Science Daily May 9, 2022
Conventional structure transitions occur from a low symmetry state to a higher symmetry state upon warming. An international team of researchers (USA – Northwestern University, Brookhaven National Laboratory, Germany) found an unexpected local symmetry breaking in the tetragonal diamondoid compound silver gallium telluride. Upon warming, it evolved continuously from an undistorted ground state to a locally distorted state while retaining average crystallographic symmetry. This is a rare phenomenon previously referred to as emphanisis. The distorted state, caused by the weak orbital hybridization of tetrahedral Ag atoms, resulted in their displacement of the tetrahedron center and promoted a global distortion of the crystal structure resulting in strong acoustic–optical phonon scattering and an ultralow lattice thermal conductivity. The findings explain the underlying reason for the unexpectedly low thermal conductivities of silver-based compounds compared to copper-based analogs and provide a guideline to suppressing heat transport in diamondoid and other materials…read more. TECHNICAL ARTICLEÂ
The side view of a basic AgGaTe2 building block (left) shows the silver (Ag) atom at the center of a 3D tetrahedron…Credit: Brookhaven National Laboratory.