Phase and High-Temperature Thermodynamic Studies in the Lutetium

16 Phase and High-Temperature Thermodynamic

Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch016

Studies in the Lutetium-Sulfur System HUGO

F.

FRANZEN

and

ALLEPPEY

V.

HARIHARAN

Ames Laboratory, DOE and Department of Chemistry, Iowa State University, Ames, I A 50011

The

lutetium-sulfur

the

extended

mediate

phase(s),

homogeneity

and

range

investigated of

derived

sublattice,

cubic

determine inter-

properties.

monosulfide

extends

line phase, Lu3S4,

identified

between

homogeneity

thermodynamic

vaporizing

to

monosulfide,

from the parent face-centered

was

high-temperature

the

thermodynamic

of the

end of the monosulfide gruently

was

A new intermediate

LuS0.75—LuS1.30.

a superstructure (fccub)

system

nonstoichiometry

Lu3S4

the 2

and LuS are

with cubic

sulfur-rich

range and Lu S3. properties

The from

of

the

The con-

reported.

n p h e l a n t h a n i d e monosulfides, e x c e p t S m S , E u S , a n d Y b S , e x h i b i t n o n stoichiometry

towards

metal-rich compositions.

The

homogeneity

r a n g e extends d o w n to a c o m p o s i t i o n c o r r e s p o n d i n g to LuSo.75 f o r y t t r i u m a n d t h e h e a v y l a n t h a n i d e s ; this r a n g e lanthanides

is m u c h s m a l l e r f o r the l i g h t

L u t e t i u m monosulfide

(1,2,3,4).

is u n i q u e

i n that

the

n o n s t o i c h i o m e t r i c c o m p o s i t i o n extends s i g n i f i c a n t l y to the m e t a l - r i c h a n d s u l f u r - r i c h regions w h i l e m a i n t a i n i n g t h e f c c u b r o c k salt s t r u c t u r e . the hyperstoichiometry of the monosulfide, c h e m i s t r y of c h a l c o g e n i d e s , those of s c a n d i u m .

In

a n d i n the general crystal

l u t e t i u m c o m p o u n d s t e n d to b e s i m i l a r to

T h e p h a s e a n d h i g h - t e m p e r a t u r e b e h a v i o r of

the

L u - S system w a s of interest e s p e c i a l l y i n v i e w of t h e o b s e r v a t i o n t h a t i n t h e S c - S system the c o n g r u e n t l y v a p o r i z i n g c o m p o s i t i o n is ScSi. 4 2

T h e p u r p o s e of nonstoichiometry

(5).

the present s t u d y w a s to e s t a b l i s h the extent

of

of L u S , i d e n t i f y i n t e r m e d i a t e a n d t e r m i n a l p h a s e ( s )

a n d the c o n g r u e n t l y v a p o r i z i n g c o m p o s i t i o n , a n d o b t a i n p e r t i n e n t t h e r m o d y n a m i c d a t a i n the system. 0-8412-0472-1 /80/33-186-309$05.00/l ©

1980

A m e r i c a n C h e m i c a l Society

Holt et al.; Solid State Chemistry: A Contemporary Overview Advances in Chemistry; American Chemical Society: Washington, DC, 1980.

310

SOLID S T A T E

CHEMISTRY:

A

CONTEMPORARY

OVERVIEW

Phase Studies L u t e t i u m sulfides i n the c o m p o s i t i o n r a n g e of S / L u 0.6-1.5 w e r e s y n t h e s i z e d b y the d i r e c t c o m b i n a t i o n of the elements c o n t a i n e d i n o u t gassed, e v a c u a t e d , a n d sealed q u a r t z tubes at 8 7 0 ° C .

The

as-reacted

materials w e r e s u b s e q u e n t l y h o m o g e n i z e d at 1500°C i n t u n g s t e n c r u c i b l e s i n h i g h v a c u u m . S i n c e the w e i g h t losses of the samples d u r i n g h o m o g e n i zation were negligible, the

final

product compositions

were

t a k e n as

essentially the same as the i n i t i a l c o m p o s i t i o n s . X - r a y d i f f r a c t i o n patterns Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch016

of the p o w d e r e d samples w e r e o b t a i n e d i n a H a g g - t y p e G u i n i e r c a m e r a ( r a d i u s 50 m m ; C u K « i r a d i a t i o n ; s i l i c o n i n t e r n a l s t a n d a r d ) . T h e homogeneity LuSo.75-LuSi.3o.

The

r a n g e of l u t e t i u m m o n o s u l f i d e is e s t a b l i s h e d as cubic

l a t t i c e p a r a m e t e r increases

sharply from

5 . 3 1 6 ( 1 ) A at L U S O . T I ( i n e q u i l i b r i u m w i t h L u m e t a l ) to 5.356(1) A at L u S i . 0 3 a n d thereafter less r a p i d l y to 5 . 3 6 4 ( 1 ) A at L u S i . 2 9 ( F i g u r e 1 ) . T h e t r e n d i n the l a t t i c e p a r a m e t e r i n d i c a t e s that the e x t e n d e d h o m o g e n e i t y results f r o m the presence of r a n d o m v a c a n c i e s i n the s u l f u r a n d l u t e t i u m sublattices, r e s p e c t i v e l y , o n e i t h e r side of t h e t r u e m o n o s u l f i d e c o m p o s i t i o n . T h e l a t t i c e p a r a m e t e r of s t o i c h i o m e t r i c L u S i . o is i n t e r p o l a t e d to 5.355(1) A . T h e c o m p o s i t i o n S / L u = hedral-hexagonal: a =

6.722(2) A ; c =

0.8 Figure 1.

1.5 forms p u r e L u S 2

3

[rhombo-

18.141(7) A ] .

1.0 S/Lu

Cubic cell lattice parameters (±0.001 position

A) of LuS

x

versus com-


16.

FRANZEN

A N D

Lutetium-Sulfur

HARIHARAN

311

System

A significant r e s u l t of this s t u d y is the i d e n t i f i c a t i o n of a n e w i n t e r m e d i a t e l i n e p h a s e , L u S , b e t w e e n the s u l f u r - r i c h e n d of t h e m o n o s u l f i d e 3

4

homogeneity range a n d L u S . 2

3

T h e s t r u c t u r e of L u S , t e n t a t i v e l y estab 3

4

l i s h e d f r o m t h e G u i n i e r p o w d e r d i f f r a c t i o n , is c l o s e l y r e l a t e d to the d e f e c t Sc S 2

type (6)

3

a n d is a s u p e r s t r u c t u r e d e r i v e d f r o m t h e p a r e n t f c c u b

s u b l a t t i c e . T h e s u l f u r l a t t i c e is c o m p l e t e l y

filled,

a n d vacancies occur i n

t h e c a t i o n s u b l a t t i c e sites ( o r d e r e d i n t h e case of t h e S c S s t r u c t u r e t y p e 2

but partly occupied i n L u S ) . 3

4

3

A s u b s t r u c t u r e of t h e c o m p o u n d is o r t h o -


r h o m b i c , space g r o u p F d d d , w i t h a — 1 0 . 7 6 4 ( 3 ) A ; b =

7.708(3) A ;

2 2 . 8 6 1 ( 8 ) A . S i n g l e - c r y s t a l refinement of the s t r u c t u r e is i n progress.

c =

X - r a y p h o t o e l e c t r o n s p e c t r a of l u t e t i u m sulfide c o m p o s i t i o n s L u S . 8 0

L u S i . , L u S , and L u S 2

3

4

2

h a v e also b e e n s t u d i e d ( 7 ) .

3

T h e most significant

i n f o r m a t i o n a b o u t t h e c a t i o n - a n i o n i n t e r a c t i o n i n these c o m p o u n d s o b t a i n e d f r o m the S 2 p b i n d i n g energies. LuS .8-LuSi. 0

T h i s v a l u e , 162.7 ±

is

0.2 e V i n

a n d L u S , is v e r y close to t h e b i n d i n g e n e r g y i n n e u t r a l

2

3

sulfur, whereas i n L u S 2

4

3

i t is a p p r e c i a b l y s h i f t e d , to 161.8 e V , t y p i c a l of

r e l a t i v e l y i o n i c sulfides. T h e d a t a i n d i c a t e v e r y l o w c h a r g e transfer f r o m the m e t a l to s u l f u r , or, a l t e r n a t i v e l y , a p p r e c i a b l e b a c k b o n d i n g f r o m the a n i o n to t h e m e t a l i n t h e n o n s t o i c h i o m e t r i c monosulfides a n d t h e s t r u c turally related L u S , w h i l e i n L u S 3

4

2

conventional ionic b o n d i n g becomes

3

p r e d o m i n a n t . T h e L u 4 d c o r e - b i n d i n g energies also s h o w a p a r a l l e l t r e n d i n these c o m p o u n d s .

Thermodynamic

Studies

T h e i n t e r m e d i a t e p h a s e , L u S , is e s t a b l i s h e d as t h e 3

congruently

4

v a p o r i z i n g c o m p o s i t i o n i n the L u - S system at h i g h t e m p e r a t u r e .

The

v a p o r i z a t i o n of this p h a s e w a s s t u d i e d b y mass s p e c t r o m e t r i c a n d t a r g e t c o l l e c t i o n K n u d s e n effusion t e c h n i q u e s i n t h e t e m p e r a t u r e r a n g e of 1 9 2 7 2216 K . L u S 3

4

v a p o r i z e s a c c o r d i n g to

L u S i . » ( s ) == L u ( g ) + 8

LuSi.

8 8

(s) =

L u S (g) +

F r o m t h e slopes of t h e l o g I T versus ( 1 / T )

1.338(g)

(1)

0.33S (g)

(2)

data for L u a n d L u S vapor

species, a n d a c o r r e s p o n d i n g slope f o r s u l f u r gas consistent w i t h c o n g r u e n c y of t h e v a p o r i z a t i o n reactions ( 1 )

e n e r g y of L u S ( g ) is c o m p u t e d as D ° [ L u S ( g ) = 0

120.6 ±

the

a n d ( 2 ) , the dissociation Lu(g)

+

S(g)]

=

3.2 k c a l • m o l ' . T h e effusion d a t a h a v e b e e n r e d u c e d to o b t a i n 1

the f o l l o w i n g s e c o n d - l a w t h e r m o d y n a m i c v a l u e s ( e u represents e n t r o p y unit):


312

SOLID

STATE

Reaction (1):

CHEMISTRY:

A f f ° 298 AS°

A S ° 298 ;

CONTEMPORARY OVERVIEW

317.6 ± 2.3 k c a l 79.6 ± 1.1 eu

298

R e a c t i o n ( 2 ) : &H° 298

A

196.9 db 3.1 k c a l 55.9 ± 1.5 e u

These thermal data, appropriately combined, yield, for the condensed phase, S° 98

[LuSi.

2


LuSi.33, A H ° 8 8

f

f

(*)] =

2

98

[LuSi. (s)] = 3 3

18.0 ±

- 1 2 6 . 5 ± 2.3 k c a l • m o l "

1

and

1.1 e u .

T h e m o n o p h a s i c c o m p o s i t i o n s LuS0.75-LuS1.30 d e c o m p o s e o n h e a t i n g i n v a c u u m w i t h loss of L u a n d e v e n t u a l l y f o r m L u S . 3

I n order to

4

c a l c u l a t e the t h e r m o d y n a m i c p r o p e r t i e s o f s t o i c h i o m e t r i c l u t e t i u m m o n o sulfide, L u S i . o , t h e a c t i v i t y o f L u i n t h e c u b i c p h a s e r e g i o n w a s m e a s u r e d at 2026 K b y the K n u d s e n effusion m e t h o d . G i b b s - D u h e m i n t e g r a t i o n o f the d a t a y i e l d e d the a c t i v i t y o f s u l f u r across t h e single-phase r e g i o n w i t h respect to t h e c o n g r u e n t l y v a p o r i z i n g c o m p o s i t i o n o f L u S . 3

combined

data the following

thermodynamic

values

4

F r o m the

f o r LuSi.o are

calculated: A n a t o m i z a t i o n , 298

[ L u S (s) — L u (g) + S (g) ]

A # S u b l i m a t i o n , 298

—

268.5 ± 3.0 k c a l • m o l '

[LuS(s) = L u S ( g ) ] =

147.7 ± 3.0 k c a l • m o l '

Afl

r o

f >

298

[LuS(s)]

99.6 ± 3.1 k c a l • m o l

1

1

- 1

Glossary of Symbols fccub = face-centered c u b i c T = temperature i n kelvin I = +

mass s p e c t r o m e t r i c i o n i n t e n s i t y ( a r b i t r a r y u n i t s )

e u = e n t r o p y u n i t , calories p e r degree p e r m o l e (s) = solid ( g ) — gas D°

= dissociation energy

8

A H ° 2 9 8 = s t a n d a r d e n t h a l p y c h a n g e at 298 K A S ° 2 9 8 — s t a n d a r d e n t r o p y c h a n g e at 298 K AH°

f

)

2

= s t a n d a r d e n t h a l p y o f f o r m a t i o n at 298 K

98

S ° 2 9 8 = s t a n d a r d e n t r o p y at 298 K Acknowledgment T h i s w o r k w a s s u p p o r t e d b y the U . S . D e p a r t m e n t o f E n e r g y , Office of B a s i c E n e r g y Sciences, M a t e r i a l s Sciences D i v i s i o n . Literature

Cited

1. Flahaut, J.; Laruelle, P. "Progress in the Science and Technololgy of the Rare Earths"; Eyring, L., Ed.; Pergamon: New York, 1968; Vol. 3, p. 149.


16.

F R A N Z E N

A N D

HARIHARAN

Lutetium-Sulfur

System

313

2. Flahaut, J.; Guittard, M . ; Gonchov, O.; Winterberger, M . In "Proprietes Thermodynamiques, Physiques et Structurales des Derives Semimetalliques"; Collogue Orsay: Paris, 1967; No. 157, p. 431. 3. Bruzzone, G.; Olcese, G. L. In "Properties Thermodynamiques, Physiques of Structurales des Derives Semimetalliques"; Colloque Orsay: Paris, 1967; No. 157, p. 387. 4. Guittard, M. Compt. Rend. 1965, 261, 2109. 5. Tuenge, R . T.; Laabs, F.; Franzen, H . F. J. Chem. Phys. 1976, 65, 2400. 6. Dismukes, J. P.; White, J. G. Inorg. Chem. 1964, 3, 1220. 7. Franzen, H. F.; Hariharan, A. V. J. Solid State Chem. 1978, 26, 189. Downloaded by UNIV OF SOUTHERN CALIFORNIA on June 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1980 | doi: 10.1021/ba-1970-0186.ch016

RECEIVED September 13, 1978.


Phase and High-Temperature Thermodynamic Studies in the Lutetium

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