Electrical resistivity of V-H alloys
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The e l e c t r i c a l r e s i s t i v i t y h a s b e e n d e t e r m i n e d at t e m p e r a t u r e s b e t w e e n 120 ~ and 500~ for V-H a l l o y s with h y d r o g e n c o n c e n t r a t i o n s f r o m 0 to 42.1 at. pct. A plot of the h y d r o g e n s o l u b i l i t y l i m i t in v a n a d i u m shows that it i n c r e a s e s f r o m 0.5 at. pct at 227~ to 26.4 at. pct at 436~ X - r a y d i f f r a c t i o n powder p a t t e r n s i n d i c a t e d that a l l o y s c o n t a i n i n g b e t w e e n 33.8 a n d 42.1 at. pct H w e r e s i n g l e - p h a s e , b c t , ~ - V h y d r i d e at r o o m t e m p e r a t u r e . The r e s i s t i v i t y of the 33.8 a t . pct a l l o y c l o s e l y a p p r o x i m a t e d that of h y d r o g e n - f r e e v a n a d i u m , but the r o o m t e m p e r a t u r e r e s i s t i v i t y i n c r e a s e d with i n c r e a s i n g h y d r o g e n c o n c e n t r a t i o n at the r a t e of 1.7 m i c r o h m - c m p e r at. pct H. T h e s e ~ a l l o y s underwent one t r a n s f o r m a t i o n at t e m p e r a t u r e s b e l o w 224~ and two m o r e t r a n s f o r m a t i o n s n e a r 450~ The r a t i o n a l e h a s b e e n b a s e d on i n c r e a s i n g d i s o r d e r of h y d r o g e n in the i n t e r s t i c e s of the l a t t i c e with i n c r e a s i n g t e m p e r a t u r e .
MAELAND 1 has p r e s e n t e d a t e n t a t i v e phase d i a g r a m for the V-H s y s t e m . F o r h y d r o g e n c o n c e n t r a t i o n s b e tween 31.5 and 42.9 a t . pct h i s X - r a y p a t t e r n s i n d i c a t e d the e x i s t e n c e of only ~ p h a s e , b c t v a n a d i u m h y d r i d e a t r o o m t e m p e r a t u r e . The p r e s e n t i n v e s t i g a t i o n e x t e n d s e a r l i e r w o r k z on the r e s i s t i v i t y of V - H a l l o y s to include h y d r o g e n c o n c e n t r a t i o n s f r o m 0 to 42.1 at. p c t and, t h e r e f o r e , i n c l u d e s w o r k on t h e s e /3-phase a l l o y s . E X P E R I M E N T A L PROCEDURE The m a t e r i a l , a p p a r a t u s , and technique w e r e d e s c r i b e d e a r l i e r . ~ The p r e s e n t study included h i g h e r t e m p e r a t u r e s so the s p e c i m e n was i m m e r s e d in Dow C o m i n g diffusion pump oil 703 b e t w e e n 300 ~ and 500~
v a l u e s of ao for t h e s e a l l o y s a r e 2.999, 3.009, and 3.028~, r e s p e c t i v e l y , which m a k e s t h e m v i r t u a l l y i d e n t i c a l to the v a l u e s found by M a e l a n d . The v a l u e s of Co w e r e 3.311, 3.324, and 3.355~, r e s p e c t i v e l y , only s l i g h t l y l o w e r than M a e l a n d ' s v a l u e s a n d s l i g h t l y h i g h e r than those in Ref. 3. A t y p i c a l p h o t o m i c r o g r a p h of the s u b s t r u c t u r e in ~ - V h y d r i d e i s shown in F i g . 3. The r e s i s t i v i t y of t h e s e p o l y c r y s t a l l i n e a l l o y s i n c r e a s e s with i n c r e a s i n g h y d r o g e n c o n c e n t r a t i o n at 300~ a s shown in F i g . 4. The i n
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