Hay Think learned from the Institute of Metal Research of the Chinese Academy of Sciences that researchers such as Researcher Li Bing and Researcher Zhang Zhidong and their collaborators discovered that copper phosphide (CuP2) crystals have both high sound velocity and low thermal conductivity, which are comparable to conventional materials with low thermal conductivity. The characteristics of low sound velocity and soft material form a sharp contrast. The discovery of this new material is expected to be applied in occasions with good rigidity and thermal insulation at the same time. The research results were recently published in Nature Communications.
Materials with high thermal conductivity have important applications in cooling system heat dissipation and thermal management of electronic components, while materials with low thermal conductivity are often used to build an adiabatic environment. Electrons, magnons, and lattices can all conduct heat. As the most basic heat-conducting carrier of solid materials, the greater the speed of sound, the greater the thermal conductivity.
The study found that the layered crystal material copper phosphide (CuP2) has a sound velocity similar to that of the classic semiconductor material gallium arsenide (GaAs), but the thermal conductivity is one order of magnitude lower. In response to this abnormal behavior, researchers systematically studied the lattice dynamics of the crystal using inelastic neutron scattering technology, and revealed from the atomic level that this abnormal behavior originated from the weakly bonded local vibration mode of Cu atom pairs. During the research process, the researchers presented a complete lattice dynamics image, which provided a guarantee for a deep understanding of the abnormal heat conduction behavior of the material.
Researchers from the Institute of Metals of the Chinese Academy of Sciences used the POWGEN diffractometer of the Spallation Neutron Source at Oak Ridge National Laboratory to study the crystal structure of the material. The study found that CuP2 has a layered structure, the network composed of P atoms and the Cu atomic layer are alternately arranged, and the Cu atoms form isolated pairs of atoms, and the distance between the atoms is relatively long. The researchers used the BL04B2 spectrometer of the Japanese high-energy synchrotron radiation facility to obtain the pair distribution function of the material. The analysis showed that there was no atomic disorder in the system, thus eliminating the scattering effect of atomic disorder on phonons. Researchers have grown a large single crystal and used the time-of-flight spectrometer Pelican and the thermal neutron triaxial spectrometer Taipan of the Australian Nuclear Science and Technology Organization to select three Brillouin zones and systematically study the lattice dynamics of the material. , The dispersion relationship obtained by the experiment is completely consistent with the first-principles calculation results.
In terms of lattice dynamics, the Cu atom pair presents a weakly bonded localized vibration mode, which softens sharply as the temperature rises, showing strong anharmonicity. In terms of the dispersion relationship, an anti-crossing feature was found, indicating that this weakly bonded local vibration mode strongly scatters longitudinal acoustic phonons. Because acoustic phonons are the main participants in heat conduction, especially longitudinal acoustic phonons with sound speeds up to 6243 m s-1. Therefore, the scattering of longitudinal acoustic phonons by this mode leads to a lower phonon lifetime, which offsets the contribution of high sound velocity to thermal conductivity, which is the direct cause of the low thermal conductivity of the crystal.