Lithium-filled double-deck layered structure of the RELi_xCu_2-yP₂ (RE = La, Pr, Nd, Gd, Er; 0.82 ≤ x ≤ 1; 1.19 ≤ y ≤ 1.54) series: Experimental and theoretical studies

Five rare-earth metal containing quaternary phosphides in the RELi_xCu_2-yP₂ (RE = La, Pr, Nd, Gd, Er; 0.82 ≤ x ≤ 1; 1.19 ≤ y ≤ 1.54) series were synthesized by using high-temperature synthetic methods, and they were characterized by single-crystal X-ray diffraction. The title compounds crystallize in the trigonal space group P {3} m1 (Z = 1, Pearson code hP6) with four crystallographically independent atomic positions. The overall crystal structure can be described as a "Li-filled" CaAl₂Si₂-type structure, in which a partially occupied Li site is embedded within the "double-deck" layers formed by two anionic components. Tight-binding linear muffin-tin orbital calculations including density of states, crystal orbital Hamilton population, and electron localization function analyses provided rationales for the overall electronic structure and chemical bonding of the title phase. PrLi_0.98(5)Cu_1.54(1)P₂ indicated an antiferromagnetic interaction of Pr at a relatively low temperature with a paramagnetic Curie temperature of -6.8 K and a thermal conductivity of 3.2 W mK^-1 at 323 K. Five rare-earth metal containing quaternary phosphide compounds show the "Li-filled" double-deck-layered structure, in which the Cu and P atoms consist of 2D puckered hexagonal double-deck layers.