X-ray and Neutron Structure Determination and Magnetic Properties of New Quaternary Phases RE_0.67Ni₂Ga_5+n-xGe_x and RE_0.67Ni₂Ga_5+n-xSi_x (n = 0, 1; RE = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm) Synthesized in Liquid Ga

Abstract

Liquid Ga was used as a solvent to explore the phase formation between rare-earth metals (REs), Ni, and a tetrelide (Tt = Si, Ge). The reactions were performed in excess liquid Ga at 850 °C. Two new phases of general formulas RE0.67Ni2Ga5 - x Tt x and RE0.67Ni2Ga6 - x Tt x were found and structurally characterized. The Co analogues of the latter RE0.67Co2Ga6 - x Ge x (RE = Y, Gd) were also prepared. Single-crystal X-ray data: The first group of compounds RE0.67Ni2Ga5 - x Tt x crystallizes in the hexagonal space group P63/mmc with a structure related to the RE2 - x Pt4Ga8+ y type (Sm0.53Ni2Ga5 - x Ge x , a = 4.1748(7) Å, c = 16.007(4) Å, V = 241.61(8) Å3, Z = 2; Y0.59Ni2Ga5 - x Ge x , a = 4.1344(11) Å, c = 15.887(6) Å, V = 235.18(12) Å3, Z = 2; Tb0.67Ni2Ga5 - x Si x , a = 4.1415(11) Å, c = 15.843(6) Å, V = 235.33(12) Å3, Z = 2; Ho0.67Ni2Ga5 - x Ge x , a = 4.1491(4) Å, c = 15.877(2) Å, V = 236.71(5) Å3, Z = 2). The second group RE0.67Ni2Ga6 - x Tt x crystallizes in P6̄m2 (Gd0.67Ni2Ga6 - x Ge x , a = 4.1856(10) Å, c = 9.167(3) Å, V = 139.08(7) Å3, Z = 1; Sm0.67Ni2Ga6 - x Si x , a = 4.1976(8) Å, c = 9.159(3) Å, V = 139.76(5) Å3, Z = 1) in a structure related to the ErNi3Al9 structure type with disorder in the RE−Ga plane. Dy0.67Ni2Ga6 - x Ge x crystallizes in space group P3̄1c (a = 7.2536(8) Å, c = 18.308(3) Å, V = 834.21(2) Å3, Z = 6) with partial disorder in the RE−Ga plane. The structures of these two groups of compounds are related to each other and contain similar building motifs, namely Ga n [NiGa2 - x /2Ge x /2]2 slabs and RE0.67Ga monatomic layers which alternate along the c-direction, forming a 3D structure. The parameter x and the position of the tetrelide in the structure were determined by single-crystal neutron diffraction. Complete or partial disorder of the RE and Ga atoms is observed in the RE−Ga plane. The origin of the disorder lies in the extensive and random stacking faults of ordered RE−Ga planes, which apparently slide easily in the ab plane and create an averaged disordered picture. Electrical conductivity and thermopower measurements indicate that these compounds are metallic conductors. The magnetic measurements show antiferromagnetic ordering at ∼3−4 K and Curie−Weiss behavior at higher temperatures with the values of μeff close to those of RE3+ free ions. Strong 2-fold crystal field anisotropy is observed for the heavy RE analogues. The anisotropy constants K 2 para calculated from the Weiss constant anisotropy for heavy RE analogues are reported.

Intermetallics as Zintl Phases: Yb2Ga4Ge6 and RE3Ga4Ge6 (RE=Yb, Eu): Structural Response of a [Ga4Ge6]4− Framework to Reduction by Two Electrons

“…Synthesis: Yb 2 Ga 4 Ge 6 (1) and Yb 3 Ga 4 Ge 6 (2) were first obtained from Yb/Ni/Ga/Ge reactions in liquid Ga, from which the hexagonal phase Yb 0.67 Ni 2 Ga 6Àx Ge x [30,4] (x % 0.67) was isolated in high yield, whereas 1 and 2 were present in only minor quantities. Nevertheless, the formation of 1 and 2 at reaction stoichiometries far from their ideal compositions suggested high stability of their crystal structures.…”

“…The three-dimensional (3D) [Ga 4 Ge 6 ] framework is made up of four-coordinate atoms and conforms to the require- ments of the Zintl concept. According the octet rule, the framework is electron-deficient, as each Ga atom has four neighbors, but only three electrons are available for bonding (see below for Ga and Ge coordination environments).…”

“…We have reported a number of intermetallics grown from Ga flux; these include RENiSi 3 , [1] Sm 2 NiGa 12 , [2] RE 4 FeGa 12Àx Ge x , [3] RE 0.67 M 2 Ga 5 + nÀx Ge x [4] (M = Ni, Co), RE 3 Ga 9 Ge, [5] REMGa 3 Ge (M = Ni, Co), and RE 3 Ni 3 -Ga 8 Ge 3 . [6,7] However, examples of Zintl compounds obtained from molten Ga are relatively scarce and include the clathrate compounds M 8 Ga 16 Tt 30 [8,9] (M = Ba, Sr; Tt = Si, Ge) and the Zintl phase Eu 4 Ga 8 Ge 16 .…”

“…We describe two related Zintl compounds: Yb 2 Ga 4 Ge 6 and RE 3 Ga 4 Ge 6 (RE = Yb, Eu). They contain the [Ga 4 Ge 6 ] 4À(6À) framework and are an interesting example of the power of the Zintl concept in describing how the observed framework structures respond when two electrons are added or removed.…”

Antiferromagnetic Kondo lattice in the layered compoundCePd1−xBi2and comparison to the superconductorHan1, Wan2, Phelan3 et al. 2015Phys. Rev. BSelf Cite122140View full textAdd to dashboardCite

“…The tube was heated to 900 • C in a box furnace and kept at 900 • C for 10 h. A slow-cooling process at the rate 5 • C/h was carried out from 900 • C to 500 • C, and at 500 • C the excess Bi flux was removed by centrifugation. 7 The obtained crystals were shiny silvercolor plates with a typical dimension of 5 × 5 × 0.5 mm and stable in the air.…”