Influence Of Thermoelectric Properties Research For In₄Se₃ Via Doping

Environmentally friendly thermoelectric?TE?materials that directly convert heat into electricity undoubtedly play an important role as a global sustainable energy solution,and have attracted extensive attention.The efficiency of TE conversion can be defined ZT = S2T/?·?,where S,p,T,and ? are the Seebeck coefficient,electrical resistivity,absolute temperature,and thermal conductivity?including electronic thermal conductivity ?e and lattice thermal conductivity ?l?,respectively.In₄Se₃ is an anisotropy quasi-two-dimensional layered compound and a promising TE material.With its suitable bandgap,high Seebeck coefficient,and low thermal conductivity,much research interest has been hence shifted to this new class of TE materials.Most work in the last decade about In₄Se₃ has focused on polycrystalline compounds for more easily synthesized polycrystalline In₄Se₃ compounds do not have an anisotropy problem,and a strong reduction of ? by interface of polycrystalline has been observed.In this work,we focus on the In₄Se₃ class and study the substitution of different lattice site.Meanwhile,we also study the relationship between the TE performance and temperature,substituted site,carrier concentration?ne?,microstructure.Series of In_4-xYb_xSe₃?x = 0.01-0.09?,In_4-xM_xSe₃?x = 0.01-0.05??M = Dy,Y?,In_4xSe_3-3x?YbCl₃?_x?x = 0.03-0.07?,In_4-xSe_3-x?AI?_x?x = 0.01-0.09??A = Na,K?,In_3.97Se_2.97?NaI?_0.03Yb_y?y = 0-0.05?and In_4-xNi_xSe₃?x = 0.01-0.1?are synthesized through the two-step solid state methods and hot pressing.The relationship between thermal,electrical transport properties and composition,microstructure has been investigated and some results have been gained:?1?The synthesis process for material preparation is laid down and pure In₄Se₃ is obtained,which are explored by various measurements,and experimental data are in consist with previous work.It suggests that the synthetic process for In₄Se₃ and In₄Se₃ based compounds is reasonable.?2?The In4 site is energetically most favorable for Yb,and the solid solubility limit of Yb in In4 is around 0.05 mol.Upon the value other In sites like Inl-In3 are substituted,which would cause increased volume.The Fermi-level pinning is formed within the valence band and conduction band to make Yb behaved as monovalent,which is valid for buffer solutions in ne,Moreover,the introduction of Yb results in the significant enhancement of S via resonance states,which can be bound states capture carrier,and the reduction of the ? via low-frequency long wave phonon scattering,which cause ZT optimized.It implies that despite reduction in ne,Yb cationic substitution in In₄Se₃ is an effectively way to improve TE properties.Significantly enhancement in S can also observed in other cationic substituted rare earth elements like Dy,Y,and the solid limitation of YbCl₃ in In₄Se₃ is relatively low.?3?The carrier concentration?ne?can be enhanced via the introduction of alkali metal iodide in In₄Se₃ lattice,however mobility??e?would be reduced via strong point defects scattering originates from the impurity atoms,and hence the influence of resistance???is uncertain.TE properties can be enhanced via adjusting S and p,which is caused by the introduction of Nal and Yb simultaneously.?4?Ni atoms are substituted for In3 site preferably energetically and those atoms are dissolved in these phases and cause their unit cell reduced.On the one side,Ni can show donor activity,and on the other side with the substitution of Ni on the In site,more Se atoms stably bonded with Ni atoms may reduce the quantity of donor-like defect.In addition,there is no significant enhancement in In₄Se₃ lattice by the magnetism.