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Effects of annealing on electrical properties of oxygen-deficient YBa2Cu3Ox
Physica C 235-240 (1994) 1453-1454 North-Holland
PHYSICA
Effects of annealing on electrical properties of oxygen-deficient YBa2Cu3Ox S. Edoa and T. Takamab aDepartment of Mechanical System Technology, ttokkaido Polytechnic College, Zenibako 3-190, Otaru 047-02, Japan. bDepartment of Applied Physics, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan. Thermal stability of the physical properties in oxygen-deficient YBa2Cu30 x has been investigated. Measurements of dc resistivity showed that metal to semiconductor transition takes place during annealing at temperatures up to 300 °C. Diamagnetic magnetization remarkably decreased with an increase in annealing temperature. 'rids indicates that the volume fraction of superconducting phase diminishes with temperature. The electrical transition accompanies a structural change to tetragonal-like phase which is thought to have the semiconducting nature.
1. INTRODUCTION It has been established that oxygendeficient YBa2Cu3Ox has the two different superconducing phases with T~= 90 and 60 K depending on the oxygen concentration. The crystal structure varies from orthorhombic to tetragonal with a decrease in oxygen concentration x [1-3]. Although the oxygendeficient sample is thought to be in nonequilibrium state at room temperature, the detailed studies for thermal stability have not been performed. In the present study, it is shown that electrical properties are unstable for the heat-treatmt~ t at relatively low temperature.
2. EXPERIMENTAL The compounds were synthesized by the solid-state reaction method at 940°C in air using Y203, BaCO3 and CuO powders. In order to prepare the samples with valious oxygen concentrations, the samples were annealed at the temperatures between 550 and 925 °C in air and quenched into liquid nitrogen. Oxygen concentration was determined by thermogravimetry (TG). The resistivity was measured in air during
thermal cycles between room temperatm'e and 750 °C. Each quenched sample was annealed at temperatures up to 300 °C for l0 hours in air and in argon gas atmospheres. The dc resistivity and the ac magnetic susceptibility below room temperature were measured for annealed samples by means of the four-probe and the Hartshon methods, i espectively. Xray diffraction were taken to cheek the crystal structure.
3. R E S U L T S AND DISCUSSION Figure 1 shows the resistivity as a fmmtion of temperature, As the temperatau'e is increased, the resistivity shows an anomalous increase with ~;wo pe:~1 at around 250 and 300 °C. Weight ~ rage ~ 1 .~ 4-1.,.~,,.,T~.n measureu• b y - mI~_T revea,eu ~,,c,~ t h ~,~ ,-,-c,~---. concentration is preserved uiJ, to 300 °C. The di'op in resistivity above 300 °C is due to oxygen absorption. The influence of the annealing on resistivity is shown in Fig. 2. Resistivity at room temperature increases with an hmrease in annealing temperatawe. The negative slope of the resistivity indicates that the metal to semiconductor transition takes
0921-4534D4/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)01290-3
1454
S. Edo, T, Takama/Physica C 235-240 (1994) 1453-1454
in Fig. 1. The decrease in the magnetization corresponds to the decrease in a volume fraction of the superconducting phase. Judging from the resistivity and the magnetization, the rest portion is thought to transform to semiconductor. The increase in the volume fraction of the semiconducting phase should alter the resistive To.
3.0 2,5
E C~ 2,0
~ O.5
/
0.0
..~
200
400 600 Tcmpcr,aturc (*C)
t.o
800
v !
Figure 1. Temperature dependence resistivity at higher temperatures.
1.2
of
o
0.8
0.6
,~,,,
~ 0.4
i.~
....
@---°--
•
= 0.2 ~0
o.o
2.5-
.
I
.
t
__1
,
I00 200 300 Annealing Temperature (°C)
2.O
400
Figure. 3. Magnetization at 10 K as a function of annealing temperature.
1.5 "~
300 °C 0.5
o.o _ _ b
6
..............................
50
15o
2oo
aso
300
Temperature (K) Figure 2. Temperature dependence of resistivity at lower temperatures for different heat treatments. The oxygen concentration x of the sample is 6.4.
X-ray diffraction patterns revealed that the change in the electric state coincides with the staazctural change from the orthorhombic to a tetragonal-like structure by annealing. Taking account of the two conducting phases, tetragonal-like phase is thought to be responsible for the semiconducting nature. It is concluded that the physical properties of oxygen-deficient YBa2CusOx is thermally unstable. REFERENCES
place during the annealing. The superconducting transition temperature Tc fluctuates by the annealing. Magnetic To, however, did not show the annealing temperature dependence. The diamagnetic magnetization at 10 K is dra~aa in Fig. 3. In comparison with the as-quenched sample, the magnetization at 250 °C decreases by about 70 %. The temperature of 250 °C corresponds to that of the let~ peak in the resistivity curve shown
1. R. J. Cava, B. Batlogg, C. H. Chen, E. A. Rietman, S. M. Zahurak and D. Werder, Phys. Rev. B, 36 (1987) 5719. 2. W. Wong-Ng, L. P. Cook, C. K. Chiang, L. ar~zenttruDer, ~. ft. t~elmett, J. BlendeU and D. Minor, J. Mater. Res., 3 (1988) 832 3. J. D. Jorgensen, B. W. Veal, A. P. Patdfl~as, L. J. Nowicki, G. W. Crabtree, H. Claus and W. K. Kwok, Phys. Rev. B, 41 (1990 ) 1863. Z.
~ w
•
~
1
PHYSICA
Effects of annealing on electrical properties of oxygen-deficient YBa2Cu3Ox S. Edoa and T. Takamab aDepartment of Mechanical System Technology, ttokkaido Polytechnic College, Zenibako 3-190, Otaru 047-02, Japan. bDepartment of Applied Physics, Faculty of Engineering, Hokkaido University, Kita-ku, Sapporo 060, Japan. Thermal stability of the physical properties in oxygen-deficient YBa2Cu30 x has been investigated. Measurements of dc resistivity showed that metal to semiconductor transition takes place during annealing at temperatures up to 300 °C. Diamagnetic magnetization remarkably decreased with an increase in annealing temperature. 'rids indicates that the volume fraction of superconducting phase diminishes with temperature. The electrical transition accompanies a structural change to tetragonal-like phase which is thought to have the semiconducting nature.
1. INTRODUCTION It has been established that oxygendeficient YBa2Cu3Ox has the two different superconducing phases with T~= 90 and 60 K depending on the oxygen concentration. The crystal structure varies from orthorhombic to tetragonal with a decrease in oxygen concentration x [1-3]. Although the oxygendeficient sample is thought to be in nonequilibrium state at room temperature, the detailed studies for thermal stability have not been performed. In the present study, it is shown that electrical properties are unstable for the heat-treatmt~ t at relatively low temperature.
2. EXPERIMENTAL The compounds were synthesized by the solid-state reaction method at 940°C in air using Y203, BaCO3 and CuO powders. In order to prepare the samples with valious oxygen concentrations, the samples were annealed at the temperatures between 550 and 925 °C in air and quenched into liquid nitrogen. Oxygen concentration was determined by thermogravimetry (TG). The resistivity was measured in air during
thermal cycles between room temperatm'e and 750 °C. Each quenched sample was annealed at temperatures up to 300 °C for l0 hours in air and in argon gas atmospheres. The dc resistivity and the ac magnetic susceptibility below room temperature were measured for annealed samples by means of the four-probe and the Hartshon methods, i espectively. Xray diffraction were taken to cheek the crystal structure.
3. R E S U L T S AND DISCUSSION Figure 1 shows the resistivity as a fmmtion of temperature, As the temperatau'e is increased, the resistivity shows an anomalous increase with ~;wo pe:~1 at around 250 and 300 °C. Weight ~ rage ~ 1 .~ 4-1.,.~,,.,T~.n measureu• b y - mI~_T revea,eu ~,,c,~ t h ~,~ ,-,-c,~---. concentration is preserved uiJ, to 300 °C. The di'op in resistivity above 300 °C is due to oxygen absorption. The influence of the annealing on resistivity is shown in Fig. 2. Resistivity at room temperature increases with an hmrease in annealing temperatawe. The negative slope of the resistivity indicates that the metal to semiconductor transition takes
0921-4534D4/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)01290-3
1454
S. Edo, T, Takama/Physica C 235-240 (1994) 1453-1454
in Fig. 1. The decrease in the magnetization corresponds to the decrease in a volume fraction of the superconducting phase. Judging from the resistivity and the magnetization, the rest portion is thought to transform to semiconductor. The increase in the volume fraction of the semiconducting phase should alter the resistive To.
3.0 2,5
E C~ 2,0
~ O.5
/
0.0
..~
200
400 600 Tcmpcr,aturc (*C)
t.o
800
v !
Figure 1. Temperature dependence resistivity at higher temperatures.
1.2
of
o
0.8
0.6
,~,,,
~ 0.4
i.~
....
@---°--
•
= 0.2 ~0
o.o
2.5-
.
I
.
t
__1
,
I00 200 300 Annealing Temperature (°C)
2.O
400
Figure. 3. Magnetization at 10 K as a function of annealing temperature.
1.5 "~
300 °C 0.5
o.o _ _ b
6
..............................
50
15o
2oo
aso
300
Temperature (K) Figure 2. Temperature dependence of resistivity at lower temperatures for different heat treatments. The oxygen concentration x of the sample is 6.4.
X-ray diffraction patterns revealed that the change in the electric state coincides with the staazctural change from the orthorhombic to a tetragonal-like structure by annealing. Taking account of the two conducting phases, tetragonal-like phase is thought to be responsible for the semiconducting nature. It is concluded that the physical properties of oxygen-deficient YBa2CusOx is thermally unstable. REFERENCES
place during the annealing. The superconducting transition temperature Tc fluctuates by the annealing. Magnetic To, however, did not show the annealing temperature dependence. The diamagnetic magnetization at 10 K is dra~aa in Fig. 3. In comparison with the as-quenched sample, the magnetization at 250 °C decreases by about 70 %. The temperature of 250 °C corresponds to that of the let~ peak in the resistivity curve shown
1. R. J. Cava, B. Batlogg, C. H. Chen, E. A. Rietman, S. M. Zahurak and D. Werder, Phys. Rev. B, 36 (1987) 5719. 2. W. Wong-Ng, L. P. Cook, C. K. Chiang, L. ar~zenttruDer, ~. ft. t~elmett, J. BlendeU and D. Minor, J. Mater. Res., 3 (1988) 832 3. J. D. Jorgensen, B. W. Veal, A. P. Patdfl~as, L. J. Nowicki, G. W. Crabtree, H. Claus and W. K. Kwok, Phys. Rev. B, 41 (1990 ) 1863. Z.
~ w
•
~
1