Hall effect studies of YBa2Cu3−xFexO7+y

Hall effect studies of YBa2Cu3−xFexO7+y

PhysicaC 162-164 (1989) 1201-1202 North-Hofiand HALL EFFECT STUDIES OF YBa2Cu3_xFexO7+y. G.PRIFTIS*, RATEAU. A.M.GHORAYEB, Laboratoire de Ph...

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PhysicaC 162-164 (1989) 1201-1202 North-Hofiand

HALL

EFFECT

STUDIES

OF

YBa2Cu3_xFexO7+y.

G.PRIFTIS*, RATEAU.

A.M.GHORAYEB,

Laboratoire

de

Physique

O.GOROCHOV,

des

Solides,

R.

SURYANARAYANAN,

CNRS,

92195

Meudon

H.PANKOWSKA

and

M.

France

H a l l d a t a of Y B a 2 C u ~ Fex07+ indicate hole conductivity for O~ x& 0.15. The linear dependence [email protected]~/Rse ~s T d i s a p p e a r s for x "~" 0 . 0 4 . I / R H e follows a regular c u r v e as a f u n c t l o n of T , i d e n t i c a l to t h a t o b s e r v e d ~or undoped samples with varying o x y g e n c o n c ecn t r a t i o n . T h e d a t a m•n d l'c a t e that the relatio n between T and the carrier density is n e a r l y independent of t h e w a y in w h i c h t h e latter isCvaried.

i.

INTRODUCTION

T h e s t u d y of t h e t r a n s p o r t properties of h i g h Tc superconductors has proved the e x i s t e n c e of correlations between parameters such as Ru ( H a l l c o n s t a n t ) , Tc ( t r a n s i t i o n temperature) and the variable composition of o x y g e n or s u b s t i tuted cations ( 1 , 2 ) . On the o t h e r h a n d , the c a s e of Fe s u b s t i t u t e d YBa_Cu_O_ is particularly controversial, theZva~ue of dTc/dx and the orthorhombic-tetragonal transition (O-T) c h a n g e w i t h p r e p a r a t i o n techniques in a l a r g e r a n g e of c o m p o s i tion. There is strong indication that the d T c / d x a n d (O-T) a r e r e l a t e d to the oxygen stoichiometry and therefore to the t h e r m a l treatment (3,4). In t h i s paper, we present R. of YBa~Cu 3 Fe 07 as a function of ~ a n d T. ~e s h ~ w ~ h a ~ Y a c o r r e l a t i o n e x i s t s between 1/Rye and Tc a n d t h a t the l a w of correlatlon seems to be universal for this system as it is i n d e p e n d a n t of t h e w a y in which Tc changes (oxygen stoichiometry or Fe s u b s t i t u t i o n ) . 2.

RESULTS AND DISCUSSION. The ceramic samples were prepared by standard solid state sinterlng. In p a r t i cular, the samples were heated during the f i n a l treatment in o x y g e n at 4 5 0 ° C f o r 50 hours and then c o o l e d to r o o m temperature at 200°C per hour. Tc is defined as the midpoint of the r e s i s tivity transition. The Hall voltage was

* Dept.

Phys.

Univ.

Patras,

Greece.

0921-4534/89/$03.50 © El~vierScien~ Publishe~ B.V. (No.h-Holland)

measured w i t h I=l to l O m A in H = I . I T e s l a u s i n g an ac t e c h n i q u e . The samples studied show a structural (O-T) trasformation for x between 0.07 and 0.i0. For all x, R is p o s i t i v e . I / R H e as a f u n c tion of ~ and x is s h o w n - l n f i g u r e i. The hole density (p = I / R H e in a p p r o x i m a t i o n of a o n e b a n d m o d e l 7 d e c r e a s e s as x increases. Further, the x = 0.01 sample shows a distinct linear dependance on T like the u n d o p e d sample with y 0 to - 0 . 2 . H o w e v e r as x i n c r e a s e s the a v e rage slope dp/dT decreases and a departure from linearity is s e e n . T h e a b o v e results are quite similar to t h o s e o b tained for Ni a n d Co s u b s t i t u t i o n s (5). In a d d i t i o n , this behaviour closely resembles that observed in t h e c a s e of undoped samples but with a variation in oxygen content (7+y) w h i c h is o b t a i n e d by q u e n c h i n g from different temperatures (2, 7). This c a n be u n d e r s t o o d as f o l lows. There is s u f f i c i e n t evidence from X-ray, neutron, MSssbauer and EXAFS data t h a t Fe a t o m s ( f o r s m a l l x) a r e l o c a t e d at Cu 1 s i t e s , t h e ~ as t h e t r i v a l e n t Fe substitutes the Cu L+, an e l e c t r o n compensates a hole resulting in a d e c r e a s e of the h o l e d e n s i t y . It s h o u l d be n o t e d t h a t t h e i n c r e a s e of t h e oxygen content which takes place with the heat treatment at l o w t e m p e r a t u . re w i l l cause the increase of the h o l e concentration and therefore the increase of Tc. d T c / d x = 0 in t h e l i m i t w h e r e the e f f e c t of substitution ( d o p i n g ) by i r o n

G. Priftis et al. / Hall effect studies of YBa2Cu~_~Fe~Oz+y

1202

is c o m p l e t e l y compensated by t h e o x y g e n increase. p as a f(Tc) at 300K a n d 1 0 0 K is s h o w n in fig.2. Also shown are measurements obtained with undoped samples quenched at different temperatures in o r d e r to vary the oxygen content. We infer that the variation o f p as a f ( T c ) is n e a r l y the same for data points obtained at 300 and lOOK. Whatever be the w a y in which the hole density is v a r i e d (doping, heat treatment, non stoiohiometry), all data points are well fitted with a single curve. The maximum value o f Tc is f o u n d to o c c u r f o r a g i v e n h o l e density. Similar results were obtained in t h e case of LaSrCuO (6), Y B a C u O (i), BiSrCaCuO doped and undoped systems (5,8,9,10). One could understand this qualitatively on the basis of a bi-polaron model (ii). At sufficiently low hole density, Tc r i s e s as p i n c r e a s e s . Howev e r , as p increases further the bi-polarons loose stability and hence Tc would decrease rapidly. Other processes may also be possible, and further studies are still needed in t h i s r e s p e c t . Another aspect of the normal state property that is d i f f i c u l t to i n t e r p r e t is t h e linear variation o f p w i t h T. It was pointed o u t t h a t t h i s is a s p e c i f i c property of high Tc superconductors. However, recently it was found that a non-superconductor also exhibits this anomalous behaviour (12). Many two-band models with several restrictions have been proposed to e x p l a i n this behaviour, the most recent of which being that of r e f . 13. In c o n c l u s i o n in Y B a Cu Fe O~ , ' . .. 2 3-x ~ /+y Tc a n d the hole Qensl~y are closely correlated, reEardless of the way in which the hole density is varied. A detailed discussion will be presented elsewhere.

i. 2. 3. 4. 5.

References M.W. S h a f e r et al. P h y s . R e v . , B 39 (1989) 2914 and references therein A.M. Ghorayeb et al. J. L e s s C o m m . Metals, 151 (1989), 221-227 J.M. Tarascon et al. P h y s . R e v . B, 37 13 ( 1 9 8 8 ) 7 4 5 8 - 7 4 6 9 R.Suryanarayanan e t al. J. L e s s C o m m . Metals 151 (1989), 109-114 J. C l a y h o l d et al. P h y s . R e v . B 39

(1989) 6. 7.

8.

J.Clayhold et al. P h y s . R e v . B 39 (1989) 7320 9. M . R a t e a u et al. T h i s c o n f e r e n c e lO.Y.Koike et al. Physica C, 159 (1989) 105 ll.D. Emin et al. Phys. Rev. B 39 (1989) 6575 and references therein 12.Y.Ando et al. Solid S t a t e C o m m . 70 (1989) 303 13.P.M. Eagle Solid State Comm. 69 (1989) 229 and references therein.

2

°o

~

, ~



T(IO2K) Fig. 1 temperature values from 0.04; 0.09;

I/RHe as a function of for Fe doped samples, x t o p to b o t t o m a r e : x = O . 0 2 ; 0.06; 0.07; 0.ii.

6O

40

7324

J.B.Torrance et al. P h y s . R e v . L e t t . , 61 ( 1 9 8 8 ) 1 1 2 7 N.P. Ong et al in Novel Superconductivity (Ed. S . A . W o l f a n d Z.Kresin, Plenum, 1 9 8 7 ) p. 1 0 6 1

2'-0

Fig 2 T vs. I / R H e at 3 0 O K ( m ] a n d a t 100K (0) ~ o r Fe s a m p l e s a n d f o r o x y g e n deficient YBaCuO (0)