Glass Formation In Eutectic Systems And Syntheses And Performance Of Glassy Te-based Thermoelectric Materials

As a new type of energy conversion material,thermoelectric materials have involved the interest of researches in search of new materials with higher thermoelectric performance,because of the world energy shortage and the environmental pollution.However,the higher thermal conductivity of the conventional crystalline thermoelectric materials limited the further improvement of the thermoelectric performance and the application of the thermoelectric devices.Fortunately the amorphous materials are proven to have a lower thermal conductivity than the crystalline materials.In order to obtain a higher thermoelectric performance,glassy Te-based thermoelectric materials were therefore chosen for studying the glass-forming ability of Te-based thermoelectric materials and the effect of thermal conductivity of glassy Te-based thermoelectric materials on its thermoelectric performance in this paper.Due to the low glass forming ability of the Te-based thermoelectric materials,the idea of multicomponent was chosen to enhance the complexity of the system to synthesize this kind of amorphous alloy.We used the multicomponent systems and guided from the experience on glass-forming to establish the eutectic system.The binary molecular liquids such as methyl-o-toluate and methyl-p-toluate were chosen to study the eutectic system via dielectric measurement first.It was found that the composition with the fragility minima revealed a negative deviation,and the maximum deviation occurred near the eutectic point,but was off-eutectic.Combined with the lower liquid temperature near the eutectic point of the eutectic system,it anticipated that the composition with a higher viscosity would occur at the eutectic point,namely,the best glass forming region was not located at the eutectic composition.So,the phenomenon that the best glass forming region deviated from the eutectic composition can be explained by kinetic.The previous results provided a guide for us to determine the best composition of the glass formation in eutectic system and were therefore applied in the study of the bulk glass of the narrow gap Te-based alloys in binary eutectic systems.Two types of Te-based compounds were chosen as starting materials to establish the binary systems.The first type: Bi₂Te₃,Sb₂Te₃,In₂Te₃ and Ga₂Te₃,and the second type: Cu₂ Te,Ag₂Te,SnTe and PbTe.Then the Te-based alloy ribbons were fabricated by vacuum melting and melt spinning.X-ray diffraction and differential scanning calorimetry were used for the identification of glass formation.It was found that the solid solution system of Bi₂Te₃-Sb₂Te₃ can not form glass under this experimental condition,and the eutectic systems of Cu₂Te?Ag₂Te?-SnTe?PbTe?were also hard to form glass.In contrast,the In₂Te₃-SnTe?PbTe?systems had partial content of amorphous,and the composition of the best glass-forming ability was located at 65mol% In₂Te₃.Furthermore,a perfect amorphous state was successfully obtained in Ga₂Te₃-SnTe?PbTe?system.The best glass-forming regions were located near 32-34mol% Ga₂Te₃,the glass transition temperature was 210?,and the supercooled liquid region was 47?.?2?The glass forming ability of positive mixed heat systems?eg,Cu₂Te-PbTe?in the Te-based binary eutectic systems was much lower than that the negative mixed heat systems?eg,Ga₂Te₃-SnTe?.The bulk glass?SnTe?₆₈?Ga₂Te₃?₃₂ were synthesized via spark plasma sintering and the thermal conductivity were measured with TC-7000 H apparatus.The results showed that the thermal conductivity of?SnTe?₆₈?Ga₂Te₃?₃₂ bulk glass was significantly lower than that of the crystalline state,and which was comparable to that of the state-of-the-art data.