Phase diagram of the binary system PbO-Ga2O3

Mat. Res. Bull. Vol. 13, pp. 473-475, 1978. Pergamon Press, Inc. Prhlted in the United States.

l'fi,~S~: ~I,IGR~

OF THE BINARY SYSTEM PbO-Ga20 3

~. N e v P i v a , E° P o l l e r t State Physics, Czech. ~cad. Sci., Czechoslovakia

Institute

o£ S o l i d

Institute

k . I. i s c h e r £or Magnetic ~aterials, Acad° S c i .

Prague,

o£ GDR, J e n a ,

GDR

(Received November 21, 1977; Refereed) ABSTRACT The p h a s e d i a g r a m o£ t h e b i n a r y s y s t e m PbO-Ga203 was d e t e r m i n e d by means o£ eTA and X - r a y m e a s u r e m e n t . The e x i s t e n c e o£ compound £bGa204 i n t h e i n v e s t i g a t e d s y s t e m was c o n £ i r m e d . The compounds Pb2Ga205 and PbGa12019 r e c e n t l y p u b l i s h e d w e r e n o t f o u n d .

Introduction The b i n a r y s y s t e m Pb0-Ga203 h a s n o t b e e n s t u d i e d i n a d e t a i l e d f o r m up t o now. G l a s s e r (1) i n v e s t i g a t e d t h e compounds o£ t h e t y p e ~B204, w h e r e ~ = Pb, Ba, S r , and B = A1, Ga, F e , C r , and p r e p a r e d i n t h i s s e r i e s o£ m a t e r i a l s a l s o t h e compound PbGa204 £ o r whicl~ he s u p p o s e d t h e h e x a g o n a l s t r u c t u r e . Further compound i n t h e s y s t e m PbO-Ga20 3 i s FbGa12019 p r e p a r e d by C h a s s e and W o l t e n (2) as s i n g l e c r y s t a l s £rom P b F 2 - B i 2 0 3 f l u x . They d e t e r m i n e d £ o r t h i s compound t h e m a g n e t R p l u m b i t e - t y p e n structure with lattice p a r a m e t e r s a ffi 5 . 8 2 0 X, c ffi 2 3 . 0 5 6 ~. The c o n d i t i o n s o£ t h e p r e p a r a t i o n and t h e s t a b i l i t y r e g i o n s o£ v a r i o u s compounds i n t h e s y s t e m PbO-Ga203 w e r e i n v e s t i g a t e d G i l l e s ( 3 ) . Me h a s f o u n d i n t h e t e m p e r a t u r e r e g i o n 6000 - ~ 0 0 b u c t h e compound Pb2Ga205 w i t h c u b i c s t r u c t u r e ( a = 1 3 . 4 6 A) and d e t e r m i n e d t h e f o r m a t i o n t e m p e r a t u r e o£ PbGa204 a t 800 °C having orthorhombic structure (pro~able space group P 222 ) with lattice p a r a m e t e r s a = 9 . 4 1 5 X, b = 5 . 2 1 6 ~, c = 8 . 5 8 5 ~. G i l l e s was n o t s u c c e s s £ u l t o p r e p a r e PbGa12019 compound by t h e solid state reaction. The p r e s e n t i n v e s t i g a t i o n has been devoted m i n a t i o n o£ t h e Pb0-Ga203 p h a s e d i a g r a m . 473

to t h e d e t e r -

474

M. NEV~tIVA, et ~ .

Vol. 13, No. 5

Experimental ~art

Preparation

o£ Samples

The s p e c t r o s c o p i c p u r e C~-Ga203 ( J o h n s o n - M a t h e y ) and y e l l o w Pb0 p . a . ( L a c h e m a Brno) as s t a r t i n g m a t e r i a l s were u s e d . T h e i r c o m p o s i t i o n was t e s t e d by c h e m i c a l a n a l y s i s . The s t a r t i n g m i x t u r e s w e r e p r e p a r e d by h o m o g e n i z a t i o n o£ Pb0 and Ga203 weighted in required ratios. Two s e r i e s o£ p e l l e t s w e r e p r e s s e d from t h e h o m o g e n i z e d m i x t u r e s ( p e l l e t s a b o u t 5 mm i n d i a m e t e r 3 mm t h i c k and p e l l e t s a b o u t 10 mm i n d i a m e t e r b mm t h i c k ) . The £ i r s t s e r i e s o£ s m a l l e r p e l l e t s was u s e d £ o r DTA m e a s u r e m e n t s . The p e l l e t s o£ t h e s e c o n d s e r i e s w e r e £ i r e d a t v a r i o u s t e m p e ratures. I h e h e a t i n g o f t h e s a m p l e s above t h e o u t e c t i c t e m p e r a t u r e ( c o m p o s i t i o n 0 - 50 mol~ Ga203) a n d / o r above t h e p e r i t e c t i c t e m p e r a t u r e ( c o m p o s i t i o n 50 - 100 mol% Ga203) r e s p e c t i v e l y was done s i m u i t a n e u u s l y i n a i r and i n t h e c l o s e d s i l i c a t u b e s . The pellets heated in silica tubes were f i r s t wrapped in p l a t i n u m f o i l to p r e v e n t t h e i r c o m i n g i n t o c o n t a c t w i t h s i l i c a g l a s s . Below t h e s e t e m p e r a t u r e s t h e s a m p l e s w e r e h e a t e d i n a i r . P e l l e t s p r e £ i r e d a t d e s i r e d t e m p e r a t u r e w e r e r e g r o u n d p r e s s e d and a g a i n £ i r e d . T h i s p r o c e d u r e was r e p e a t e d u n t i l t h e e q u i l i b r i u m s t a t e was r e a c h e d . The t o t a l t i m e o£ h e a t i n g d i d n o t e x c e e d 50 h o u r s f o r £ i r i n g a bove t h e e u t e c t i c a n d / o r p e r i t e c t i c temperatures respectively and i 5 0 h o u r s £ o r £ i r i n g b e l o w t h o s e temperatures. DTA M e a s u r e m e n t s A c o m m e r c i a l a p p a r a t u s N e t z s c h e q u i p p e d by DD K -measu rin g h e a d w i t h p l a t i n u m c r u c i b l e s as s p e c i m e n h o l d e r s was u s e d . The t e m p e r a t u r e was m e a s u r e d by i n d e p e n d e n t P t - P t R h l 0 t h e r m o c o u p l e calibrated by ICTA s t a n d a r d s . The t e m p e r a t u r e d i £ f e r e n c e AT was i n d i c a t e d by a d i f £ e r e n t i a i Pt-PtRhl0 thermocouple with sensitivity 0 , 0 5 mY/25 cm, e . g . 0 . 3 3 K/cm a t i 3 0 0 K. The h e a t i n g r a t e f o r t h e e n t i r e m e a s u r e m e n t s was 10 K / m i n . X-Ray Analysis

The p h a s e s c o m p o s i t i o n o£ t h e s a m p l e s o£ tile s e c o n d s e r i e s was d e t e r m i n e d by t h e X - r a y d i £ £ r a c t i o n a n a l y s i s . The m e a s u r e m e n t s w e r e done by means o£ X - r a y d i £ f r a c t o m e t e r bl{0N-i. The CuKC~ r a d i a t i o n £ i l t e r e d by n i c k e l £ i l t e r was e m p l o y e d .

Results and discussion

The p h a s e d i a g r a m o f t h e s y s t e m PbO-Ga~O 3 c o n s t r u c t e d on t h e b a s i s o£ DT~ and X - r a y m e a s u r e m e n t s i s gmven i n t h e F i g u r e . One eutectic at 18.5 mot% Ga203 and temperature 728 °C was found in the system by D T ~ m e t h o d . By the same method the liquidus curves in the temperature region 728 - 1110 °C were determined. The DTA measurement supplied the peritectic melting p o i n t 0£ t h e compound PbGa204 a t 885 °C i n c o n t r a r y to t h a t one (825 °C) £ o l l o w i n g ~rom t h e X - r a y a n a l y s i s o£ t h e q u e n c h e d s a m p l e s . The l a t t e r v a l u e ~ s e e m s t o be p r o b a b l y more c r e d i b l e . The r e s u l t s o£ LTA c a n be i n £ 1 u e n c e d by t h e n o n - e q u i l i b r i u m

Vol. 13, No. 5

THE SYSTEM PbO-Ga203

475

conditions following from the comparable rates o£ PbGa204 d e composition a n d o£ t h e h e a t i n g r a t e u s e O a t t h e DTA m e a s u r e ment. Below the eutectic temperature o n l y PbO a n d PbGa203 p h a ses coexist, in the composition r e g i o n 0 - 50 m o l t G a 2 0 3 . T h e existence o£ t h e c o m p o u n d P b 2 G a 2 0 5 p r e v i o u s l y reported by G i l les (3) was not confirmed.

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FIG. 1 Phase oiagram of the system PbO-Ga203 + results o f DTA m e a s u r e m e n t s , " PbO*PbGa204, o FbGa204, A PbGa240 + Ga2O3, • Ga203 ( h e a t e d i n a n d / o r P b 0 + Ga203 ( h e a t e d i n s e a l e d silica tubes, see text).

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~any experiments were done in order to prepare the exp e c t e d P b G a 1 2 0 1 9 c o m p o u n d . The s t a r t i n g mixtures containing 50 - 90 m o l t Ga2Q 3 w e r e h e a t e d i n a i r i n t h e t e m p e r a t u r e reg i o n 8 5 0 - ~ 4 0 0 vC a n d / o r i n s e a l e d s i l i c a tubes at temperature 840 - 1050 C. The X - r a y a n d c h e m i c a l a n a l y s i s o£ t h e s a m p l e s

476

M. NEVI~IVA, et ~ .

Vol. 13, No. 5

h e a t e d i n a i r o n l y s h o w e d t h e p r e s e n c e o£ Ga203 p h a s e w h i l e PbO was e v a p o r a t e d . 1£ t h e e v a p o r a t i o n was s u p p r e s s e d by t h e u s e o f t h e s e a l e d s i l i c a t u b e s , t h e n b o t h Ga203 and PbO w e r e d e t e c t e d a£ter the equilibrium treatments. Also t h e a t t e m p t s to p r e p a r e t h e s i n g l e c r y s t a l s o£ PbGa12019 £rom PbO £ I u x were n o t s u c c e s s £ u l . The g r o w i n g r u n s l e d i n e v e r y c a s e t o Ga203 c r y s t a l s . S i m i l a r l y , C h a s s e and • o l t e n (2) d i d n o t o b t a i n p u r e PbGa12019 b u t o n l y c r y s t a l s o£ t h i s t y p e c o n t a i n i n g t r a c e s o f l a n t h a n u m as t h e c o n s e q u e n c e o£ t h e s t a r t i n g c o m p o s i t i o n o£ t h e m e l t (20 Ga203, 2~ B i 2 0 3 , 57 PbF 2 and 1 L a 2 0 3 ) . We c o n c l u d e f r o m our s t u d y t h a t p u r e m a g n e t o p l u m b i t e p h a s e PbGa12019 i s ~ p p a r e n t l y n o t t h e r m o d y n a m i c a l l y s t a b l e i n the investigated temperature region.

Acknowledgements The a u t h o r s a r e i n d e b t e d to e x p r e s s t h e i r g r a t i t u d e t o Mrs. E. Hrub~ and Mrs. R. E u l e r £ o r t e c h n i c a l a s s i s t a n c e and t o I n g . A. Nov~k f o r c h e m i c a l a n a l y s i s .

Re~erences

1. F. ~. G l a s s e r 377 ( 1 9 6 3 ) .

and L. 5.

Dent G l a s s e r ,

2 . ,~. B. C h a s s e and G. M. W o l t e n , J . (1965). 3.

J . C. G i l l e s ,

J.

Amer. C e r . ~oc. 4_~6,

~mer. C e r . S o c . 48, 276

Compt. Rend. S 6 r . C 2 7 1 ,

61 ( 1 9 7 0 ) .