Crystal structure and electrical properties of Tl0.72V6Se6.45P1.55

~)

Solid Stow Communications, Vol. 82, No. 11, pp. 851-855, 1992. Printed in GreatBritain.

0038-1098/9255.00+ .00 Pergamon Press Ltd

CRYSTAL STRUCTURE AND ELECTRICAL PROPERTIES OF T l o . T z V s S e s . 4 m P , . . . W.Bensch, J.Koy I n s t i t u t e for I n o r g a n i c C h e m i s t r y , U n i v e r s i t y of F r a n k f u r t , N i e d e r u r s e l e r Hang, 6 0 0 0 F r a n k f u r t a.M. 50, G e r m a n y and W.Biberacher Walther-Meissner Institute, 8046 Garching, Germany

(Received February 7th, 1992 by P. Wachter, revised April 16th, 1992) Tle.**VsSes.eePt.ne c r y s t a l l i z e s in the h e x a g o n a l Nb3Se4 s t r u c t u r e w i t h T1 a t o m s c o n f i n e d w i t h i n the h e x a g o n a l c h a n n e l s . T h e T1 a t o m s h o w s an u n u s u a l l y h i g h a n i s o t r o p i c d i s p l a c e m e n t c o m p o n e n t U3~ c a u s e d e i t h e r b y s t a t i c d i s o r d e r o r h i g h m o b i l i t y . T h e o b t a i n e d Us3 is c o m p a r a b l e w i t h t h a t f o u n d in the i s o t y p i c c o m p o u n d T I x V e S e . At i00 K the U33 is r e d u c e d b y a b o u t 36 %. T h e P a t o m s are e x c l u s i v e l y d i s t r i b u t e d o n o n e of the t w o p o s s i b l e Se s i t e s a n d a r e in a trig o n a l p r i s m a t i c e n v i r o n m e n t . In c o n t r a s t to the i s o t y p i c T l x V e S 8 the V - V b o n d d i s t a n c e s w i t h i n the z i g - z a g c h a i n s p a r a l l e l to the c r y s t a l l o g r a p h i c c-axis and between these chains are nearly identical. Resistivity measurements perf o r m e d b e t w e e n 300 K a n d 1.5 K e x h i b i t a m e t a l l i c b e h a v i o u r w i t h ~ ( 3 0 0 K ) a b o u t 0.4 m G cm.

Introduction

TII.4V6Se~.eP, but only lattice cons t a n t s w e r e g i v e n t0 . U n f o r t u n a t e l y we w e r e n o t a b l e to p r e p a r e this c o m p o u n d in o u r l a b o r a t o r y . But d u r i n g the e x p e r i m e n t a l w o r k we o b t a i n e d the t i t l e c o m p o u n d in a m i x t u r e w i t h m o n o c l i n i c TlxVsSee-~Pv. Well developed hexagonal s h a p e d s i n g l e c r y s t a l s c o u l d be i s o l a t e d for X - r a y w o r k a n d low t e m p e r a t u r e resistivity measurements. The present contribution deals with the s i n g l e c r y s t a l s t r u c t u r e d e t e r m i n e d at t h r e e d i f f e r e n t t e m p e r a t u r e s as w e l l as w i t h e l e c t r i c a l m e a s u r e m e n t s in the t e m p e r a t u r e r a n g e 1.5 to 300 K.

C o m p o u n d s w i t h the h e x a g o n a l Nb3Se4 s t r u c t u r e a r e of g r e a t i n t e r e s t d u e to their quasi-one-dimensional metallic p r o p e r t i e s *-5 . U n t i l n o w a n u m b e r of d i f f e r e n t c o m p o u n d s w i t h this s t r u c t u r e t y p e h a v e b e e n s y n t h e s i z e d , e.g. T l x T i e S e e 6 , K x T i 3 S 4 7 , T I x V e S e e , AxVeSs • ,t0, A x N b e X e , t , t 2 . M o s t of t h e s e c o m p o u n d s are o n l y c h a r a c t e r i z e d b y Xray diffraction techniques. T h e m e m b e r s of the s e r i e s NbsX4 (X=S,Se,Te) have been investigated e x t e n s i v e l y w i t h r e s p e c t to t h e i r ani s o t r o p i c c o n d u c t i v i t y i,s,4 , s u p e r c o n d u c t i v i t y 1,2 , C D W t r a n s i t i o n a n d m i c r o d o m a i n f o r m a t i o n TM *4. T h e o b s e r v e d p h y s i c a l b e h a v i o u r r e f l e c t s the quasi-one-dimensionality w i t h i n the s e r i e s a n d c a n be e x p l a i n e d w i t h the a i d of e l e c t r o n i c b a n d s t r u c t u r e c a l c u lations*~,xe The second well characterized phase is TlxV, Se in w h i c h the o n e - d i m e n s i o n a l c h a r a c t e r is m a i n t a i n e d e,*7 . It w o u l d be of i n t e r e s t to e x a m i n e w h e t h e r the crystal and physical properties observed in the Nb3X4 s e r i e s a l s o a p p e a r in a hypothetical TlxVsX0 series• Following the s i m p l e a r g u m e n t s of ref *e d e r i v e d from extended H6ckel band structure c a l c u - l a t i o n s for Nb3X4 it s h o u l d be p o s s i b l e to p r e p a r e T l x V s S e e w i t h the Nb3Se4 s t r u c t u r e . S e v e r a l a t t e m p t s h a v e b e e n m a d e to d i r e c t l y s y n t h e s i z e t h i s c o m p o u n d .9 w h i c h w e r e u n s u c c e s s f u l • O h t a n i a n d O n o u e r e p o r t e d the e x i s t e n c e of a c o m p o u n d w i t h the c o m p o s i t i o n

Experimental A m i x t u r e of w e i g h t e d a m o u n t s of T I S e , VP, V3Se4 a n d V S e w a s p l a c e d in a s e a l e d a n d e v a c u a t e d s i l i c a tube. T h e m i x t u r e was s l o w l y h e a t e d to 1273 K a n d h e l d at this t e m p e r a t u r e for 6 days. A f t e r w a r d s the t u b e w a s q u e n c h e d in ice w a t e r . T h e p r o d u c t c o n s i s t s of b l a c k n e e d l e s a n d platelets both with a metallic lustre. T h e X - r a y p o w d e r p a t t e r n c o u l d be i n d e x e d o n the b a s i s of the h e x a g o n a l TlxV6Se8 and monoclinic TlxVsSee structures• Single crystal X-ray investigations w e r e p e r f o r m e d o n a S T O E A E D II d i f f r a c tometer using monochromatized M o K e radiation (~=0.71073 A) e q u i p e d w i t h a c o m m e r c i a l a v a i l a b l e low t e m p e r a t u r e device• T h e a p p r o x i m a t e d i m e n s i o n s of the c r y s tals w e r e 0 . 0 5 x 0 . 0 5 x 0 . 1 5 m m 3 a n d 0 . 0 5 x 0 . 0 5 x 1.5 m m 3 for the c r y s -

851

CRYSTAL STRUCTURE AND ELECTRICAL PROPERTIES

852

tallographic and electrical measurements, respectively. The resistivity a l o n g the c - a x i s was m e a s u r e d w i t h a f o u r p r o b e ac t e c h n i q u e d o w n to 1.5 K. Four gold wires were attached by silver paint yielding a contact resistance b e l o w i0 Q. Results Crystal

structure

and Discussion refinement:

2040 i n t e n s i t y d a t a w e r e c o l l e c t e d o u t to 65 ° 28 w i t h h: 0 -- 14, k: -14 -- 14, i: -5 -- 5 at 2 9 5 K, 200 K a n d i00 K, r e s p e c t i v e l y w i t h the Q - 2 ® s c a n t e c h n i q u e . T h e i n t e n s i t i e s w e r e r e d u c e d to F0 b y a p p l y i n g L o r e n t z , p o l a r i z a t i o n corrections. A numerical absorption correction was performed which signif i c a n t l y r e d u c e d the i n t e r n a l R - v a l u e of the d a t a s e t s . A l l c a l c u l a t i o n s w e r e c a r r i e d o u t in the s p a c e g r o u p P 6 s / m u s i n g the p r o g r a m p a c k a g e S H E L X T L Plus. T h e a t o m i c c o o r d i n a t e s of T I x V 6 S , w e r e t a k e n as s t a r t i n g p a r a m e t e r s . In the f i r s t c y c l e s of i s o t r o p i c r e f i n e m e n t the Se2 a t o m o n the s p e c i a l p o s i t i o n 1/3 2/3 1/4 s h o w e d a h i g h i s o t r o p i c t e m p e r a t u r e p a r a m e t e r Uis0. In the n e x t s t e p the P a t o m w a s p l a c e d at this p o s i t i o n a n d the s i t e o c c u p a t i o n f a c t o r s (SOF) of Se2 a n d P w e r e r e f i n e d w i t h t i e d c o m m o n v a r i a b l e s . A f t e r w a r d s the B O F of T1 w a s d e t e r m i n e d w i t h f r e e l y v a r y i n g S O F a n d U,,0 . T h e S O F of T1 was r e f i n e d to 0 . 0 6 0 ( 2 ) . T h i s p r o c e d u r e r e s u l t e d in the c o m p o s i t i o n T10.v2(2)V6Ses.45(,)P,.~a(,) . During a n i s o t r o p i c c a l c u l a t i o n s the d i s p l a c e m e n t c o m p o n e n t s U,~ of Se2 a n d P were refined with common variables. I m p o r t a n t c r y s t a l d a t a as w e l l as r e f i n e m e n t r e s u l t s are s u m m a r i z e d in T a b l e i. Table

i: c r y s t a l 295

a [A] c [A] V [A'] c/a Z No (>3o(F)) Np x* y2 R [%] wR [96] GOOF 5F [e/A 3] T1 U, 3

data K

9.505(1) 3.413(1) 267.06(9) 0.3591 1 360 19 0.0084(4) 0 . 00002 2.01 1.84 1 • 60 0.76 -0.83 [A'] 0 . 4 1 8 ( 1 0 )

Vol. 82, N o . 11

T h e l a t t i c e c o n s t a n t s are s i g n i f i c a n t l y d i f f e r e n t to t h o s e r e p o r t e d in ref ~° for TII.4V6Se6.aP, ( a = 9 . 5 6 6 a n d c = 3 . 5 1 9 A). B o t h the a- a n d c - a x e s are s i g n i f i c a n t l y s h o r t e r in the t i t l e c o m p o u n d . O n l y s l i g h t c h a n g e s are o b s e r v e d as a f u n c t i o n of t e m p e r a t u r e a c c o u n t i n g for the r i g i d n e s s of the l a t t i c e . The anisotropic displacement p a r a m e t e r (ADP) Usa of the T1 a t o m s h o w s a h i g h v a l u e i n d i c a t i v e for l a r g e t h e r m a l v i b r a t i o n s , s t a t i c d i s o r d e r or h i g h m o b i l i t y . T h e o b t a i n e d Usa is of the s a m e o r d e r as t h o s e o b s e r v e d in the i s o t y p i c c o m p o u n d s T I 0 . s V 6 S a e,17 and Tl0 v a T i 6 S e e 6 . T h e Us3 w a s u s e d to d i s c r i m i n a t e b e t w e e n the t w o p o s s i b l e s p e c i a l zc o o r d i n a t e s 0.0 a n d 0 . 2 5 for TI. For z = 0 . 2 5 the Usa is 0 . 4 1 8 ( 1 0 ) a n d for z = 0 . 0 the Usa r e a c h e s 1 . 8 6 ( 1 6 ) . F u r t h e r more, the d i f f e r e n c e F o u r i e r m a p e x h i b t s l a r g e e l e c t r o n d e n s i t y p e a k s in the position 0,0,0.25. With decreasing t e m p e r a t u r e the Usa is s i g n i f i c a n t l y r e d u c e d a n d y i e l d s 0 . 2 6 6 ( 4 ) at i00 K (compare Fig.l). A c o m p a r i s o n of the c h a n g e of the T1 Usa as a f u n c t i o n of t e m p e r a t u r e w i t h the c h a n g e of the Uil c o m p o n e n t s of the o t h e r a t o m s s u g g e s t s t h a t the d e c r e a s e is m a i n l y d u e to r e d u c e d t h e r m a l m o t i o n . T h e r e f o r e , the h i g h A D P Usa at i00 K is caused by static disorder. Furthermore, the Uil of the o t h e r a t o m s as w e l l as the U** of T1 b e h a v e n o r m a l . T h e s e o b s e r v a t i o n s p o i n t to a o n e - d i m e n s i o n a l d i s o r d e r of the T1 atoms. T h e e n v i r o n m e n t of T1 in 0 , 0 , 0 . 2 5 is i r r e g u l a r w i t h 3 Sel a t o m s at 3 . 0 5 6 ( 1 ) A in a t r i g o n a l p l a n a r c o o r d i n a t i o n a n d a n o t h e r 6 Sel at a d i s t a n c e of 3 . 5 0 1 ( 1 ) A. T h e s h o r t T I - S e l d i s t a n c e is a b o u t 9% s h o r t e r t h a n the s u m of the i o n i c r a d i i (3.38 A), i n d i c a t i v e for h i g h l y c o v a l e n t and refinement 200

K

9.498(1) 3.4088(5) 266.32(9) 0.3589 1 359 19 0.0029(3) 0. 000025 2.08 1.83 i . 94 1.13 -1.07 0.356(7)

results. I00

K

9.484(1) 3.4030(5) 265.09(9) 0.3588 1 354 19 0.0022(3) 0. 000029 2,44 2,15 1 • 79 1.48 -1.34 0.266(4)

I E x t i n c t i o n c o r r e c t i o n c o e f f i c i e n t in F* = F / [ I + 0 . 0 0 2 x F 2 / s i n 20] -I/4 w e i g h t i n g s c h e m e : w = i / ( o z (F) + y F 2 ) No : N u m b e r of o b s e r v e d r e f l e c t i o n s Np : N u m b e r of r e f i n e d p a r a m e t e r s

CRYSTAL STRUCTURE AND ELECTRICAL PROPERTIES

Vol. 82, No. 11

yJ

033 [A"21

0,4

0,3 -

0,2

0,1

0 0

r 50

I 100

I 160

I 200

I 250

300

Temperature [K]

Fig.l The v a r i a t i o n of the U33 with temperature.

of T1

bonds. The T I - S e l bond length shrinks with falling t e m p e r a t u r e (s.Table 2). In p r i n c i p a l two d i f f e r e n t c r y s t a l l o g r a p h i c sites are a v a i l a b l e for the P atom. The r e f i n e m e n t c l e a r l y d e m o n s trates that the P atom e x c l u s i v e l y resides on the special p o s i t i o n -6 in a trigonal p r i s m a t i c environment. In binary p h o s p h i d e s like V2P, VP and VP2 the P atoms are also in a trigonal prismatic e n v i r o n m e n t z°-22 • The V-P bond d i s t a n c e of 2.462(1) A is c o m p a r a b l e with the values r e p o r t e d for the phosphides20 -22 . As can be d e d u c e d from 6 w h i c h is d e f i n e d as the d i f f e r e n c e b e t w e e n the largest and shortest V - P / S e s e p a r a t i o n of 0.168 A the o c t a h e d r a l e n v i r o n m e n t Table

2.

Tl-Sel Tl-Sel V-Sel V-Sel V-Sel V-Se2/P

V-V V-V

about the V atom is s t r o n g l y distorted. But c o m p a r e d with the isotypic sulfide the d i s t o r t i o n is less p r o n o u n c e d (8=0.176 A in the sulfide). It is noted that the V-X bond distances in the title c o m p o u n d are not u n i f o r m l y e n l a r g e d c o m p a r e d with the c o r r e s p o n d i n g V-S bond lengths in the sulfide. This can be d e m o n s t r a t e d by the p e r c e n t a g e i n c r e a s e I(%) of the V - P / S e bond length c o m p a r e d with the corresponding V-S bond d i s t a n c e (see Table 2). As can be seen, the V-P/Se2 s e p a r a t i o n is only s l i g h t l y larger than the V-S2 bond length, whereas the other four d i s t a n c e s are s i g n i f i c a n t l y larger in the title compound. This "inhomogeneous" e n l a r g e m e n t is s c h e m a t i c a l l y shown in Fig.2. With d e c r e a s i n g t e m p e r a t u r e 6 and the average V-Se/P d i s t a n c e s l i g h t l y decrease (compare Table 2). The major feature of the Nb3Se4 s t r u c t u r e type is the q u a s i - o n e - d i m e n s i o n a l i t y of metal zig-zag chains p a r a l l e l to the c r y s t a l l o g r a p h i c . c - a x i s . In the title c o m p o u n d the V-V d i s t a n c e within the chains of 3.057(1) A is only little shorter than b e t w e e n the chains (3.070(1) A). This finding is q u i t e d i f f e r e n t to TlxVsS8 in which the V-V d i s t a n c e b e t w e e n n e i g h b o u r i n g chains is 10% larger than the i n t r a c h a i n distance. The o n e - d i m e n s i o n a l c h a r a c t e r is more p r o n o u n c e d in the Nb3X4 compounds. Here, the d i f f e r e n c e s are 14.5%, 16.8% and 22.9% for X=S,Se,Te, r e s p e c t i v e l y 23.24, 25.

The increase of the i n t r a c h a i n distance b e t w e e n TIxVsS8 and T l x V 6 S e G . 4 S P , . 5 5 is 6.4%, whereas in Nb3S4 and Nb3Se4 the i n t r a c h a i n distances are n e a r l y identical, 2.8813(6) A 23 and 2.885(7) A 24 in the sulfide and selenide, respectively. It is noted that the i n t r a c h a i n d i s t a n c e s i g n i f i c a n t l y d e c r e a s e s with t e m p e r a t u r e whereas the i n t e r c h a i n s e p a r a t i o n remains constant, i.e. the c o m p o u n d becomes more anisotropic with d e c r e a s i n g temperature. This is also o b s e r v e d in TlxV6Se 17 .

I n t e r a t o m i c bond d i s t a n c e s are g i v e n in parentheses.

(A).

Standard

295 K

200 K

i00 K

3x 6x

3.056(1) 3.501(1)

3.052(1) 3.496(I)

3.045(1) 3.488(1)

2x 2x

2.629(1) 2.468(1) 2.500(1) 2.461(1)

2.626(1) 2.467(1) 2.499(1) 2.459(1)

2.622(1) 2.465(1) 2.495(1) 2.456(1)

0.168 2.5032

0.167 2.5015

0.166 2.4982

3.057(1) 3.070(1)

3.051(2) 3.070(1)

3.044(2) 3.068(1)

6 2x 2x

* For e x p l a n a t i o n

see text.

853

deviations

I(%)*

3.91 4.62 6.2 0.16

CRYSTAL STRUCTURE AND ELECTRICAL PROPERTIES

854

Sel

V ~ . 8 2 , No. l l

Electrical properties

)p Sel

\ j

4.6

I

Sel

The room temperature r e s i s t i v i t y along the c-axis amounts to 0.4(1) mQ cm. By cooling down to 1.5 K the res i s t i v i t y d e c r e a s e s m o n o t o n i c a l l y by about 20%. The ~ vs. T curve is displayed in Fig.3. No s u p e r c o n d u c t i n g transition occurs. The small residual resistance ratio R(300K)/R(4.2K) of 1.3 is p r o b a b l y caused by the s t a t i s t i c a l ~ d i s t r i b u t i o n of the P-atoms w h i c h act as s c a t t e r i n g centers. The c r y s t a l l o g r a p h i c finding that the V-V distance within the chains and between the chains is almost identical, suggests a strong r e d u c t i o n of the a n i s o t r o p y of the electrical properties. Because of the tiny crystals we couldn't attack this i n t e r e s t i n g problem. Acknowledgement: Financial support by the D e u t s c h e F o r s c h u n g s g e m e i n s c h a f t DFG is g r a t e f u l l y acknowledged. References

Fig.2 Part of the crystal s t r u c t u r e of T l 0 . T # V s S e s . 4 s P , . s , . O n l y one triple chain of face sharing o c t a h e d r a and one edge sharing o c t a h e d r o n are shown. The numbers r e p r e s e n t the increase of the bond lengths in percent c o m p a r e d with the c o r r e s p o n d i n g bond d i s t a n c e s in the isotypic sulfide. View direction: n e a r l y parallel to the c-axis.

~~

4

-~:'3~ ~-

E o E3 J: _o b > , m

w @

i

50

;

i

I

100 150 200 Temperature IK]

250

300

Fig.3 The v a r i a t i o n of the r e s i s t i v i t y with temperature. The line is the guide for the eye.

1 E . A m b e r g e r , K.Polborn, P.Grimm, M.Dietrich, B.Obst, Solid State Commun. 26, 943 (1978) 2 W.Biberacher, H.Schwenk, Solid State Commun. 33, 385 (1980) 3 Y.Ishihara, I.Nakada, Solid State Commun. 44, 1439 (1982) 4 Y . I s h i h a r a , I . N a k a d a , Solid State Commun. 45, 129 (1983) 5 Y.Ishihara, I.Nakada, K.Suzuki, M.Ichihara, Solid State Commun. 50, 657 (1984) 6 H.Boller, K.Klepp, Mat.Res.Bull. 18, 437 (1983) 7 R.Sch611horn, W.Schramm, D.Fenske, Angew.Chem. 92, 477 (1980) 8 M.Vlasse, L.Fournes, Mat.Res.Bull. ii, 1527 (1976) 9 K.D.Bronsema, G.A.Wiegers, Mat.Res. Bull. 22, 1073 (1987) 10 T.Ohtani, S.Onoue, Mat.Res.Bull. 21, 69 (1986) ii G.Huan, M.Greenblatt, Mat.Res.Bull. 22, 505 (1987) 12 G.Huan, M.Greenblatt, Mat.Res. Bull. 22, 943 (1987) 13 K.Suzuki, M.Ichihara, I.Nakada, Y.Ishihara, Solid State Commun. 59, 291 (1986) 14 K.Suzuki, M.Ichihara, I.Nakada, Y.Ishihara, Solid State Commun. 52, 743 (1984) 15 A.Oshiyama, J.Phys. Soc.Japan 52, 587 (1983) 16 A.Oshiyama, Solid State Commun. 43, 607 (1982) 17 W.Bensch, J.Koy, M.Wesemann, J.Alloys and C o m p o u n d s 178, 193 (1992) 18 E.Canadell, M.H.Whangbo, Inorg.Chem. 25, 1488 (1986) 19 A.Kallel, H.Boller, J . L e s s - c o m m o n Met. 102, 213 (1984) 20 R . B e r g e r , L . - E . T e r g e n i u s , Acta Chem. Scand. A30, 387 (1975)

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CRYSTAL STRUCTURE AND ELECTRICAL PROPERTIES

21 N.Sch6nberg, Acta Chem. Scand. 8, 226 (1954) 22 M.G61in, B.Carlsson, S.Rundqvist, Acta Chem. Scand. A29, 706 (1976) 23 A . F . J . R u y s i n k , F.Kadijk, A.J.Wagner, F.Jellinek, Acta Crystallogr. B24,

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