One Structure, Two Elements-LuGe2 Superconductor vs Ordinary Metallic Conductor LuSn2. A Case Study on How Site-Selective Germanium for Tin Atom Substitution Leads to Modulating of the Charge Distribution

Jiliang Zhang; Fazhu Ding; Jey-Jau Lee; Guangcun Shan; Svilen Bobev

doi:10.1021/acs.inorgchem.0c01062

One Structure, Two Elements-LuGe₂ Superconductor vs Ordinary Metallic Conductor LuSn₂. A Case Study on How Site-Selective Germanium for Tin Atom Substitution Leads to Modulating of the Charge Distribution

Inorg Chem. 2020 Dec 7;59(23):16853-16864. doi: 10.1021/acs.inorgchem.0c01062. Epub 2020 Sep 24.

Authors

Jiliang Zhang^{1

2}, Fazhu Ding^{3

4}, Jey-Jau Lee⁵, Guangcun Shan^{6

7}, Svilen Bobev¹

Affiliations

¹ Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States.
² Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea.
³ Key Laboratory of Applied Superconductivity and Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
⁴ University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China.
⁵ National Synchrotron Radiation Research Center, Hsinchu 30076 Taiwan, Republic of China.
⁶ School of Instrument Science and Optoelectronics Engineering & Institute of Precision Mechanics and Quantum Sensing, Beihang University, Beijing 100083, People's Republic of China.
⁷ Institute of Experimental Physics, Saarland University, 66123 Saarbrücken, Germany.

PMID: 32970413
DOI: 10.1021/acs.inorgchem.0c01062

Abstract

The substitution of chemically similar elements in a given crystal structure is an effective way to enhance physical properties, but the understanding on such improvements is usually impeded because the substitutions are random, and the roles of the different atoms cannot be distinguished by crystallographic symmetry. Herein, we provide a detailed crystallographic analysis and property measurements for the continuous solid solutions LuGe_xSn_2-x (0 < x < 2). The results show that there is no apparent change of the global symmetry, with the end-members LuGe₂ and LuSn₂, as well as the intermediate LuGe_xSn_2-x compositions adopting the ZrSi₂ type structure (space group Cmcm, Pearson index oC12). Yet, the refinements of the crystal structures from single-crystal X-ray diffraction data show that Ge-Sn atom substitutions are not random, but occur preferentially at the zigzag chain. The patterned distribution of two group 14 elements leads to a significant variation in chemical bonding and charge ordering within the other structural fragment, the 2D square nets, thereby resulting in tuned electron transport. The enhancement is greater than that for the typical Bloch-Gruneisen model and more akin to that for the parallel-resistor model. Magnetization measurements on single crystals show bulk superconductivity in all LuGe_xSn_2-x samples with shielding fractions as high as 90%. Specific heat data confirm the effect to originate from residual metallic tin in the material, indicating that Sn atom substitutions in the 2D square nets cause disruptions of the hypervalent bonding and local anisotropy, which ultimately leads to vanishing of the superconducting state in the end-member LuGe₂. This work sheds light on how the complexity in chemical interactions by two different carbon congeners leads to changes in the physical properties and how they can be correlated with the induced charge distribution. These studies also provide a general approach to modulation of charge density and. thus, of emerging physical properties in other classes of intermetallic systems based on the main-group elements of groups 13 to 15.