3 (M ¼Cr, Mn, Fe, Co, Ni; T¼Ru, Rh) [3][4][5][6][7] implies a substitution of a 4d transition metal T by a 3d element M in the binary phase T 7 B 3 . These studies have led recently to the first itinerant ferromagnetic borides of this structure type, FeRh 6 B 3 and CoRh 6 B 3 , with ordering temperatures of 240 and 150 K, respectively [6].…”