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W.V.

YOUDEL~

The t r a n s p o r t and t h e r m o e l e c t r i c p r o p e r t i e s of bismuth and Bi-12 at. pct Sb alloy powder c o m p a c t s , v a r y i n g in p a r t i c l e size from 100 to 400 mesh, have been d e t e r m i n e d over the t e m p e r a t u r e range 300 to 77 K (liquid nitrogen). F r o m the m e a s u r e d values of r e s i s t i v i t y , Seebeck potential, m a g n e t o r e s i s t a n c e effect and Hall coefficient, the t h e r m a l conductivity, figure of m e r i t , and the charge c a r r i e r m o b i l i t i e s and concentrations a r e d e t e r m i n e d for the c o m p a c t s . The v a l u e s of the t h e r m o e l e c t r i c p a r a m e t e r s , a and Z, for the m u l t i c r y s t a l l i n e powder compacts approach but do not exceed the highest v a l u e s obtained for the single c r y s t a l s .

A knowledge of the effects of m e t a l l u r g i c a l v a r i a b l e s on the behavior of t h e r m o e l e c t r i c m a t e r i a l s is e s s e n t i a l if optimum s t a b i l i t y and p e r f o r m a n c e of t h e r m o e l e c t r i c d e v i c e s is to be r e a l i z e d . In p a r t i c u l a r , the fabrication of solid state devices by r e l a t i v e l y low cost powder compaction p r o c e s s e s is an intriguing p o s s i b i l i t y which m e r i t s c o n s i d e r a t i o n , and has led to s e v e r a l i n v e s t i g a t i o n s on the t h e r m o e l e c t r i c p r o p e r t i e s of powder compacts: e . g . , Penn, ~ Goldsmid and U n d e r wood 2 on Bi2Ses-Bi2Te3 a l l o y s , and Bear e t a l . 3 on b i s muth and Bi-12 at. pct Sb a l l o y s . In the l a t t e r r e l a tively high values for the t h e r m o e l e c t r i c power w e r e obtained for the powder compacts c o m p a r e d to ingot s p e c i m e n s ; however, m e a s u r e m e n t s w e r e r e p o r t e d for r o o m t e m p e r a t u r e only. The p r e s e n t investigation d e s c r i b e s r e s u l t s for b i s muth and Bi-12 at. pct Sb alloy powder c o m p a c t s . M e a s u r e m e n t s have been made of the t e m p e r a t u r e d e pendence (liquid nitrogen to room t e m p e r a t u r e ) of the r e s i s t i v i t y , Hall coefficient, m a g n e t o r e s i s t a n c e effect, and Seebeck coefficient for s p e c i m e n s compacted from different powder s i z e s . F r o m the m e a s u r e d v a l u e s the t e m p e r a t u r e dependence of the following quantities was calculated: e l e c t r o n hole m o b i l i t i e s , c a r r i e r concentration, t h e r m a l conductivity, and t h e r m o e l e c t r i c figure of m e r i t . PREPARATION OF MATERIALS AND SPECIMENS The bismuth and antimony used in this investigation w e r e five nines pure. Powdered m a t e r i a l was p r e p a r e d by machine filing, in a d u s t - f r e e e n c l o s u r e , c a s t r o d s of bismuth and the section with the a p p r o p r i a t e composition from zone r e f i n e d r o d s of Bi-Sb alloy. Subsequent s c r e e n i n g with s t a i n l e s s steel s i e v e s group