Thermoelectric material having crystal grains well oriented in certain direction and process for producing the same

Abstract

Thermoelectric material is produced through a process sequence including a liquid quenching, a primary solidification such as a hot pressing or extrusion and an upset forging; although the C-planes of the crystal grains are directed in parallel to the direction in which the force is exerted on flakes during the hot pressing/extrusion, the a-axes are randomly directed; the a-axes are oriented in a predetermined direction through the upset forging; this results in improvement of electric resistivity without reduction in the figure of merit.

1 . Thermoelectric material containing at least one first element selected from the group consisting of Bi and Sb and at least one second element selected from the group consisting of Te and Se and incidental impurities, and including crystal grains having C-planes inclining with respect to a certain direction at 45 degrees or less, said crystal grains occupying an area of a surface of said thermoelectric material in parallel to said certain direction, the ratio of said area to the entire area of said surface being equal to or greater than 90%.  
   
   
       2 . The thermoelectric material as set forth in  claim 1 , in which the composition thereof is expressed as Bi x Sb y Te z , and said ratio is equal to or greater than 93%.  
   
   
       3 . The thermoelectric material as set forth in  claim 2 , in which said x, y and z are 0.4, 1.6 and 3, respectively, and said ratio is equal to or greater than 96%.  
   
   
       4 . The thermoelectric material as set forth in  claim 2 , in which said x, y and z are 0.45, 1.55 and 3, respectively, and said ratio is equal to or greater than 93%.  
   
   
       5 . The thermoelectric material as set forth in  claim 2 , Te is excessively added to said thermoelectric material at 1% by mass, and said ratio is equal to or greater than 94%.  
   
   
       6 . The thermoelectric material as set forth in  claim 1 , in which the composition thereof is expressed as Bi x Te y Se z .  
   
   
       7 . The thermoelectric material as set forth in  claim 6 , in which SbI 3  is added to said thermoelectric material at 0.06% by mass, and said ratio is equal to or greater than 94%.  
   
   
       8 . The thermoelectric material as set forth in  claim 1 , in which the composition thereof is expressed as Bi w Sb x Te y Se z , and said ratio is equal to or greater than 93%.  
   
   
       9 . The thermoelectric material as set forth in  claim 8 , in which said w, x, y and z are equal to 1.9, 0.1, 2.6 and 0.4, respectively, and said ratio is equal to or greater than 95%.  
   
   
       10 . The thermoelectric material as set forth in  claim 8 , in which said w, x, y and z are equal to 1.9, 0.1, 2.7 and 0.3, respectively, and said ratio is equal to or greater than 93%.  
   
   
       11 . The thermoelectric material as set forth in  claim 1 , in which at least one element selected from the group consisting of I, Cl, Hg, Br, Ag and Cu is added to said thermoelectric material.