Phase diagram of the Bi 2 O 3 -SrO-CaO quasiternary system

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agreement with those in the available phase diagram,°] w h i c h were determined by differential thermal analysis and high-temperature X-ray diffraction. Although some samples prepared at 1166 K with compositions near 55 tool pct BiO~5 gave different results from those in the available phase diagram,i7] it was found that the phases in the samples did not change during cooling or r e m o v a l from the furnace. Roth e t al.[8] have claimed in their structural research that those compounds o f Bi6Ca7016 and Bi~0CavO22 proposed by Conflant e t a / .17] should be expressed as Bi2Ca205 and Bi6Ca4Oj3, respectively. In this work, though two phases o f Bi6Ca7Ol6 and BiloCaTO22 were detected in the samples with a molar composition ratio o f B i : C a = 1: 1 and the single phase o f Bi6fa7Ol6 was observed in a region between B i : C a = 4 6 : 5 4 and B i : C a = 4 7 : 5 3 , a single phase was detected in some samples with a molar composition ratio o f B i : C a = 3:2 in accordance with the result o f Roth e t a l . Consequently, in this study, the expression o f Bi10CaTO22 by Conflant e t a l . has been employed, because the difference between the molar composition ratios o f B i : C a = 10:7 and B i : C a = 3:2 is small. Table II shows the experimental results o f the relationships between initial molar composition ratios o f B i : S r : Ca and the determined phases at 973 K. The mole fractions were calculated for the constituents o f BiO~ 5, SrO, and CaO. The experiments were conducted mainly in the region with BiOn5 contents from about 40 to 80 tool pct with more than 100 samples of different compositions. The observed isothermal section o f the phase d i a g r a m at 973 K is shown in Figure 1. The characteristics o f the result are that a solid solution n a m e d 6 is present in a wide composition range with BiO~.5 contents o f about 50 mol pct BiO~5 and that the 6 phase is in two-phase equilibrium with one o f seven phases o f CaO, Bi6fa7Oi6, Bi10CaTO22 ' ]3,15 8] Bi2SrO4, BizSr2Os, and Bi3Sr4Ca3Oin 5. These phases o f BimCaTO22 and Bi2Sr609 were also confirmed to be solid solutions w h i c h can be more generally expressed as BiloSrxCa7 xO22 and Bi2Sr6_xCaxO9, respectively.

~7~o,~

973K

'":i\ °°° '

/

QI¢ \

I

\BiloCa7022

," / / I N-/ I / Bi:]sr4Ca3Oll5 /I KI. I /5,30

!

/ / \

,

1"

Bi2Sr,,sOgA/v

v

v

80

70

60

BI2SrzvOs' 50

)

, BizSrO4 40

30

/3 v 20

"

"'ca'°'' ~o x

,, / /

\

10 B i O l . 5

---- mol% SrO

Fig. 1--Isothermal section of the BiO~ 5-SrO-CaO system at 973 K. VOLUME 24A, JUNE 1993--1447

T a b l e I.

Experimental

At 1052 K Bi:Ca 30:70 40:60 46:54 47:53 At 1099 K Bi:Ca 30:70 40:60 47:53 50:50 At 1166 K Bi:Ca 30:70 40:60

R e s u l t s o n the Relations b e t w e e n M o l a r C o m p o s i t i o n R a t i o of B i : C a and D e t e r m i n e d P h a s e s

Phases

Bi:Ca

Phases

Bi:Ca

Phases

Bi:Ca

Phases

p + CaO p + CaO p p

50:50 55:45 59:41 60:40

p + m p + m m + p* m

62:38 65:35 67:33 70:30

m + b m + b b b + ~

71:29 72:28 77:23 80:20

b + a a + b*

Phases

Bi:Ca

Phases

Bi:C

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