• PDF / 236,254 Bytes
• 3 Pages / 612 x 792 pts (letter) Page_size
• 51 Downloads / 243 Views

DOWNLOAD

REPORT

---

The p h a s e d i a g r a m of t h e p s e u d o b i n a r y P b T e - P b S e s y s t e m has b e e n r e i n v e s t i g a t e d by t h e r m a l a n a l y s i s of h o m o g e n i z e d liquid and s o l i d a l l o y s a m p l e s and by t h e r m o d y n a m i c c a l c u l a t i o n of the l i q u i d u s - s o l i d u s gap. The o b s e r v e d liquidus a r r e s t t e m p e r a t u r e s v a r y m o n o t o n i c a l l y and s u b l i n e a r l y with c o m p o s i t i o n and a r e in e x c e l l e n t a g r e e m e n t with the v a l u e s r e p o r t e d by G r i m e s (1965). The s o l i d u s a r r e s t t e m p e r a t u r e s h o w e v e r a r e s i g n i f i c a n t l y a b o v e the v a l u e s of the two p r e v i o u s i n v e s t i g a t i o n s b y E l a g i n a and A b r i k o s o v (1956) and b y G r i m e s (1965). The l i q u i d u s s o l i d u s gap n e v e r e x c e e d s 0.13 m o l e f r a c t i o n and shows e x c e l l e n t a g r e e m e n t with the v a l u e s c a l c u l a t e d f r o m the i d e a l l i q u i d u s - s o l i d u s equation. The r e c e n t l y r e p o r t e d l i n e a r v a r i a t i o n with c o m p o s i t i o n of the l a t t i c e p a r a m e t e r of s o l i d s o l u t i o n s is c o n f i r m e d . T H E a l l o y s of the IV-VI s e m i c o n d u c t i n g compounds P b T e and PbSe f o r m a c o m p l e t e s e r i e s of s o l i d s o l u tions with cubic N a C l - t y p e c r y s t a l s t r u c t u r e . 1'2 C o n s i s t e n t with c o m p l e t e s o l u b i l i t y , the l a t t i c e p a r a m e t e r 3 and the e n e r g y gap 4 have b e e n found to v a r y l i n e a r l y with c o m p o s i t i o n . Two s u b s t a n t i a l l y d i f f e r e n t p h a s e d i a g r a m s h o w e v e r have b e e n r e p o r t e d for the p s e u d o b i n a r y P b T e - P b S e s y s t e m , F i g . 1. By t h e r m a l a n a l y s i s and p h o t o m i c r o g r a p h y of a n n e a l e d a l l o y s , E l a g i n a and A b r i k o s o v z o b t a i n e d liquidus and s o l i d u s c u r v e s s h o w ing a b r o a d m i n i m u m at about 900~ and 0.18 m o l e f r a c t i o n PbSe and a t w o - p h a s e l i q u i d - s o l i d f i e l d r e a c h ing a width of about 0.21 m o l e f r a c t i o n in the m i d d l e r a n g e of c o m p o s i t i o n s . In a m o r e r e c e n t t h e r m a l a n a l y s i s s t u d y , h o w e v e r , G r i m e s s found no e v i d e n c e of a m i n i m u m and r e p o r t e d v a l u e s of the l i q u i d u s - s o l i d u s gap a s high a s 0.35 m o l e f r a c t i o n . The p r e s e n t i n v e s t i g a t i o n w a s i n i t i a t e d d u r i n g a g e n e r a l s t u d y of the p h a s e d i a g r a m s and t h e r m o d y n a m i c p r o p e r t i e s of b i n a r y and p s e u d o b i n a r y s y s t e m s of i n t e r e s t in c r y s t a l growth of a l l o y s e m i c o n d u c t o r s . A g e n e r a l e x p r e s s i o n for the t h e r m o d y n a m i c r e l a t i o n s h i p b e t w e e n l i q u i d u s and