Swinging Symmetry, Multiple Structural Phase Transitions, and Versatile Physical Properties in RECuGa3 (RE = La–Nd, Sm–Gd)

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• 作者：Udumula Subbarao ; Sudhindra Rayaprol ; Rebecca Dally ; Michael J. Graf ; Sebastian C. Peter
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：January 19, 2016
• 年：2016
• 卷：55
• 期：2
• 页码：666-675
• 全文大小：684K
• ISSN：1520-510X

文摘

The compounds RECuGa₃ (RE = La–Nd, Sm–Gd) were synthesized by various techniques. Preliminary X-ray diffraction (XRD) analyses at room temperature suggested that the compounds crystallize in the tetragonal system with either the centrosymmetric space group I4/mmm (BaAl₄ type) or the non-centrosymmetric space group I4mm (BaNiSn₃ type). Detailed single-crystal XRD, neutron diffraction, and synchrotron XRD studies of selected compounds confirmed the non-centrosymmetric BaNiSn₃ structure type at room temperature with space group I4mm. Temperature-dependent single-crystal XRD, powder XRD, and synchrotron beamline measurements showed a structural transition between centro- and non-centrosymmetry followed by a phase transition to the Rb₅Hg₁₉ type (space group I4/m) above 400 K and another transition to the Cu₃Au structure type (space group Pm3?m) above 700 K. Combined single-crystal and synchrotron powder XRD studies of PrCuGa₃ at high temperatures revealed structural transitions at higher temperatures, highlighting the closeness of the BaNiSn₃ structure to other structure types not known to the RECuGa₃ family. The crystal structure of RECuGa₃ is composed of eight capped hexagonal prism cages [RE₄Cu₄Ga₁₂] occupying one rare-earth atom in each ring, which are shared through the edge of Cu and Ga atoms along the ab plane, resulting in a three-dimensional network. Resistivity and magnetization measurements demonstrated that all of these compounds undergo magnetic ordering at temperatures between 1.8 and 80 K, apart from the Pr and La compounds: the former remains paramagnetic down to 0.3 K, while superconductivity was observed in the La compound at T = 1 K. It is not clear whether this is intrinsic or due to filamentary Ga present in the sample. The divalent nature of Eu in EuCuGa₃ was confirmed by magnetization measurements and X-ray absorption near edge spectroscopy and is further supported by the crystal structure analysis.