The Gd-Yb and Lu-Yb phase systems
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A N D F. H. S P E D D I N G
The Gd-Yb and Lu-Yb phase s y s t e m s were e s t a b l i s h e d by t h e r m a l a n a l y s i s , X - r a y d i f f r a c tion, m e t a l l o g r a p h y , e l e c t r o n m i c r o p r o b e and c h e m i c a l a n a l y s e s . The s o l u b i l i t y of Yb in ~ - G d r a n g e s f r o m 6.5 at. pct at 500~ to 19.0 at. pct at 1161~ The addition of Yb to Gd l o w e r s the fl (bcc) to a (hcp) t r a n s f o r m a t i o n t e m p e r a t u r e to an i n v e r s e p e r i t e c t i c r e a c t i o n at 20.0 at. pct Yb and 1161~ The addition of Yb to Gd lowers the melting point of Gd to a monotectic h o r i z o n t a l at 1183~ which extends f r o m 21.0 to 71.0 at. pct Yb. The monotectic composition is 49.0 at. pct Yb. The solid solubility of Gd in Yb r a n g e s f r o m 0.2 at. pct at 500~ to 2.3 at. pct at 819~ The melting point of Yb is r a i s e d f r o m 816~ to 819~ by the addition of Gd while the r (bcc) to fl (fcc) t r a n s f o r m a t i o n t e m p e r a t u r e of Yb is l o w e r e d f r o m 796~ to 780~ by the addition of Gd. The solubility of Yb in solid Lu r a n g e s f r o m 6.0 at. pct at 800~ to 15 at. pct at 1530~ The addition of Yb to Lu l o w e r s the melting point of Lu to a monotectic horizontal at 1530~ which extends f r o m 15 to 90 at. pct Yb. The monotectic composition is a p p r o x i m a t e l y 30 at. pct Yb. The solid solubility of Lu in Yb r a n g e s f r o m l e s s than 0.1 at. pct at 500~ to 0.3 at. pct at 817~ The addition of Lu r a i s e s the melting point of Yb to 817~ and also r a i s e s the/3 (fcc) to y (bcc) t r a n s f o r m a t i o n t e m p e r a t u r e to 798~ b i n a r y phase s y s t e m s between y t t e r b i u m metal which is n o r m a l l y divalent and the t r i v a l e n t r a r e e a r t h m e t a l s have not been studied e x t e n s i v e l y in the past. A study of the other divalent r a r e e a r t h europium with He and Ce was r e p o r t e d by Savitskii, e t a l . 1 Ytterbium behaves t r i v a l e n t l y in a l a r g e number of compounds--both ionic and t n t e r m e t a l l i c . These r e sults a r e s u m m a r i z e d by Gschneidner 2 who also c a l culated the heat of t r a n s i t i o n from the n o r m a l p l u s two state 3 to the p l u s - t h r e e state of Yb to be 9 k c a l / g . At. In addition to Yb being t r i v a l e n t in a number of int e r m e t a l l t c compounds, the study of the solubility of Yb in Au4 and Pd 5 have indicated Yb e x i s t s in the p l u s t h r e e state when d i s s o l v e d in these m e t a l s . Magnetic studies of Yb d i s s o l v e d in Pds a l s o show it to be t r i valent. In its n o r m a l state Yb metal has only two conduction e l e c t r o n s and has a c o n s i d e r a b l y l a r g e r atomic r a d i u s than the t r i v a l e n t heavy r a r e earth m e t a l s . It has been suggested that the higher e l e c t r o n density of the t r i valent r a r e earth metal might cause a 4f e l e c t r o n in Yb to be p r o m o t e d to the conduction band when Yb is d i
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