Crystal Structure, Li-7 NMR, and Structural Relationship of Two Rare-Earth Metal Richer Polar Intermetallics: La15Ge9Li1.50(16) and La7Ge3

Abstract

Two novel polar intermetallic compounds have been synthesized by a high-temperature reaction method, and their crystal structures have been characterized by both single-crystal and powder X-ray diffractions. La15Ge9Li1 (.50(16)) crystallizes in the hexagonal space group P6(3)mc (Z = 2, Pearson code hP52) with nine crystallographically independent sites in the unit cell, and the lattice parameters are a = 15.516(2) and c = 6.895(2) angstrom. The overall crystal structure can be described as a 3 x 3 x 1 superstructure of the parent compound La5Ge3 adopting the Mn5Si3-type, and such a superstructure transformation should be attributed to the particular ordering patterns of interstitial Li atoms at the Wyckoff 2a and 2b sites with different occupation factors. La7Ge3 also crystallizes in the hexagonal P6(3)mc space group (Z = 2, Pearson code hP20) with three La and one Ge non-equivalent sites in the unit cell. The lattice parameters are a = 10.666(1) and c = 6.357(1) angstrom. The crystal structure of La7Ge3 shares some similarities with La15Ge9Li1.50(16) and its parent compound La5Ge3, such as the one-dimensional (1D) zigzag confacial La-6 octahedra chains and the 1D zigzag La atomic chains. Theoretical investigations using tight-binding linear muffin-tin orbital (LMTO) method provide a comprehensive understanding about electronic structures and chemical bonding of two title compounds based upon density of states (DOS) and crystal orbital Hamilton population (COHP) analyses. The solid-state Li-7 NMR spectrum measurement proves the existence of two independent interstitial Li positions at two distinctive octahedral sites in La15Ge9Li1.50(16).