Mechanochemical Syntheses Of Samarium Telluride And Gadolinium Telluride Materials And Their Thermoelectric Performance

As a new type of energy material,thermoelectric material can directly realize the conversion between thermal energy and electric power.It has great potential in the fields of waste thermal power and refrigeration.As a member of the Lanthanide Tellurides,Samarium Telluride and Gadolinium Telluride have good band structures and electrical conductivity.Because of the complex band structure,the Seebeck coefficient will be large under a high carrier concentrations level.There are much phonon scattering at vacancies and electron-phonon scattering with high carrier concentration level in the complex crystal structure of La_3-xTe₄ that can reduce the lattice thermal conductivity.However,it is difficult to synthesize Lanthanide Telluride in liquid phase or by melting method because of the active chemical properties of Lanthanide metals.In this paper,we use powder metallurgy to synthesis Samarium Telluride and Gadolinium Telluride and adjust sintering parameters and element ratios to explore the correlation between sintering parameters,element ratios and thermoelectric properties.Sintering for 45 min at 900?is the most suitable parameter in synthesizing Samarium Telluride.Materials can crystallize completely with moderate grain size and porosity under this parameter and telluride will be lost little,too.Between the Samarium(Sm)to Tellurium(Te)ratio of 2 to 3 and 3 to 4,the crystal structure is Sm₃Te₄(I-43d space group,a=9.25(?)).As the Sm proportion increased,the Sm Te(Fm-3m space group,a=5.68(?))structure appeared and become the only phase when Sm:Te=1:1.Semiconductor characteristics convert from P-type to N-type.We calculated that the Fermi level(?)is larger than 1,indicating that Samarium Tellurium is a degenerate semiconductor material with a high degree of degeneracy.Finally,we studied Sm_3.6Te₄,and get the highest thermoelectric figure of merit(ZT)of 0.025 at 1024kelvin(K).Sintering for 45 min at 900?is the most suitable parameter in synthesizing Gadolinium Telluride.Between the Samarium(Sm)to Tellurium(Te)ratio of 2 to 3 and 3 to 4,the crystal structure is Gd₃Te₄(I-43d space group,a=9.533(?)).As the Gd proportion increased,the Gd Te(Fm-3m space group,a=6.15(?))structure appeared and become the only phase when Gd:Te=1:1.Semiconductor characteristics convert from P-type to N-type.We calculated the Fermi level(?)is larger than 1,showing that Samarium Tellurium is a degenerate semiconductor material with a high degree of degeneracy.The simulated band structure of Gd Te shows that the f-layer electrons of the Gd element make the main contribution to the electrical transport.Finally,we obtained the ZT in Gd_3.7Te₄ of 0.362 at 973 K.In general,both Samarium Telluride and Gadolinium Telluride are worth studying.The binary system of Gadolinium Telluride reaches a high ZT value(0.362),and the application temperature is high.So it is expected that further research and exploration,such as doping,will promote the development of high-temperature thermoelectric materials and devices.