Leveraging Polymorphism in YbCuBi to Map Transport and Elastic Properties

AMX Zintl compounds with the hexagonal
ZrBeSi
structure have gained significant attention for their remarkable vacancy
tolerance and low thermal conductivity. Their 2D honeycomb sublattice,
composed of M–X covalent bonds, is believed
to contribute to high anharmonicity and unusual thermal transport
properties. In this study, we explore the temperature-dependent polymorphism
of YbCuBi as a model system to investigate the relationship between
the structure and elastic and thermal transport properties in AMX Zintls. YbCuBi undergoes a structural transition from
the “flat” Cu–Bi layers in the ZrBeSi structure
to corrugated layers in the LiGaGe structure below 410 K, resulting
in a distortion of its centrosymmetric structure. To probe the effects
of this crystallographic transition, we employ inelastic neutron scattering
and temperature-dependent resonant ultrasound spectroscopy. These
experimental findings, coupled with first-principles calculations
and thermal conductivity measurements, allow us to elucidate a direct
relationship between corrugation of the honeycomb lattice and the
observed changes in elastic and thermal transport properties. These
insights can be extended to other Zintl phases with similar structure
types, providing a platform for the rational design of functional
materials with tailored thermal properties.