Phonon Symphony of Stacked Multilayers and Weak Bonds Lowers Lattice Thermal Conductivity
Ni Ma, Zhou Zhang, Pengfei Nan, Wei Bai, Kai Li, Jiyin Zhao, Shiming Zhou, Binghui Ge, Jiong Yang, Chong Xiao, Yi Xie
Abstract
Abstract Controlling lattice vibrations to obtain intrinsic low thermal conductivity play a critical role in thermal management of electronic and photonic devices, energy converters, and thermal insulation, which necessitates exploring new compounds and a thorough understanding of their chemical structure, bonding, and lattice dynamics. Herein, a new chalcogenide, Ga 6 Cr 5 Se 16 , shows intrinsic low lattice thermal conductivity κ lat , which crystallizes in the monoclinic phase ( C 2/ m ) with the stacked inverse GaSe 4 layers ( g '), close‐packed Cr 3+ Se 6 layers ( c ), GaSe 4 layers ( g ) and loosely‐stacked Cr 2+ Se 6 layers ( c ') along the c ‐axis. In this structure, a wide variety of chemical bonding is arranged in each layer, such as covalent Ga–Se, covalent Cr 3+ –Se, and weaker Cr 2+ –Se bonding, which endow it with a large phonon symphony by strong coupling of soft acoustic and low‐lying optical phonons. As a result, Ga 6 Cr 5 Se 16 realizes an intrinsic low κ lat of 0.79 W m − 1 K − 1 at 323 K, which is almost four times, or twice lower than that of Cr 3 Se 4 (2.95 W m − 1 K − 1 ), or Cr 2 Se 3 (1.56 W m − 1 K − 1 ), Ga 2 Se 3 (1.36 W m − 1 K − 1 ) at 323 K, respectively. These insights will offer comprehensive understanding of the phonon propagation in complex layered chalcogenides, and also shed useful light on future design of low‐κ lat solids.