• Fredrickson, Rie Takagi
• Fredrickson, Daniel

Abstract

<jats:p>Like many complex intermetallic phases, the crystal structures of REZn<jats:sub>5+<jats:italic>x</jats:italic></jats:sub> compounds (RE = lanthanide or Group 3 element) based on the EuMg<jats:sub>5</jats:sub> 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<jats:sub>5</jats:sub>, reclassifying it as the EuMg<jats:sub>5+<jats:italic>x</jats:italic></jats:sub>-type compound YZn<jats:sub>5+<jats:italic>x</jats:italic></jats:sub> (<jats:italic>x</jats:italic> ≃ 0.2), in which disordered channels run along <jats:italic>c</jats:italic> through the spaces formerly considered open. In addition, DFT-chemical pressure (DFT-CP) analysis of ordered models of YZn<jats:sub>5+<jats:italic>x</jats:italic></jats:sub> 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<jats:sub>5+<jats:italic>x</jats:italic></jats:sub>. By slow-cooling samples of YZn<jats:sub>5+<jats:italic>x</jats:italic></jats:sub> from the annealing temperature, crystals were obtained that exhibit satellite reflections with the modulation wavevector <jats:bold>q</jats:bold> = {1 3}<jats:bold>a*</jats:bold> + {1 3}<jats:bold>b*</jats:bold> + 0.3041<jats:bold>c*</jats:bold>. Structure solution and refinement using a (3+1)D model in superspace group <jats:italic>P</jats:italic><jats:overline>3</jats:overline>1<jats:italic>c</jats:italic>({1 3}\,\!{1 3}σ<jats:sub>3</jats:sub>)00<jats:italic>s</jats:italic> 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 <jats:italic>x</jats:italic><jats:sub>3</jats:sub><jats:italic>x</jats:italic><jats:sub>4</jats:sub> plane. Their slanting corresponds to adjustments along the <jats:italic>c</jats:italic> axis for the presence or absence of close neighbors along that axis, while the occupation patterns of neighboring channels are shifted by {1 3} 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.</jats:p>

Topics

• impedance spectroscopy
• compound
• phase
• density functional theory
• annealing
• intermetallic
• Lanthanide