Growh and Dielectric Properties of Lead Barium Niobate Single Crystals and Morpeotropic Phase Boundary

Abstract

S i n g l e c r y s t a l s of l e a d bar ium n i o b a t e (PBN) b e l o n g i n g t o t h e t e t r a g o n a l t u n g s t e n b r o n z e s t r u c t u r e s p o s s e s s many d e s i r a b l e p r o p e r t i e s f o r p o t e n t i a 1 a p p l i c a t i o n s i n e 1 e c t r o o p t i c , p i e z o e l e c t r i c a n d p y r o e l e c t r i c d e v i c e s . I n t h e s o l i d s o l u t i o n PbNb206-BaNb206, s u b s t i t u t i o n o f b a r i u m f o r l e a d f i r s t d e c r e a s e s t h e o r t h o r h o m b i c d i s t o r t i o n and l a t e r s t a b i l i z e s t h e t e t r a g o n a l s t r u c t u r e . A morphot ropic phase boundary e x i s t s a t about Pb0.6Ba0.4Nb206. Cur ren t unde r s t and ing based on p h e n o m e n o l o g i c a l c a l c u l a t i o n s o n r e l a t e d m a t e r i a 1 s i n d i c a t e t h a t e 1 e c t r o o p t i c a n d d i e l e c t r i c p r o p e r t i e s o f PBN s h o u l d e x h i b i t c o n s i d e r a b l e e n h a n c e m e n t n e a r t h e m o r p h o t r o p i c p h a s e b o u n d a r y and t h a t t h e y s h o u l d b e l a r g e l y t e m p e r a t u r e i n d e p e n d e n t o v e r a r e a s o n a b l y l a r g e r a n g e o f t e m p e r a t u r e . A s a r e s u l t o f t h i s m o t i v a t i o n , we h a v e grown s i n g l e c r y s t a l s o f PblBaXNb2O6 e m p l o y i n g C z o c h r a l s k i t e c h n i q u e . R e s u f t s o f d i e l e c t r i c c o n s t a n t of two compos i t ions i n t h e o r t h o r h o m b i c s t r u c t u r e w i t h x = 0.37 and 0 . 4 0 a n d one c o m p o s i t i o n i n t h e t e t r a g o n a l s t r u c t u r e w i t h x = 0.65 a r e r e p o r t e d i n t h i s paper. These r e s u l t s l a r g e l y conf i rm t h e p r e d i c t i o n s made by t h e phenomenologica l thermodynamic theory .