Crystal and Electronic Structures of MoSi₂-Type CrGe₂ Synthesized under High Pressure

Abstract

Chromium germanides, namely, Nowotny chimney-ladder-phase CrGe1.77 and MoSi2-type CrGe2, were synthesized above 15 GPa or more via laser heating using a diamond anvil cell (LHDAC). MoSi2-type CrGe2, which is the most Ge-rich compound in the Cr–Ge system, crystallizes in the tetragonal structure with a space group of I4/mmm (no. 139) and lattice parameters of a = 3.24919(6) Å and c = 8.0523(3) Å and is isostructural with MoSi2. MoSi2-type CrGe2 has a deep pseudogap caused by the splitting of 3d orbitals with Cr, as evidenced by ab initio calculation. In this article, we have succeeded in synthesizing a binary compound between transition-metal and metalloid elements for the first time at high pressures above 10 GPa using the LHDAC. This pathway opens the possibility to explore more compounds in this system and may provide new insights into the fundamental interaction between these two elements.

Movable triple points and Dirac points in centrosymmetric AB2 (A = Cr, Mo; B = Si, Ge) compounds

“…The AB 2 (A = Cr, Mo; B = Si, Ge) series of compounds have been widely synthesized since 1900 and can stably exist under ambient conditions. [61][62][63][64] They share the tetragonal MoSi 2 -type structure, belonging to the space group I4/mmm (No. 139) [see Fig.…”

Noncentrosymmetric Nowotny Chimney Ladder Ferromagnet Cr4Ge7 with a High Curie Temperature of ∼207 K

“…Among the various itinerant ferromagnets, the simple binary Cr–Te forms a series of self-intercalated phases including CrTe 2 , Cr 5 Te 8 (Cr 1/4 –CrTe 2 ), Cr 2 Te 3 (Cr 1/3 –CrTe 2 ), Cr 3 Te 4 (Cr 1/2 –CrTe 2 ), and CrTe (Cr 1 –CrTe 2 ). , A remarkable feature of these binary ferromagnets is their relatively high T C which, for example, even reaches above room temperature in CrTe 2 (∼310 K), Cr 3 Te 4 (∼320 K), and CrTe (∼340 K) . As a close relative, the binary Cr–Ge system also forms abundant members including Cr 3 Ge, Cr 5 Ge 3 , Cr 11 Ge 8 , CrGe, Cr 11 Ge 19 , Cr 4 Ge 7 , and CrGe 2 , Unfortunately, as compared with Cr–Te, they have been less investigated. Among them, the Nowotny chimney ladder (NCL) FM Cr 11 Ge 19 ( T C ∼ 88 K) crystallizes into the noncentrosymmetric P 4̅ n 2 space group (No.…”

Pressure-Tunable Crystal Structure and Magnetic Transition Temperature of the Nowotny Chimney-Ladder CrGeγ Phase

“…In this study, we have focused on a chromium germanide crystallizing as an NCL phase. The best-known NCL CrGe γ is probably Cr 11 Ge 19 , which is an ambient-pressure phase and an itinerant ferromagnet with a Curie temperature of approximately T C = 86 K. ,− On the other hand, Takizawa et al figured out that Cr 4 Ge 7 , which requires high pressures ( P = 4–5.5 GPa) and temperatures ( T = 800–1000 °C) to form, exhibits ferromagnetism with T C = 270 K. , We have recently synthesized CrGe 1.77 , which is more Ge-rich than Cr 11 Ge 19 (γ = 1.727) and Cr 4 Ge 7 (γ = 1.75), at P = 15 GPa using a laser-heated diamond anvil cell (LHDAC) . The composition of the NCL CrGe γ becomes Ge-rich as the synthesis pressure increases.…”

“…The best-known NCL CrGe γ is probably Cr 11 Ge 19 , which is an ambient-pressure phase and an itinerant ferromagnet with a Curie temperature of approximately T C = 86 K. 4,13−16 On the other hand, Takizawa et al figured out that Cr 4 Ge 7 , which requires high pressures (P = 4− 5.5 GPa) and temperatures (T = 800−1000 °C) to form, 17 exhibits ferromagnetism with T C = 270 K. 18,19 We have recently synthesized CrGe 1.77 , which is more Ge-rich than using a laser-heated diamond anvil cell (LHDAC). 20 The composition of the NCL CrGe γ becomes Ge-rich as the synthesis pressure increases. The modulation structure and composition of the NCL phase are expected to be controlled by synthesis pressure.…”