Critical current densities of hot pressed YBa2Cu3O7−δAg thick film

PI WC

Physiea C 185-189 (1991) 2423-2424 North-Holland

Critical C u r r e n t Densities of Hot Pressed YBa2C%OT.5-Ag Thick Film Terumasa KATO, Noriaki YAMADA and Atsuo IMAI,

Nagoya Municipal Industrial Research Institute, Atsuta-ku, Rokubann 3-chiome 4-41 NAGOYA, 456 JAPAN Composite thick films of YBa2CuaOT.~(YBCO) containing 15wt% Ag have been prepared on partially stabilized zirconia substrates using screen printing and uniaxially pressured sintering. The increase of the sintering pressure decreases the electrical resistance in the normal conductive region and increases the critical current density in the superconductive region. The critical current density was 4.2x104 A/cm 2 at 50K. The YBCO grain size decreased as the sintering pressure increased, The c-axes of YBCO grains oriented preferentially in parallel to the pressure direction. for 5 h ,slowBy cooled to 400°C and kept at that

1,iNTRODUCTION YBa2Ou3OT_s (YBCO) superconductive ceramics

temperature for 5 h ,under continues flow of Oz gas.

have been prepared by a conventional processing

The decomposition of the carbonates was confirmed by

method. But those ceramics have uncontrollable

the disappearance of the endothermb peak due to the

microstructures and insufficient densities for obtaining

decomposition of BaCQ at about 800°C.

high critical current densities(J~)~). Pressure effects on

powder was mixed with

sintering of YBCO ceramics have been investigated by

diisomethyl-acrylate and diisooctyiohth~late

several workers 2'3'4J to improve sintering densities and

an ink. To prepare fiTms , the resulting inks were

microstructures. Those workers reported also sintering

screen-printed onto partially stabilized zirconia (PSZ)

pressure effects on

subst~-ate:~, TWO p," rted substrates were adhered with

the superconductive transition

YBCO

15wt% silver powder, to make

one another on the printed surfaces so as to sandwich

temperature T~. in this report, to increase the critical current density

the

superconductive

thick films

beh~,een both

of superconductive YBazOu3Or.8thick films mixed with

substrates.

s:'.ver powder (YBCO-Ag) were hot pressed with

Y2BaOuO5 around Ag melting temperature. During the

uniaxial pressure.

As the hot pressing pressure

hot pressing process, the samples were kept at 380°C

increases, the critical current density J~ of hot pressed

for 15 h, quickly heated to 980 °C and held for 3 rain.

thick films increases and the c-axis of grains is

to avoid the decomposition of YBCO, and then coo!ed.

oriented parallel to the hot pressing direction.

A~er that, the samples we~e annealed at 400°C in

2oEXPER~E~ENT

flowing O2 gas for 4 h.

Yba2Cu3Oz.sceramic superconductors were prepared

The YBCO starts to decompose into

3oRt~SUL'~S

by solid-state reaction of Y~O3, BaCQ3 and CuO. The

Figure 1 shows the temperature dependencies o,~the

calcining process was repeated at 900°C ,920°C and

critical current density for various sintering pressures.

940°C for 20 h after grinding at each temperature

The resistances at room temperature decreased

=stage until the carbonate of BaCO 3 was decomposed.

linearly

Then the sintered materials were annealed at 800°C

increased with increasing the sisto;ing pressu:e(F O:..~(:

0921-4534/9U$03.50 © 1991 - EUsevier Science Publisl~ccs 9.V.

and the critical current densities J at 507:

All dght,s rescued.

7'. K m o et a L I Critical current densities of hot pressed YBa2CujOT.s-Ag thick film

2424

2). Figure 3 shows the X-ray diffraction patterns of the YBCO thick films hot-pressed at various pressures.

I

i

I01

LlO'A/cm~)

at 50K

The diffraction intensity of the (001) line increases compared with that of (013), (103) and (113) lines. As

R 6~ at 273K

...i "/ "'~

Jc

the hot pressing pressures were increased ,the c-axes of the small YBCO crystals were preferentially oriented perpendicular to the substrate, along the hot pressing axis. We observed diff,, rent microstructures on SEM

--

O

,

,

2

4

,

normally sintered thick film, the length of rectangular

,

8

10

12

•

14

,

16

,

18

20

P (8/cm~)

photographs between the thick film hot pressed at 18g/cm 2 and the normally sintered thick film. For the

,

6

Fig.2 HotpressinQ pressure dependence on resistance at 273K and-critical current density at 50K, of the hot pressed thick films.

shaped grains was about lOpm. On the other hand, the length of rectangular grains of the thick film hoto~ ~

18g/cm 2

oo3 , ~1 ~

13g/cm 2

N

1 lg/cm 2

pressed at 18g/cm ~ is about 2pro and packed densely. 4.Conclusion

•

The effect of pressure on the hot pressed YBCO thick films containing 15% Ag was studied. Hot pressing improve both sintering densities and critical current densities. The best value of the critical current

I

density is 4.2xl0'=Ncm 2 at 50K. The rectangular grain size were decreased with hot pressing pressure, and

O~

~

11S C : ~ / ~ r ~

2

the c-axes of crystals were oriented parallel to the pressure direction. I

,o'AX 5 13

~ ,,o~ ~o

18g/~m2 5

4

Og/cm

I Ig~m21~"

]0

Ag 15%

%

20

50

26)

40

50

50

70

80

Fig.3 X-ray diffraction patternsoof the hQt presse~ thick films at pressure of 0g/cm', 6g/cm', 1 lg/cm, 13g/cm 2 and 18g/cm ~.

Refere.qces 0

50 70 I00 T (K)

1) R.J.Cava etaL:Phys.Rev 36 {1987) 5719. 2) Y.Yamada etat.:Jpn.J.AppI.Phys. 28 (1989) L377.

Fig.1 Critical current density of the hot pressed thick films ~s a function of te~nperature at pressure of Ogicm, 6g/cm, 1 lg/crn and 18glcm-

3) B.P.Singhetat,:Jpn.J,AppLPhys. 26 (1988) L l l 16. 4) G.Bussod eta!.:J,Am.Ceram.Soc. 72 (1989) 137.