Molecular Dynamics Study Of Compression And Shear Properties Of Bi₂Te₃

Thermoelectric material is a kind of new functional material, and can achievedirect conversion between heat and electricity. Thermoelectric devices are green, safe,and reliable, which has wide application prospects. In all kinds of thermoelectricmaterials, Bi2Te3is the first thermoelectric material which has already been using inthe commercial application. In the service environment of the thermoelectric device,the thermoelectric material is inevitably in the long-term cyclic loading, which willlead to the declined mechanical stability and further lead to the failure of thethermoelectric material. Thus, study of mechanical properties of Bi2Te3thermoelectric material is important for its industrial application. Compression andshear properties of Bi2Te3are investigated to reveal the effect of Van Der WaalsBonding on mechanical properties of Bi2Te3, providing an important theoretical basisfor developing the highly efficient and stable Bi2Te3thermoelectric devices.Along the c axis of crystal lattice, Bi2Te3has periodic quintuple layers “-Te1-Bi-Te2-Bi-Te1-” which are connected by Van der Waals bonding. In this paper,the molecular dynamics method has been employed to study the mechanicalproperites of cuboid single-crystal bulk Bi2Te3under compressive and shear loads.The emphasis are put on the effects of the Van der Waals bonding on the deformationand failure mechanism. The results show that the Van der Waals bonding plays adominant role on the mechanism of deformation, and fundamentally determines thecompressive ultimate stress and fracture strain. Furthermore, compressive load alongand perpendicular to the c axis can lead to quite different failure modes, which can bedistinguished by their specific effects on the deformation of the Van der Waalsbonding. However, only models with the compressive load perpendicular to the c axisdramatically demonstrate the strain rate effect on the stress–strain curves, justaccording to its poor structural stability. Different from compression, it is evident tofind the strain rate effect in all the shear models because of the easy slip of Van derWaals bonding, which may also hint the possibility of brittle-ductile transition.Obviously, much more work should be done on the modification of moleculardynamics models, such the systems of large deformation and polycrystal.