Calcium substitution in rare-earth metal germanides with the hexagonal Mn5Si3 structure type. structural characterization of the extended series RE5–xCaxGe3 (RE=Rare-earth metal)

Abstract

Reported are the synthesis and the structural characterization of an extended family of rare-earth metal–germanides with a general formula RE5–xCaxGe3 (RE=Y, Ce–Nd, Sm, Gd–Tm and Lu; x<2). All twelve phases are isotypic, crystallizing with the Mn5Si3 structure type (Pearson index hP16, hexagonal space group P63/mcm); they are the Ca-substituted variants of the corresponding RE5Ge3 binaries. Across the series, despite some small variations in the Ca-uptake, the unit cell volumes decrease monotonically, following the lanthanide contraction. Temperature dependent DC magnetization measurements reveal paramagnetic behavior in the high temperature range, and the obtained effective moments are consistent with free-ion RE3+ ground state, as expected from prior studies of the binary RE5Ge3 phases. The onset of magnetic ordering is observed in the low temperature range, and complex magnetic interactions (ferromagnetic/ferrimagnetic) can be inferred, different from the binary phases RE5Ge3, which are known as antiferromagnetic. In order to understand the role of Ca in the bonding, the electronic structures of the La5Ge3 and the hypothetical compounds La2Ca3Ge3 and La3Ca2Ge3 with ordered metal atoms are compared and discussed.