The Nd-Rh system
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T h e p h a s e d i a g r a m of t h e N d - R d s y s t e m w a s d e t e r m i n e d b y p o w d e r X - r a y d i f f r a c t i o n , m e t a l l o graphic and differential thermal analysis techniques. Eight intermediate phases occur in the s y s t e m . A n F e s C t y p e p h a s e i s f o u n d to b e p r e s e n t a t 19.5 a t . p c t R h . N d s R h h a s a s t r u c t u r e s i m i l a r to t h a t of L a s R h . T h e o t h e r i n t e r m e d i a t e p h a s e s of t h e s y s t e m a r e NdsRh3 (low a n d h i g h t e m p e r a t u r e m o d i f i c a t i o n s ) , Nd4Rha, Nd 53Rh47 (C r B - t y p e ), NdRha (MgC u 2 - t y p e ) , a n d NdRh3 ( C e N i s - t y p e ) . T h e p h a s e s Nd4Rh, N d s R h , Nd4Rhs, NdRh2, a n d NdRh3 m e l t c o n g r u e n t l y . NdsRh3 a n d N d R h a r e f o r m e d t h r o u g h p e r i t e c t i c r e a c t i o n s . T h e i n t e r m e d i a t e p h a s e s of t h e N d - R h s y s t e m a r e c o m p a r e d w i t h t h o s e of t h e L a - R h , N d - C o , a n d N d - N i s y s t e m s . L a t t i c e v a c a n c i e s a r e p o s t u l a t e d t o b e p r e s e n t i n t h e p h a s e s Nd4Rh a n d N d R h . THE phase equilibria and the crystal structural feat u r e s of t h e i n t e r m e d i a t e p h a s e s in t h e N d - R h s y s t e m a r e n o t k n o w n . O n l y two p h a s e s of t h e s y s t e m , N d R h and NdRhz, have been reported previously. NdRh cryst a l l i z e s w i t h t h e C r B - t y p e s t r u c t u r e , 1 w h i l e NdRhe i s a MgCu2-type Laves phase. 2 T h e s t r u c t u r a l f e a t u r e s of s e v e r a l a l l o y s of n e o d y m i u m a r e s i m i l a r to t h o s e of a n a l o g o u s l a n t h a n u m alloys. However, many instances are known, where the neodymium alloys crystallize with structures d i f f e r e n t f r o m t h o s e of a n a l o g o u s l a n t h a n u m a l l o y s of similar stoichiometry. For example, LaPt has the C r B - t y p e s t r u c t u r e w h i l e N d P t i s of t h e F e B t y p e . 1 LaCu2 i s a n A 1 B 2 - t y p e p h a s e , S ' 4 w h i l e NdCu2 h a s the CeCu2-type structurefl It w a s f e l t t h a t a d e t e r m i n a t i o n of t h e p h a s e e q u i l i b r i a a n d t h e c r y s t a l s t r u c t u r e s of t h e i n t e r m e d i a t e p h a s e s in the N d - R h s y s t e m w o u l d b e b e n e f i c i a l f o r identifying the similarities or differences in the all o y i n g b e h a v i o r s of n e o d y m i u m a n d o t h e r r a r e e a r t h s with rhodium. The results obtained in the Nd-Rh syst e m a r e d e s c r i b e d in t h i s p a p e r a n d a r e c o m p a r e d w i t h those obtained in the La-Rh, s Nd-Co, 6 and Nd-Ni systems. EXPERIMENTAL
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T w e n t y - t w o a l l o y s of v a r y i n g c o m p o s i t i o n s , l i s t e d i n T a b l e I, w e r e p r e p a r e d f r o m Nd, 9 9 . 9 + p c t , a n d R h , 9 9 . 9 2 + p c t , in a c o n v e n t i o n a l a r c f u r n a c e u n d e r a r g o n a t m o s p h e r e in q u a n t i t i e s l e s s t
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