# Temperature-Dependent Structural Transition in Cu-Intercalated Trigonal CuYbSe2

## TL;DR

This paper studies a temperature-driven structural change in a copper-intercalated compound, revealing a new low-symmetry structure and potential for exotic magnetic behavior.

## Contribution

The discovery of a temperature-dependent structural transition in CuYbSe2 with a new I2/m symmetry and Cu-site vacancy ordering.

## Key findings

- A structural transition occurs at 258 K in CuYbSe2, leading to a lower-symmetry I2/m structure.
- Cu-site vacancy ordering accompanies the transition, altering the crystal symmetry and lattice geometry.

## Abstract

Rare-earth delafossites, ARCh2; A = alkali
metal, R
= rare-earth, Ch = chalcogen which consist of intercalated rare-earth
metal dichalcogenides, host frustrated triangular lattices that are
fertile ground for exotic phenomena. In most cases, the triangular
rare-earth sublattice arises from R-3m (No. 166) structures with three layers of rare-earth metal dichalcogenide
octahedra or P63/mmc (No.
194) structures with two such layers, analogous to those found in
transition metal dichalcogenides. Substituting the alkali metal with
Cu+ yields a distinct trigonal crystal symmetryP-3m1 (No. 164)in these structures.
This symmetry change alters the coordination environment from ASe6 octahedra in R-3m AYbSe2 to CuSe4 tetrahedra in CuYbSe2, resulting
in shortened rare-earth to rare-earth separations and significantly
reduced interlayer distances. Using X-ray single-crystal diffraction,
powder neutron diffraction, resistance, and specific heat measurements,
a structural transition slightly below room temperature (258 K) is
observed. The low-temperature structure is a lower-symmetry I2/m structure, accompanied by partial
Cu-site vacancy ordering. The combination of Cu disorder and the triangular
lattice geometry in CuYbSe2 provides a promising platform
for investigating frustrated magnetism and unconventional transport
phenomena.