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Electronic properties of YBa2Cu3O6.85 compound
PhysicaC 153-155 (1988) 1337-1338 North-Holland, Amsterdam
ELECTRONIC PROPERTIESOF YBa2Cu306.85 COMPOUND C. SULKOWSKI, K. ROGACKI, Z. BUKOWSKI, R. HORYNand E. TROJNAR I n s t i t u t e for Low Temperature and Structure Research, Polish Academy of Sciences, Pr6chnika 95, 53-529 Wroclaw, Poland Superconducting t r a n s i t i o n t~perature Tc , r e s i s t i v i t y p , thermopower S, and l a t t i c e parameters have been measured for f i v e samples of YBa2Cu307_A where the oxygen concentration changes between 6.83 - 6.90 only. The Tc's of the samples are almost the same and equal to 91 K (+l K), however, large differences in values of the p (0.74-1.7 m~cm) and the S (-1.6 ÷ +5.9 uV/K) at 300 K as well as clear correl a t i o n between these parameters have been observed. We suppose, the differences are coused by ordering of the heavy ions i n the u n i t cell rather than changes of the oxygen concentration. Growth of the ordering leads to observed decreasing of u n i t cell volume and reduction of the r e s i s t i v i t y and thermopower. The compound YBa2Cu307_Z~demonstrates clearly metallic character, high superconducting transition temperature Tc and orthorhombic structure at oxygen concentration above 6.5 . The Tc depends on oxygen index, although parameter (b-a)/(b+a), (where a,b - l a t t i c e parameters) seems define better this relation (1). For the value of A
The r e s i s t i v i t y p decreases l i n e a r l y with the temperature in the range from 300 K to 140 K and i t f a l l s rapidly at lower temperatures. Such run of the r e s i s t i v i t y was observed for a l l samples, however values of the p were d i f f e r e n t and varied from 0.74 m~cm to 1.7 m~cm at 300 K, similar to values of the r e s i s t i v i t y ratio P300 K/PIO0 K , which varied from 3.2 to 2.1 , respectively. Internal structure influence of these sintered samples upon p was not considered. The thermoelectric power S was measured by placing the sample between two copper blocks. Copper wires were attached to the two-block-sample interfaces carried the thermoelectric voltage signal to a d i g i t a l voltmeter. On the each block a copper wire thermometer and a heater were reeled. In this way the temperatures of the blocks and the difference of the temperatures were determined. Sizes of the samples used in the measurements were: the length 2÷ 5 mm , the area of cross section 0 . 5 ÷ I . 5 mm2. The accuracy of this thermoelectric power measurements was about 15%. The temperature dependences of the thermopower S for our samples are presented in Fig. I. The absolute S values are rather low, l i k e for metals. For sample 5, which has the lowest r e s i s t i v i t y (0.74 m~cm at 300 K), and the highest P3QOK/PIO0 K ratio (3.2),the S value is negative. Clear correlation between the thermopower S and the r e s i s t i v i t y p have been observed. These plots are presented in Fig. 2 at two temperatures: 300 K and lO0 K. These results on thermopower are similar to those obtained for samples with comparable oxygen con:centra~on but a f t e r d i f f e r e n t thermal treatment ( 3 , 4 , 5 , 6 ) . For our samples, with oxygen contents changing in the range of the error of measurements, any c o r r e l a t i o n s between S or p values and oxygen concentration could not be found. However, a
C. Sulkowski et aL / Electronic properties of YBa 2Cu306.85 compound
1338
8
S 6
~IV/K 4 2 0 -2 6O
100
1~
'tSO
20
260
300
T, K - - - FIGURE l Temperature dependences of the thermoelectric power S for f i v e samples with composition near YBa2Cu306.85 •
t
proportionality of S to the u n i t cell volume occurs and can be interesting. The u n i t cell volume for our samples changes only of about 1% and may be the result of ordering of the heavy ions (Ba, Y, Cu) in the l a t t i c e ; the growth of the ordering effects the decrease of the u n i t cell volume. We suppose, that this ordering is a reason for essential changes of a band structure of the compound, what can le~ad even to a change of the thermopower sign. For samples from l to 4 the sign is positive, confirming that the hole conduction dominates, but for the sample 5 i t is negative and therefore the electron conduction can be important. In conclusion, we may state that samples of the high Tc superconductor with composition near YBa2Cu307 , which were thermal treatment at s l i g h t l y d~fferent conditions can show the same Tc's but very d i f f e r e n t transport properties. I t seems to be caused by differences in the ordering of the heavy ions rather than by changes of the oxygen concentration. REFERENCES (1)
(2)
0
(3)
8
S
V/K
f/ o
:/"
0.3
0.6
0.9
9,
(5)
(6)
:
-2
(4)
1.2
1.5
m~cm . - - - -
FIGURE 2 Thermoelectric power S versus r e s i s t i v i t y p, for two indicated temperatures.
Z. Bukowski, R. Hory~, K. Rogacki, I. Fi}atow, C. Su}kowski, M. Wo}cyrz and J. Klamut, submitted to J. Less-Common Met. S. Uchida, Proc. YSC '87 on Superconducti v i t y in Highly Correlated Systems, Sendai. Z. Henkie, R. Horyn, Z. Bukowski, P.j. Markowski and J. Klamut, Solid State Commun. 64 (1987) 1285. U. Gottwick, R. Held, G. Sparn, F. Steglich, H. Rietschel, D. Ewert, B. Renker, W. Bauhofer, S. von Molnar, M. Wilhelm and H.E. Hoening, Europhys. Lett. 4 (1987)I183. V. Bayot, F. Delannay, C. Dewitte, J-P. Erauw, X. Gonze, J-P. I s s i , A. Jonas, M. Kinany-Alaoui, M. Lambricht, J-P. Michenaud, J-P. Minet and L. Piraux, Solid State Commun. 63 (1987) 983. Z. Henkie, P.J. Markowski, R. Horyh, Z. Bukowski and J. Klamut, phys. stat. sol. (b), in p r i n t .
ELECTRONIC PROPERTIESOF YBa2Cu306.85 COMPOUND C. SULKOWSKI, K. ROGACKI, Z. BUKOWSKI, R. HORYNand E. TROJNAR I n s t i t u t e for Low Temperature and Structure Research, Polish Academy of Sciences, Pr6chnika 95, 53-529 Wroclaw, Poland Superconducting t r a n s i t i o n t~perature Tc , r e s i s t i v i t y p , thermopower S, and l a t t i c e parameters have been measured for f i v e samples of YBa2Cu307_A where the oxygen concentration changes between 6.83 - 6.90 only. The Tc's of the samples are almost the same and equal to 91 K (+l K), however, large differences in values of the p (0.74-1.7 m~cm) and the S (-1.6 ÷ +5.9 uV/K) at 300 K as well as clear correl a t i o n between these parameters have been observed. We suppose, the differences are coused by ordering of the heavy ions i n the u n i t cell rather than changes of the oxygen concentration. Growth of the ordering leads to observed decreasing of u n i t cell volume and reduction of the r e s i s t i v i t y and thermopower. The compound YBa2Cu307_Z~demonstrates clearly metallic character, high superconducting transition temperature Tc and orthorhombic structure at oxygen concentration above 6.5 . The Tc depends on oxygen index, although parameter (b-a)/(b+a), (where a,b - l a t t i c e parameters) seems define better this relation (1). For the value of A
The r e s i s t i v i t y p decreases l i n e a r l y with the temperature in the range from 300 K to 140 K and i t f a l l s rapidly at lower temperatures. Such run of the r e s i s t i v i t y was observed for a l l samples, however values of the p were d i f f e r e n t and varied from 0.74 m~cm to 1.7 m~cm at 300 K, similar to values of the r e s i s t i v i t y ratio P300 K/PIO0 K , which varied from 3.2 to 2.1 , respectively. Internal structure influence of these sintered samples upon p was not considered. The thermoelectric power S was measured by placing the sample between two copper blocks. Copper wires were attached to the two-block-sample interfaces carried the thermoelectric voltage signal to a d i g i t a l voltmeter. On the each block a copper wire thermometer and a heater were reeled. In this way the temperatures of the blocks and the difference of the temperatures were determined. Sizes of the samples used in the measurements were: the length 2÷ 5 mm , the area of cross section 0 . 5 ÷ I . 5 mm2. The accuracy of this thermoelectric power measurements was about 15%. The temperature dependences of the thermopower S for our samples are presented in Fig. I. The absolute S values are rather low, l i k e for metals. For sample 5, which has the lowest r e s i s t i v i t y (0.74 m~cm at 300 K), and the highest P3QOK/PIO0 K ratio (3.2),the S value is negative. Clear correlation between the thermopower S and the r e s i s t i v i t y p have been observed. These plots are presented in Fig. 2 at two temperatures: 300 K and lO0 K. These results on thermopower are similar to those obtained for samples with comparable oxygen con:centra~on but a f t e r d i f f e r e n t thermal treatment ( 3 , 4 , 5 , 6 ) . For our samples, with oxygen contents changing in the range of the error of measurements, any c o r r e l a t i o n s between S or p values and oxygen concentration could not be found. However, a
C. Sulkowski et aL / Electronic properties of YBa 2Cu306.85 compound
1338
8
S 6
~IV/K 4 2 0 -2 6O
100
1~
'tSO
20
260
300
T, K - - - FIGURE l Temperature dependences of the thermoelectric power S for f i v e samples with composition near YBa2Cu306.85 •
t
proportionality of S to the u n i t cell volume occurs and can be interesting. The u n i t cell volume for our samples changes only of about 1% and may be the result of ordering of the heavy ions (Ba, Y, Cu) in the l a t t i c e ; the growth of the ordering effects the decrease of the u n i t cell volume. We suppose, that this ordering is a reason for essential changes of a band structure of the compound, what can le~ad even to a change of the thermopower sign. For samples from l to 4 the sign is positive, confirming that the hole conduction dominates, but for the sample 5 i t is negative and therefore the electron conduction can be important. In conclusion, we may state that samples of the high Tc superconductor with composition near YBa2Cu307 , which were thermal treatment at s l i g h t l y d~fferent conditions can show the same Tc's but very d i f f e r e n t transport properties. I t seems to be caused by differences in the ordering of the heavy ions rather than by changes of the oxygen concentration. REFERENCES (1)
(2)
0
(3)
8
S
V/K
f/ o
:/"
0.3
0.6
0.9
9,
(5)
(6)
:
-2
(4)
1.2
1.5
m~cm . - - - -
FIGURE 2 Thermoelectric power S versus r e s i s t i v i t y p, for two indicated temperatures.
Z. Bukowski, R. Hory~, K. Rogacki, I. Fi}atow, C. Su}kowski, M. Wo}cyrz and J. Klamut, submitted to J. Less-Common Met. S. Uchida, Proc. YSC '87 on Superconducti v i t y in Highly Correlated Systems, Sendai. Z. Henkie, R. Horyn, Z. Bukowski, P.j. Markowski and J. Klamut, Solid State Commun. 64 (1987) 1285. U. Gottwick, R. Held, G. Sparn, F. Steglich, H. Rietschel, D. Ewert, B. Renker, W. Bauhofer, S. von Molnar, M. Wilhelm and H.E. Hoening, Europhys. Lett. 4 (1987)I183. V. Bayot, F. Delannay, C. Dewitte, J-P. Erauw, X. Gonze, J-P. I s s i , A. Jonas, M. Kinany-Alaoui, M. Lambricht, J-P. Michenaud, J-P. Minet and L. Piraux, Solid State Commun. 63 (1987) 983. Z. Henkie, P.J. Markowski, R. Horyh, Z. Bukowski and J. Klamut, phys. stat. sol. (b), in p r i n t .