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• 作者：Marina A. Zhuravleva ; X. Z. Chen ; Xiaoping Wang ; Arthur J. Schultz ; John Ireland ; Carl K. Kannewurf ; and Mercouri G. Kanatzidis
• 刊名：Chemistry of Materials
• 出版年：2002
• 出版时间：July 2002
• 年：2002
• 卷：14
• 期：7
• 页码：3066 - 3081
• 全文大小：1012K
• 年卷期：v.14,no.7(July 2002)
• ISSN：1520-5002

文摘

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 at850 ges/entities/deg.gif">C. Two new phases of general formulas RE_0.67Ni₂Ga_5-xTt_x and RE_0.67Ni₂Ga_6-xTt_x werefound and structurally characterized. The Co analogues of the latter RE_0.67Co₂Ga_6-xGe_x (RE= Y, Gd) were also prepared. Single-crystal X-ray data: The first group of compoundsRE_0.67Ni₂Ga_5-xTt_x crystallizes in the hexagonal space group P6₃/mmc with a structure relatedto the RE_2-xPt₄Ga_8+y type (Sm_0.53Ni₂Ga_5-xGe_x, a = 4.1748(7) Å, c = 16.007(4) Å, V = 241.61(8)ų, Z = 2; Y_0.59Ni₂Ga_5-xGe_x, a = 4.1344(11) Å, c = 15.887(6) Å, V = 235.18(12) ų, Z = 2;Tb_0.67Ni₂Ga_5-xSi_x, a = 4.1415(11) Å, c = 15.843(6) Å, V = 235.33(12) ų, Z = 2; Ho_0.67Ni₂Ga_5-xGe_x,a = 4.1491(4) Å, c = 15.877(2) Å, V = 236.71(5) ų, Z = 2). The second group RE_0.67Ni₂Ga_6-xTt_xcrystallizes in Pges/entities/sixmacr.gif">m2 (Gd_0.67Ni₂Ga_6-xGe_x, a = 4.1856(10) Å, c = 9.167(3) Å, V = 139.08(7) ų,Z = 1; Sm_0.67Ni₂Ga_6-xSi_x, a = 4.1976(8) Å, c = 9.159(3) Å, V = 139.76(5) ų, Z = 1) in astructure related to the ErNi₃Al₉ structure type with disorder in the RE-Ga plane.Dy_0.67Ni₂Ga_6-xGe_x crystallizes in space group Pges/entities/thremacr.gif">1c (a = 7.2536(8) Å, c = 18.308(3) Å, V =834.21(2) ų, Z = 6) with partial disorder in the RE-Ga plane. The structures of these twogroups of compounds are related to each other and contain similar building motifs, namelyGa_n[NiGa_2-x/2Ge_x/2]₂ slabs and RE_0.67Ga monatomic layers which alternate along the c-direction, forming a 3D structure. The parameter x and the position of the tetrelide in thestructure were determined by single-crystal neutron diffraction. Complete or partial disorderof the RE and Ga atoms is observed in the RE-Ga plane. The origin of the disorder lies inthe extensive and random stacking faults of ordered RE-Ga planes, which apparently slideeasily in the ab plane and create an averaged disordered picture. Electrical conductivityand thermopower measurements indicate that these compounds are metallic conductors.The magnetic measurements show antiferromagnetic ordering at ~3-4 K and Curie-Weissbehavior at higher temperatures with the values of ges/entities/mgr.gif">_eff close to those of RE³⁺ free ions. Strong2-fold crystal field anisotropy is observed for the heavy RE analogues. The anisotropy constants K₂^para calculated from the Weiss constant anisotropy for heavy RE analogues arereported.