Rational design, crystal structure, and frustrated magnetism of the Ge-containing YbFe 2 O 4 -type layered oxides In 2 Zn 3- x Co x GeO 8 (0 ≤ x ≤ 3).

YbFeO-type layered oxides have attracted tremendous interest because the unique crystal comprises two distinct geometrically frustrated triangular cation-sublattices. Herein, a series of YbFeO-type materials InZnCoGeO (0 ≤ ≤ 3) were rationally designed and experimentally synthesized for the first time. The crystal structures of InZnCoGeO were investigated comprehensively by Rietveld refinements against high-resolution monochromatic Cu K XRD data. Zn, Co, and Ge cations are distributed randomly on the [MO] bilayer and possess a trigonal bipyramid (TBP) coordination geometry. Because Co has an unpaired electron in the d orbital and a larger electronegativity than Zn, Co-to-Zn equivalent substitution in InZnCoGeO results in more compact MO-TBPs, which is the origin of anisotropic lattice expansion and contraction along the and axes, respectively. The Co moments in the [MO] bilayer are strongly AFM coupled and geometrically frustrated, therefore resulting in a spin-glass magnetic transition at around = 20 K for InZnCoGeO, while a long-range AFM ordering is established for InCoGeO with a Néel temperature of 53 K, attributed to the significantly enhanced AFM interactions and increased In/Co anti-site disordering, as compared to those in InZnCoGeO.