As predicted and more: modulated channel occupation in YZn(5+x )

Like many complex intermetallic phases, the crystal structures of REZn(5+x ) compounds (RE = lanthanide or Group 3 element) based on the EuMg(5) type have gradually unfolded. The original reports described a complex hexagonal structure with an unusual combination of tetrahedrally close-packed regions and open spaces, as well as observations of superstructure reflections. More recently, we reinvestigated the structure of YZn(5), reclassifying it as the EuMg(5+x )-type compound YZn(5+x ) (x ≃ 0.2), in which disordered channels run along c through the spaces formerly considered open. In addition, DFT-chemical pressure (DFT-CP) analysis of ordered models of YZn(5+x ) highlighted paths for communication between neighboring channels setting the stage for superstructure formation. Herein, the experimental elucidation of this effect is presented with the synthesis and structure determination of a modulated form of YZn(5+x ). By slow-cooling samples of YZn(5+x ) from the annealing temperature, crystals were obtained that exhibit satellite reflections with the modulation wavevector q = [Image: see text] a* + [Image: see text] b* + 0.3041c*. Structure solution and refinement using a (3+1)D model in superspace group P 31c( [Image: see text] σ(3))00s reveals incommensurate order in the structure’s channels. Here, two Zn sites associated with the channels are present, each with discontinuous atomic domains that are slanted in the x (3) x (4) plane. Their slanting corresponds to adjustments along the c axis for the presence or absence of close neighbors along that axis, while the occupation patterns of neighboring channels are shifted by [Image: see text] of the modulation period. These features follow earlier predictions from CP analysis, highlighting how this approach can be used predictively in search of new phenomena.