Cation self diffusion in titanium monoxide
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Table I. Properties of the TiO x Ingots
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T. S. LUNDY, R. A. P A D G E T T , AND M. D. BANUS T H E high t e m p e r a t u r e s o l id m o n o x i d e of t i t a n i u m has a cubic NaC1 c r y s t a l s t r u c t u r e that is s t a b l e o v e r v e r y wide r a n g e s of t e m p e r a t u r e and s t o i c h i o m e t r y . The v a c a n c y c o n c e n t r a t i o n s m e a s u r e d a f t e r q u e n c h i ng s p e c i m e n s f r o m high t e m p e r a t u r e s for both the anion and cation s u b l a t t i c e s v a r y m a r k e d l y with s t o i c h i o m e t r y f r o m a low for cation v a c a n c i e s of n e a r 6 pct at x = 0.75 in TiOx to a high of n e a r 24 pct at x = 1.3. The phase f i e l d e x i s t s under e q u i l i b r i u m conditions at one a t m o s s p h e r e p r e s s u r e above about 450~ w i t h a n e v e r - w i d e n ing s t o i c h i o m e t r i c r a n g e a s the t e m p e r a t u r e is i n c r e a s e d to the e u t e c t i c at about 1700~ Nonstoichiometric specim e n s m a y be q u e n c h e d f r o m a b o v e 1000~ to r e t a i n the NaC1 s t r u c t u r e but TiO1.0 r e a d i l y f o r m s an o r d e r e d , l o w t e m p e r a t u r e m o n o c l i n i c p h a s e below 950~ Considerable i n f o r m a t i o n r e g a r d i n g s t r u c t u r a l , c h e m i c a l , p h y s i c a l , and e l e c t r i c a l p r o p e r t i e s for the cubic m o n o x i d e of t i t a n i u m has been p u b li s h e d 1 but t h e r e is no p r e v i o u s i n f o r m a t i o n r e g a r d i n g e i t h e r s e l f or i m p u r i t y diffusion processes. This paper reports a cursory examination of cation s e l f diffusion in this s y s t e m . F o u r s m a l l c y l i n d r i c a l ingots of TiOx about 8 m m in d i a m e t e r w e r e p r e p a r e d by t e c h n i q u e s p r e v i o u s l y d e scribed. ~ Stoichiometries, lattice parameters, densities, and q u e n c h e d - i n anion and cation v a c a n c y c o n c e n t r a t i o n s for t h e s e ingots a r e l i s t e d in T a b l e I. The l a t t i c e p a r a m e t e r is a s e n s i t i v e function of s t o i c h i o m e t r y and w as used to so c h a r a c t e r i z e the m a t e r i a l . T h e g r a i n s i z e of all the m a t e r i a l w a s quite l a r g e , in the r a n g e of 0.1 to 2.0 m m d i a m . The ingots w e r e cut into s p e c i m e n s about 3 m m thick by use of a d i a m o n d - i m p r e g n a t e d w i r e saw. The two ingots n e a r TiO~.o w e r e b r i t t l e - - p r o b a b l y due to t h e i r p a r tial t r a n s f o r m a t i o n d u r i n g quenching to the m o n o c l i n i c pha s e c o n f i r m e d by X - r a y d i f f r a c t i o n . One face of each s p e c i m e n was p o l i s h e d th r o u g h 4 / 0 e m e r y p a p e r and then a s m a l l quantity of solution containing 44Ti w as dr o p p ed onto the p r e p a r e d s u r f a c e and e v a p o r a t e d to d r y n e s s . S p e c i m e n s of the four s t o i c h i o m e t r i e s w e r e s t a c k e d a l t e r n a t e l y with tung
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