The Study On The Pressure Control Mechanism Of The Thermoelectric Properties Of Bi₂Se₃with Native Point Defect

With the rapid development of the global economic and industry, energy plays animportant role in the economic and social development. However, energy almostrelies on non-renewable resources. Non-renewable means will be depleted. To makematters worse, these non-renewable can cause environmental pollution. Therefore,new materials have become an important topic and in global materials scientists. Atthe same time, it has become an important object between material scientists. Amongthem, thermoelectric material which can convert the heat and the electricity from eachother, has become an important object is studied by scholars.Recently, Bi2Se3has attracted great interest by people for its high performanceon figure of merit. Natural Bi2Se3is more likely to form native point defect. More ofthem are Se1vacancy (). In practice, the native point defect has much effect on itsfigure of merit. So we need to further study the Se1vacancy defect in Bi2Se3. Theconversion efficiency is characterized by Figure of merit (). The can beexpressed byzT S2T/e l, S is the Seebeck coefficient,、 is thematerials are electrical conductivity and thermal conductivity, the electron thermalconductivity eand the phonon thermal conductivity lconstitute the thermalconductivity, T is the absolute temperature. The high means the betterperformance for the thermoelectric material. We can figure it out that a goodthermoelectric material should have large Seebeck coefficient and large electricalconductivity, but also have small thermal conductivity. But these there parametersinfluence each other in a material. Therefore, we can make changes from pressure.First, our calculation based on first-principles density functional theory derivedthe density of states and charge density of the Se1vacancy defect in Bi2Se3under zeropressure. We found that the Fermi level around appear a peak (e nergy0.154eV),however the perfect Bi2Se3without this peak, this means the carrier concentration isincrease and the band gap get narrow. This benefits the electron transition. Second, we calculating the Se1vacancy defect in Bi2Se3under different pressure,analyze the charge density of the Se1vacancy defect in Bi2Se3under pressure from1Gpa to8Gpa. We found that with the pressure increase the distance betweenquintuple layer decrease, because The quintuple layer are weakly bound to each otherby the van der Waals forces, and between different atomic in each layer involves acovalent contribution and is stronger.Last, we calculate the Seebeck coefficient, power factor and of the Se1vacancy defect in Bi2Se3at300K.We found that the pressure is contribute to enhancethe, especially for n-type Bi2Se3and when the pressure is8Gpa, the temperatureis300K, it has the highest value of is0.85.