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. In particular, their 2D honeycomb sublattice, composed of M-X covalent bonds, is believed to support protected electronic transport channels and contribute to their unusual thermal transport properties. However, the precise relationship between bonding behavior and elastic and thermal transport properties remains poorly understood.

In this study, we explore the temperature-dependent polymorphism of YbCuBi to investigate the origins of its anomalous elastic and thermal transport properties. YbCuBi undergoes a structural transition from the flat honeycomb structure to the corrugated LiGaGe-structure below 423 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 covalent bonding behavior and the observed changes in elastic and thermal transport properties.