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Physico-chemical regularities of high-Tc superconducting materials synthesis
PhysicaC 153-155 (1988) 1663-1664 North-Holland, Amsterdam
PHYSICO-CHE~ICAL REGULARITIES OF HIGH-T c SUPERCONDUCTING MATERIALS SYNTHESIS A.B.Blank, V.T. Zagoskin, L.A.Kvichko, L.A.Kotok, Yu.G.Litvinenko, V.P.Seminozhenko "Monokristallreaktiv" association, Kharkov, USSR Optimum conditions for the synthesis of LnBa2Cu307_ x and LnBa2_xSrxCU307_ x ceramics, where Ln~La, Y, Yb, Tm, Gd have been found. The synthesis and decomposition processes are multistageous. The superconducting Y-Ba-Cu-O ceramics with density 6 glcm 3 has been prepared by hot pressing of powders. The LnBa2Cu30y samples, where Ln-Y, Yb, Tm, Gd, were prepared through solid state reaction of the initial compounds taken in the stoichiometric ratio with subsequent sintering. Nitrates of the rare earths (RE), Cu, Ba, oxides of RE, Ou and barium compounds - BaC03, BaO, BaO 2 were used as initial raw material~ TG curves of all the systems show the weight loss in the temperature range of 840-116500. The observed exoeffect at 81000 on the DTA curves corresponds to the BaCO 3 modification transformation 11/ whereas endoeffects in the range of 965-985°C bear evidence of a step-wise character of the superconducting phase formation process through some intermediate compounds of BaCuO 2 (I) and Ln2BaCuO 5 (II) type.Endoeffects at 1010-1030°0 existing in all the systems except Gd - one are due to the superconducting phase (I-2-3) decomposition. The presence o~ the sintering threshold temperature (Tth) above which there begins 1-2-3 phase decomposition has been observed(Pig.1$. Tth for Tm and Y was 925 and 950 °C respectively. The decomposition mechanism of the superconducting phase proceeds in the same way in all the systems - through 0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
the intermediate compounds I and II to simple oxides.
,L/to 3 2
0 -t -2 -3 .4
FIGURE I "Expansion-compression curves for LnBa2Ou3Oy. I - TmBa2Ou3Oy; 2 GdBa2Cu3Oy; 3 - YBa2OU3Oy; 4 YbBa2Ou3Oy. The highest YBa20U30y samples densities (6.09 g/cm 3) were obtained by hot pressing of the mixture containing 95 % of the superconducting phase at 800Oc and under the pressure of 750 MPa (Fig.2). The conditions for the preparation of the ceramics with the composition YBa2.xSrCu30y have been developed for x = 0.5; I; O; 1.5; 1.75. It has been found that during heat
1664
A.B. Blank et aL / Physico-chemical regularities
treatment in the argon flow there takes place I-2-3 phase decomposition followed by the oxygen loss (by a factor of 1.3) with Ba1_xSrxCuO 2 formation on the background of
phase which
one can observe the needles of STY204 and Y2Ba1_xSrxCuO 5 phases (electron probe microanalysis, X-ray analysis).
6.0 58 56
c ,IY°Y 70/0
0
5,2 $0
°c
An anomalous shape of the temperature curve of the electric resistance was observed for the compositions with x=1.5 (the drop of for more than an order at 180 K) and with x = = 1.75. However, this effect has poor reproducibility. Partial substitution of Y for Cr and Ti (Yo.8Cro.2Ba2Cu30y and Yo.8Tio.2Ba2Cu3Oy) deteriorates the superconducting properties and the stability of the ceramics. The application of the mentioned results allowed to develop the stable process for the preparation of the ceramics with the reproducible properties: samples density - 95 %; T c = = 93-100 K; ~ T = I-2 K; I c = IO3A/cm 2 at 77 K.
4% 44
42
FIGURE 2 Hot-pressed ceramics density dependence upon temperature and pressure. The subsequent thermal treatment in oxygen leads to the reduction of I-2-3 phase and to the increase of the oxygen content bound to copper. A small amount of other phases remains. T c for this composition is 78-80 K. It has been found that for
REFERENCES
/I/ V.P.SemSnozhenko et al, Physicochemical and analytical control for the preparation of the ceramics with the preset properties. Dokl. Akad. Nauk Uk. SSR (in Russian), 1987, N 11. /2/ T.Woda, S.Adachi, T.~ihara, R.Inaba, S~bstitution effect of Sr for
Y21~2_xSrxCu30y samples thermally
Ba of high-T c
treated in the ambient air (x
YBa2Cu307_y ceramics. Jap. J. Appl° Phys. 26 (1987) pp.L706L708.
1.5)
the increase of x results in T c and lattice parameters decrease,as in /2/.
superconducting
PHYSICO-CHE~ICAL REGULARITIES OF HIGH-T c SUPERCONDUCTING MATERIALS SYNTHESIS A.B.Blank, V.T. Zagoskin, L.A.Kvichko, L.A.Kotok, Yu.G.Litvinenko, V.P.Seminozhenko "Monokristallreaktiv" association, Kharkov, USSR Optimum conditions for the synthesis of LnBa2Cu307_ x and LnBa2_xSrxCU307_ x ceramics, where Ln~La, Y, Yb, Tm, Gd have been found. The synthesis and decomposition processes are multistageous. The superconducting Y-Ba-Cu-O ceramics with density 6 glcm 3 has been prepared by hot pressing of powders. The LnBa2Cu30y samples, where Ln-Y, Yb, Tm, Gd, were prepared through solid state reaction of the initial compounds taken in the stoichiometric ratio with subsequent sintering. Nitrates of the rare earths (RE), Cu, Ba, oxides of RE, Ou and barium compounds - BaC03, BaO, BaO 2 were used as initial raw material~ TG curves of all the systems show the weight loss in the temperature range of 840-116500. The observed exoeffect at 81000 on the DTA curves corresponds to the BaCO 3 modification transformation 11/ whereas endoeffects in the range of 965-985°C bear evidence of a step-wise character of the superconducting phase formation process through some intermediate compounds of BaCuO 2 (I) and Ln2BaCuO 5 (II) type.Endoeffects at 1010-1030°0 existing in all the systems except Gd - one are due to the superconducting phase (I-2-3) decomposition. The presence o~ the sintering threshold temperature (Tth) above which there begins 1-2-3 phase decomposition has been observed(Pig.1$. Tth for Tm and Y was 925 and 950 °C respectively. The decomposition mechanism of the superconducting phase proceeds in the same way in all the systems - through 0921-4534/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
the intermediate compounds I and II to simple oxides.
,L/to 3 2
0 -t -2 -3 .4
FIGURE I "Expansion-compression curves for LnBa2Ou3Oy. I - TmBa2Ou3Oy; 2 GdBa2Cu3Oy; 3 - YBa2OU3Oy; 4 YbBa2Ou3Oy. The highest YBa20U30y samples densities (6.09 g/cm 3) were obtained by hot pressing of the mixture containing 95 % of the superconducting phase at 800Oc and under the pressure of 750 MPa (Fig.2). The conditions for the preparation of the ceramics with the composition YBa2.xSrCu30y have been developed for x = 0.5; I; O; 1.5; 1.75. It has been found that during heat
1664
A.B. Blank et aL / Physico-chemical regularities
treatment in the argon flow there takes place I-2-3 phase decomposition followed by the oxygen loss (by a factor of 1.3) with Ba1_xSrxCuO 2 formation on the background of
phase which
one can observe the needles of STY204 and Y2Ba1_xSrxCuO 5 phases (electron probe microanalysis, X-ray analysis).
6.0 58 56
c ,IY°Y 70/0
0
5,2 $0
°c
An anomalous shape of the temperature curve of the electric resistance was observed for the compositions with x=1.5 (the drop of for more than an order at 180 K) and with x = = 1.75. However, this effect has poor reproducibility. Partial substitution of Y for Cr and Ti (Yo.8Cro.2Ba2Cu30y and Yo.8Tio.2Ba2Cu3Oy) deteriorates the superconducting properties and the stability of the ceramics. The application of the mentioned results allowed to develop the stable process for the preparation of the ceramics with the reproducible properties: samples density - 95 %; T c = = 93-100 K; ~ T = I-2 K; I c = IO3A/cm 2 at 77 K.
4% 44
42
FIGURE 2 Hot-pressed ceramics density dependence upon temperature and pressure. The subsequent thermal treatment in oxygen leads to the reduction of I-2-3 phase and to the increase of the oxygen content bound to copper. A small amount of other phases remains. T c for this composition is 78-80 K. It has been found that for
REFERENCES
/I/ V.P.SemSnozhenko et al, Physicochemical and analytical control for the preparation of the ceramics with the preset properties. Dokl. Akad. Nauk Uk. SSR (in Russian), 1987, N 11. /2/ T.Woda, S.Adachi, T.~ihara, R.Inaba, S~bstitution effect of Sr for
Y21~2_xSrxCu30y samples thermally
Ba of high-T c
treated in the ambient air (x
YBa2Cu307_y ceramics. Jap. J. Appl° Phys. 26 (1987) pp.L706L708.
1.5)
the increase of x results in T c and lattice parameters decrease,as in /2/.
superconducting