Phase relations in the system Pb-Sn-Se
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P . ZLOMANOV, W I L L I A M B. W H I T E , AND RUSTUM ROY
P h a s e e q u i l i b r i a h a v e b e e n d e t e r m i n e d i n t h e p o r t i o n o f t h e P b - S n - S e s y s t e m b o u n d e d by t h e c o m p o s i t i o n s Pb-Sn-SnSe-PbSe. T h e P b S e - S n S e join is quasibinary w i t h o n l y s m a l l d e v i a t i o n s f r o m s t o i c h i o m e t r y . T h e t e r n a r y p h a s e b o u n d a r i e s l i e c l o s e t o t h e P b - S n side o f t h e d i a g r a m . S u b s o l i d u s r e l a t i o n s a r e s h o w n by a s e r i e s o f i s o p l e t h a l s e c t i o n s .
CONSIDERABLE
i n t e r e s t h a s b e e n s h o w n in Pbl_xSnxSe a l l o y s w h i c h have a composition-dependent b a n d g a p . ~' e I n o r d e r t o a d j u s t t h e s e m i c o n d u c t i n g c h a r a c t e r i s t i c s o f t h e s e m a t e r i a l s by v a r y i n g t h e a l l o y c o m p o s i t i o n s , it i s i m p o r t a n t t o k n o w t h e p h a s e d i a gram o f t h e t e r n a r y s y s t e m P b - S n - S e . T h e P b - S e syst e m c o n t a i n s only o n e c o m p o u n d , l e a d s e l e n i d e , w i t h a m a x i m u m m e l t i n g t e m p e r a t u r e of 1080 ° t o 1084°C.3' 4 A l e a d - r i c h e u t e c t i c e x i s t s a t 0 . 0 1 3 a t . pct Se a t 0 . 2 ° C b e l o w t h e m e l t i n g p o i n t o f l e a d ( 3 2 7 . 4 ° C ) . F o r the c o m p o s i t i o n s P b S e - S e , t h e e u t e c t i c is d e g e n e r a t e d a n d practically coincides with t h e melting point of pure s e l e n i u m (220°C).S T h e b i n a r y j o i n P b - S n h a s b e e n o u t l i n e d a s a s i m p l e e u t e c t i c type w i t h a e u t e c t i c p o i n t a t 183°C a n d 26.1 a t . p c t P b . A t t h e e u t e c t i c t e m p e r a t u r e t h e s o l u b i l i t y o f t i n in l e a d i s 29 a t . pct a n d t h e s o l u b i l i t y o f l e a d in t i n i s 1.65 a t . p c t . T h e r e a r e t w o c o m p o u n d s , S n S e a n d S n S e z , in the S n - S e s y s t e m w i t h c o n g r u e n t m e l t i n g p o i n t s at 8 8 0 ° a n d 6 7 5 °, r e s p e c t i v e l y . T h e e u t e c t i c p o i n t b e t w e e n the c o m p o u n d s is at 61 at. pct S e a n d 6 2 5 ° C . T h e m o n o t e c t i c t e m p e r a t u r e of S n S n S e c o m p o s i t i o n s is 8 2 2 ° C . T h e r e is a m i s c i b i l i t y g a p b e t w e e n I 0 a n d 50 at. pct. T h e e u t e c t i c t e m p e r a t u r e s in the S n - S n S e a n d S n S e 2 - S e r a n g e s d o not d i f f e r f r o m the m e l t i n g p o i n t s of p u r e tin ( 2 3 2 ° C ) a n d s e l e n i u m (220°C).6 T h e P - T - X d i a g r a m s of the P b - S e a n d S n - S e s y s t e m s have been described. 7-H T h e T - X d i a g r a m for the P b S e - S n S e s y s t e m w a s m e a s u r e d b y D T A t e c h n i q u e s , b y X - r a y a n a l y s i s of a n n e a l e d a n d q u e n c h e d s a m p l e s , a n d f r o m the first-tof r e e z e c o m p o s i t i o n s for d i r e c t i o n a l l y f r o z e n s
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