The crystal structures of the ternary intermetallics RE 2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE 2Ga2Mg (RE = Tb, Er, Tm, Lu) at 90 K

Zeitschrift für Naturforschung B Pub Date : 2024-06-25 DOI:10.1515/znb-2024-0014

Maximilian Kai Reimann, Jutta Kösters, Tautvydas Bieliauskas, Rainer Pöttgen

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Abstract

The crystal structures of the U3Si2-related intermetallic compounds RE 2Pd2Cd (RE = Nd, Sm, Gd, Dy) and RE 2Ga2Mg (RE = Tb, Er, Tm, Lu) were studied from single crystal X-ray diffraction data at T = 90 K in order to understand the slightly enhanced U 33 displacements of the 2a positions in their room temperature structures. The compounds Sm2Pd2Cd, Gd2Pd2Cd and Dy2Pd2Cd show a decrease of the ratio of U 33 to U 11 for the cadmium atoms, leading to a more isotropic behavior at low temperature, keeping the P4/mbm space group symmetry. Nd2Pd2Cd shows a translationengleiche symmetry reduction to space group P4bm along with a weak puckering effect with shorter (342.7 pm) and longer (345.7 pm) Cd–Nd distances within the Cd@Nd8 square prisms. This new, non-centrosymmetric superstructure variant was also observed for the magnesium compounds Tb2Ga2.069Mg0.931, Er2Ga2.104Mg0.896, Tm2Ga2.097Mg0.903 and Lu2Ga2.173Mg0.827, which show small degrees of Mg/Ga mixing.

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三元金属间化合物 RE 2Pd2Cd（RE = Nd、Sm、Gd、Dy）和 RE 2Ga2Mg（RE = Tb、Er、Tm、Lu）在 90 K 时的晶体结构

根据单晶 X 射线衍射数据，研究了 U3Si2 相关金属间化合物 RE 2Pd2Cd（RE = Nd、Sm、Gd、Dy）和 RE 2Ga2Mg（RE = Tb、Er、Tm、Lu）在 T = 90 K 时的晶体结构，以了解其室温结构中 2a 位置的 U 33 位移略微增强的情况。Sm2Pd2Cd、Gd2Pd2Cd 和 Dy2Pd2Cd 化合物显示出镉原子的 U 33 与 U 11 之比减小，从而在低温下表现出更大的各向同性，保持了 P4/mbm 空间群对称性。Nd2Pd2Cd 在 Cd@Nd8 方棱柱内的 Cd-Nd 间距较短（342.7 pm）和较长（345.7 pm）时，显示出平移棱对称性降低到 P4bm 空间群，同时出现微弱的起皱效应。在镁化合物 Tb2Ga2.069Mg0.931、Er2Ga2.104Mg0.896、Tm2Ga2.097Mg0.903 和 Lu2Ga2.173Mg0.827 中也观察到了这种新的、非中心对称的超结构变体，它们显示出较小程度的镁/镓混合。

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Zeitschrift für Naturforschung B

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