Thermoelectric Properties Of InBr,AgBr,and SnX(X=S,Se,Te): The First-principles Study

Energy crisis is an important contradiction in today's society.Environmental pollution is a huge threaten.The new energy has been intersted in scientists and it become a hot spot.Thermoelectric materials is a type of new energy material,which can direct converse thermal and electrical energy with no noise,no wear,safe and reliable way.In this paper,we studied InBr,AgBr and TlI-type SnX(X = S,Se,Te)based on the first-principles calculation method of density functional theory and semi-classical Boltzmann theory.In this paper,we use VASP package to optimize the structure of the three materials to research the lowest energy structure.The WIEN2 k package calculates the electronic structure of the material based on FP-LAPW method.The BoltzTraP code can calculate the transport properties using the semi-classical Boltzmann theory.The lattice structure of InBr is similar to the high temperature phase SnSe.But InBr has an In-In bond along the c-axis between the two InBr layer structures.This means that InBr may have a higher thermoelectric properties along c-axis.We calculated the electronic structures and transport properties of InBr using first-principles calculation and BoltzTraP code.The electron relaxation time of InBr was calculated by deformation potential.InBr has a large bandgap in 0GPa.Hence,we control the electronic structure of InBr by pressure.The best thermoelectric properties of InBr for p-type and n-type is in 7GPa and 2GPa,respectively.The highest ZT values for p-and n-type InBr at 700 K achieved 1.6 and 2.1,respectively.Thus we infer that InBr is a promising thermoelectric material.AgBr is a type of useful chemical material,but as a thermoelectric material,few people are involved.Only an experiment research in 1950 s.We studied Ag Br and found that it might have good thermoelectric properties.We found that Ag Br has a ZT value achieve 1.02.In the calculation,we use Fermi integral,considering the Fermi level change caused by carrier concentration and calculating the relaxation time more accurately.In addition,we considerd Dagdale's model and fit the thermal conductivity.This way is more accurate than minimun lattice thermal conductivity instead of thermal conductivity.SnSe is a thermoelectric material with high thermoelectric properties,which has been concerned recent years.The high temperature phase SnSe will change from room temperature phase at about 800 K.Zhao et al.found that the high temperature phase of SnSe have high thermoelectric properties with the ZT reached 2.6.The high temperature phase SnSe with TlI-type structure,we study the thermoelectric properties of SnX(X = S,Se,Te)with the same family S and Te instead of Se.The results show that the three materials have similar electronic structures,and the band gap decreases from SnS to SnTe,which makes SnTe have high conductivity.In addition,SnTe has a smaller lattice thermal conductivity than SnSe due to the heavier masses of Te atoms.SnTe have larger power factor than SnSe and a lower minimum thermal lattice conductivity,which may be a promising thermoelectric material.The problem of TlI-type Sn Te is that not synthesized in the experiment until now.But our calculations show that SnTe have a negative formation energy and stability elastic properties.This suggested the TlI-type SnTe is promising to be synthesize and apply in future.