Abstract
Four polar intermetallic compounds belonging to the RE2In1−xLixGe2 (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system have been synthesized by the traditional solid-state reaction method, and their crystal structures have been characterized by single-crystal X-ray diffraction (SXRD) analyses. The isotypic crystal structures of four title compounds adopt the Mo2FeB2-type structure having the tetragonal space group P4/mbm (Z = 2, Pearson code tP40) with three crystallographically independent atomic sites and can be simply described as a pile of the identical 2-dimensioanl (2D) RE2In1-xLixGe2 slabs stacked along the c-axis direction. The substituting Li atom shows a particular site preference for replacing In at the Wyckoff 2a site rather than Ge at the Wyckoff 4g in this crystal structure. As the size of a used rare-earth metal decreases from La3+ to Gd3+ throughout the title system, the Ge-Ge and Ge-In/Li bond distances, both of which consist of the 2D anionic Ge2(In/Li) layer, gradually decrease resulting in the reduction of a unit cell volume. A series of theoretical investigations has been performed using a hypothetical structure model Gd2In0.5Li0.5Ge2 by tight-binding linear muffin-tin orbital (TB-LMTO) method. The resultant densities of states (DOS) value at the Fermi level (EF) suggests a metallic conductivity for this particular composition, and this calculation result is in a good agreement with the formal charge distribution assigning two extra valence electrons for a metal-metal bond in the conduction band. The thorough analyses of six crystal orbital Hamilton population (COHP) curves representing various interatomic interactions and an electron localization function (ELF) diagram indicating the locations of paired-electron densities are also provided in this article.
Highlights
We serendipitously obtained four quaternary polar intermetallics belonging to the RE2 In1−x Lix Ge2 (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system, and all four title compounds crystallized in the Mo2 FeB2 -type structure [16]
Once the crystal structures of the four products were determined as the Mo2 FeB2 -type structure based on the single-crystal X-ray diffraction (SXRD) analysis, we attempted to reproduce these compounds by loading the refined stoichiometric compositions
Four polar intermetallic compounds belonging to the RE2 In1−x Lix Ge2 (RE = La, Nd, Sm, Gd; x = 0.13(1), 0.28(1), 0.43(1), 0.53(1)) system were synthesized by the high-temperature reaction method, and their crystal structures were characterized by SXRD analyses
Summary
A ternary compound Gd5 Si2 Ge2 [10] proves that the giant magnetocaloric effect (MCE) can possibly occur at near room temperature through the first-order magnetic phase transition between the ferromagnetic and paramagnetic phases as a function of temperature. Given that this interesting magnetic phase transition has been proven to be triggered by the crystal structure transformation between the orthorhombic and tetragonal crystal systems, numerous research activities have focused on understanding the correlation among composition-structure-property of the particular ternary solid-solution Gd5 Si2−x Ge2+x system [10,11], as well as various other RE5 Tt4.
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