Structural and Magnetocaloric Properties of the New Ternary Silicides Gd6M5/3Si3 with M = Co and Ni

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• 作者：Etienne Gaudin ; Sophie Tencé ; Franç ; ois Weill ; Jesus Rodriguez Fernandez ; Bernard Chevalier
• 刊名：Chemistry of Materials
• 出版年：2008
• 出版时间：May 13, 2008
• 年：2008
• 卷：20
• 期：9
• 页码：2972 - 2979
• 全文大小：567K
• 年卷期：v.20,no.9(May 13, 2008)
• ISSN：1520-5002

文摘

Unlike Gd₆Co_5/3Si₃, which is obtained as a single phase after melting of the constituents, annealing under vacuum at 1073 K for 1 month is necessary to prepare the new ternary silicide Gd₆Ni_5/3Si₃. Indeed, after melting, this alloy is a mixture containing mainly Gd₃NiSi₂ and Gd₅Si₃. These two compounds, Gd₆M_5/3Si₃ (M = Co or Ni), crystallize with the hexagonal Ce₆Ni_2−xSi₃-type structure. The crystal structure of Gd₆Ni_5/3Si₃, refined on a single crystal with space group P6₃/m and unit cell parameters a = 11.7433(1) Å and c = 4.1857(1) Å, is characterized by infinite chains of face-shared trigonal prisms [Gd₆] filled by silicon or nickel atoms. These chains run along the c-axis and extend as triangular columns by sharing rectangular faces in the ab-plane. Between these columns, infinite chains of face-shared octahedra of Gd atoms partially are filled by Ni atoms. The strong delocalization of the electron density of Ni observed in these latter chains has been attributed to high steric strains. No diffuse scattering nor superstructure were observed from electron diffraction experiments. The magnetization measurements reveal that (i) Gd₆Ni_5/3Si₃ orders ferromagnetically at 310 K, a Curie temperature higher than that observed for Gd₆Co_5/3Si₃ (T_C = 294 K) and pure gadolinium (T_C = 294 K); (ii) Ni as well as Co carries no magnetic moment; and (iii) these ternary silicides exhibit interesting magnetocaloric properties; for instance, the magnetic entropy (ΔS_m determined by magnetization measurements) of Gd₆Ni_5/3Si₃ is at a maximum around 312 K with values of ΔS_m = −2.93 and –5.72 J/K kg at applied magnetic fields of 2 and 4.8 T, respectively. These properties are compared to those existing for the most famous magnetocaloric materials as Gd or Gd₅Ge₂Si₂.