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GdBa2CU3O7 under high pressure and at low temperatures
Physica C 153-155 (1988) 954-955 North-Holland, Amsterdam
GdBa2Cu307 UNDER HIGH PRESSURE AND AT LOW TEMPERATURES J.Ecke, W.H.Fietz, M.R.Dietrich, C.A.Wassilew, H.W0hl, R.FlCikiger Kernforschungszentrum Karlsruhe, Institut fCir Technische Physik, and Universit~t Karlsruhe, D-7500 Karlsruhe, P.O.Box 3640, Fed.Rep.of Germany We have investigated GdBa2Cu307 under high pressure and at low temperatures by means of X-ray diffraction. The bulkmodulus is 1550 kbar at 300 K . Thus GdBa2Cu307 is more compressible than YBazCu307 with a bulkmodulus of 1700 kbar. The structure of GdBa2Cu307 remains orthorhombic in the investigated pressure range with a preferential c-axis decrease under pressure. Since the discovery of superconductivity in the perowskite-type ceramic oxides (1) a whole class of materials with Tc of about 92 K was found (2,3,4). The strong Tc-increase under pressure is a characteristic feature of these materials. In this work we present the results of our structural investigations of GdBa2Cu307 under high pressure at various temperatures. I. Experimental The GdBa2Cu307 sample was prepared by reacting mixtures of Gd203 , BaCO3 and CuO for 14h at 930 °C in air which wasrepeated twice after intermediate grinding and cold pressing. The sample was submitted to a heat treatment of 4 h at 950 °C in flowing oxygen gas, followed by cooling at a rate of 100 °C / hour. The inductivly measured transition temperature is 92.5 K and has a width of 3 K . The resistivity ratio is 2,44 with a resistivity of 330 p~em at 100 K. The powdered sample is mixed with NaF
Temperature 300K 150K 15 K
which serves as a soft pressure transmitting medium. Lessthen 10 lag of this mixture is filled in a 0.2 mm bore of an inconell gasket and enclosed by the diamonds of a high-pressure cell (5). The cell is placed in a gasflow cryostat, which permits temperatures from 5 to 300 K. The pressure is measured by the ruby-method (6). For the structural investigation we use Mo-ko radiation with a self-focussing arrangement and a position sensitiv detector (7). II. Results The lattice parameters of GdBa2Cu307 which were calculated from the obtained spectra at ambient pressure and several temperatures are shown in Tab.1. Many reflections overlap in the o b t a i n e d spectra because the length of the c-axis is about 3-times the length of the b-axis. For example the (006) and the (020) reflections superpose and are t h e r e f o r e n o t r e s o l v a b l e . Due t o t h e orthorhombic splitting of the a- and b-axis the
a-axis 3.839 ~, 3.832 A
b-axis 3.893 ~, 3.892 A
c-axis 11.686 ~, 11.647 ~,
3.829 A
3.889 ~,
11.646 ~,
Tab. 1: Lattice-parameters of GdBa2Cu307 at several temperatures 0921-4534/88/$03.50 ©Elsevier Science Publishers B.V.
(North:Holland PhysicsPublishingDivision)
J. Ecke et aL / GdBa2Cu307 under high pressure and at low temperatures
(200) reflection is close to this double-peak. Under pressure the (020) and (006) peaks split and form a broad peak interfering with the (200) reflection. This indicates an unequal decrease of the b and c lattice parameters with applied pressure. We assume a stronger decrease of the c-axis with increasing pressure. Thus GdBa2Cu307 remains orthorhombic in the investigated pressure range up to 150 kbar. The assumption of a stronger decreasing c-axis is supported by Xray measurements, which show the c-axis to be very sensitive upon oxygen depletion (8). In addition structural investigations at various t e m p e r a t u r e s show no change of t h e a/b-ratio (9). The decrease of the lattice parameters under pressure is 2.3%, 2.1% and 3.9% for the a-, band c-axis at 140 kbar, respectively. GdBa~Cu307
1.00 x
V/Vo
A
x
x xzx
0.96
n n
,a
~
-F=300
K
F=150
K
T-<
K
IN
×
= Ax u
xa
0.92 ~× A u
0.88
~
0
50
,
L
100
150 Pressure [kbar]
Fig.l: Normalized volume decrease of GdBa2Cu307 as a function of pressure Fig.1 shows the normalized volume as a function of pressure. The resulting bulkmodulus is 1550,1600,1650 (+/-150) kbar at 300, 150, 15 K, respectively. Discussion These results show GdBa2Cu307 to be softer than YBa2Cu30 7 with a b u l k m o d u l u s of 1800 kbar (10). The lower bulkmodulus may arise from the enhancement of the unit-cell volume due to the larger Gd ion. This enlarged unit cell III.
is more sensitive to applied pressure, which corresponds to a stronger decrease of the lattice parameters under pressure. The h i g h e r compressibility of GdBa2Cu30 7 leads to the e x p e c t a t i o n of a h i g h e r T c increase o f GdBa2Cu307 under pressure in comparison with YBa2Cu307 , which is in agreement with (11,12). We thank B. Runtsch for her valuable help.
(1)
J.G.Bednorz, K.A. M011er: Z. Phys. B Condensed Matter 64, 189 (1986) (2) M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang, C.W. Chu: Phys. Rev. Lett. 58, 908 (1987) (3) S. Tsurumi, M. Hikita, T. Iwata, K. Semba, S. Kurihara: Jap. J. Appl. Phys. 26, L856 (1987) (4) K.N. Yang, Y. Dalichaouch, J.M. Ferreira, B.W. Lee, J.J. Neumeier, M.S. Torikachvili, H. Zhou, M.B. Maple: Sol. Stat. Com. 63, 515 (1987) (5) R. Keller, W.B. Holzapfei: Rev. Sci. Instrum. 48, 517 (1977) (6) D.J.Piermarini, S. Block, J.D. Barnett, R.A. Foreman: J. Appl, Phys. 46, 6 (1975) (7) W.H. Fietz, M,R. Dietrich, H. W0hl: (to be published) (8) J.M. Tarascon, W.R. McKinnon, L.H. Greene, G.W. Hull, E.M. Vogel: Phys. Rev. B 36, 226 (1987) (9) N. Yamamoto, Y. Hirotsu, Y. Murata, S.Nagakura, M. Takata: J. Electron Microsc. 36 (4), 256 (1987) (10) W.H. Fietz, M.R. Dietrich, J. Ecke: Z. Phys. B Condensed Matter 69, 17 (1987) (11) H.A. Borges, R. Kwok, JD. Thompson, G.L. Wells, Ji. Smith, Z. Fisk, D.E. Peterson: Phys. Rev. B 36,2404 (1987) (12) S. Yomo, C. Murayama, W. Utsumi, H. Takahashi, T. Yagi, N. Mori, T. Tamegai, A. Watanbe, Y. lye: Jap. J. Appl. Phys 26, 1107 (1987)
955
GdBa2Cu307 UNDER HIGH PRESSURE AND AT LOW TEMPERATURES J.Ecke, W.H.Fietz, M.R.Dietrich, C.A.Wassilew, H.W0hl, R.FlCikiger Kernforschungszentrum Karlsruhe, Institut fCir Technische Physik, and Universit~t Karlsruhe, D-7500 Karlsruhe, P.O.Box 3640, Fed.Rep.of Germany We have investigated GdBa2Cu307 under high pressure and at low temperatures by means of X-ray diffraction. The bulkmodulus is 1550 kbar at 300 K . Thus GdBa2Cu307 is more compressible than YBazCu307 with a bulkmodulus of 1700 kbar. The structure of GdBa2Cu307 remains orthorhombic in the investigated pressure range with a preferential c-axis decrease under pressure. Since the discovery of superconductivity in the perowskite-type ceramic oxides (1) a whole class of materials with Tc of about 92 K was found (2,3,4). The strong Tc-increase under pressure is a characteristic feature of these materials. In this work we present the results of our structural investigations of GdBa2Cu307 under high pressure at various temperatures. I. Experimental The GdBa2Cu307 sample was prepared by reacting mixtures of Gd203 , BaCO3 and CuO for 14h at 930 °C in air which wasrepeated twice after intermediate grinding and cold pressing. The sample was submitted to a heat treatment of 4 h at 950 °C in flowing oxygen gas, followed by cooling at a rate of 100 °C / hour. The inductivly measured transition temperature is 92.5 K and has a width of 3 K . The resistivity ratio is 2,44 with a resistivity of 330 p~em at 100 K. The powdered sample is mixed with NaF
Temperature 300K 150K 15 K
which serves as a soft pressure transmitting medium. Lessthen 10 lag of this mixture is filled in a 0.2 mm bore of an inconell gasket and enclosed by the diamonds of a high-pressure cell (5). The cell is placed in a gasflow cryostat, which permits temperatures from 5 to 300 K. The pressure is measured by the ruby-method (6). For the structural investigation we use Mo-ko radiation with a self-focussing arrangement and a position sensitiv detector (7). II. Results The lattice parameters of GdBa2Cu307 which were calculated from the obtained spectra at ambient pressure and several temperatures are shown in Tab.1. Many reflections overlap in the o b t a i n e d spectra because the length of the c-axis is about 3-times the length of the b-axis. For example the (006) and the (020) reflections superpose and are t h e r e f o r e n o t r e s o l v a b l e . Due t o t h e orthorhombic splitting of the a- and b-axis the
a-axis 3.839 ~, 3.832 A
b-axis 3.893 ~, 3.892 A
c-axis 11.686 ~, 11.647 ~,
3.829 A
3.889 ~,
11.646 ~,
Tab. 1: Lattice-parameters of GdBa2Cu307 at several temperatures 0921-4534/88/$03.50 ©Elsevier Science Publishers B.V.
(North:Holland PhysicsPublishingDivision)
J. Ecke et aL / GdBa2Cu307 under high pressure and at low temperatures
(200) reflection is close to this double-peak. Under pressure the (020) and (006) peaks split and form a broad peak interfering with the (200) reflection. This indicates an unequal decrease of the b and c lattice parameters with applied pressure. We assume a stronger decrease of the c-axis with increasing pressure. Thus GdBa2Cu307 remains orthorhombic in the investigated pressure range up to 150 kbar. The assumption of a stronger decreasing c-axis is supported by Xray measurements, which show the c-axis to be very sensitive upon oxygen depletion (8). In addition structural investigations at various t e m p e r a t u r e s show no change of t h e a/b-ratio (9). The decrease of the lattice parameters under pressure is 2.3%, 2.1% and 3.9% for the a-, band c-axis at 140 kbar, respectively. GdBa~Cu307
1.00 x
V/Vo
A
x
x xzx
0.96
n n
,a
~
-F=300
K
F=150
K
T-<
K
IN
×
= Ax u
xa
0.92 ~× A u
0.88
~
0
50
,
L
100
150 Pressure [kbar]
Fig.l: Normalized volume decrease of GdBa2Cu307 as a function of pressure Fig.1 shows the normalized volume as a function of pressure. The resulting bulkmodulus is 1550,1600,1650 (+/-150) kbar at 300, 150, 15 K, respectively. Discussion These results show GdBa2Cu307 to be softer than YBa2Cu30 7 with a b u l k m o d u l u s of 1800 kbar (10). The lower bulkmodulus may arise from the enhancement of the unit-cell volume due to the larger Gd ion. This enlarged unit cell III.
is more sensitive to applied pressure, which corresponds to a stronger decrease of the lattice parameters under pressure. The h i g h e r compressibility of GdBa2Cu30 7 leads to the e x p e c t a t i o n of a h i g h e r T c increase o f GdBa2Cu307 under pressure in comparison with YBa2Cu307 , which is in agreement with (11,12). We thank B. Runtsch for her valuable help.
(1)
J.G.Bednorz, K.A. M011er: Z. Phys. B Condensed Matter 64, 189 (1986) (2) M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao, Z.J. Huang, Y.Q. Wang, C.W. Chu: Phys. Rev. Lett. 58, 908 (1987) (3) S. Tsurumi, M. Hikita, T. Iwata, K. Semba, S. Kurihara: Jap. J. Appl. Phys. 26, L856 (1987) (4) K.N. Yang, Y. Dalichaouch, J.M. Ferreira, B.W. Lee, J.J. Neumeier, M.S. Torikachvili, H. Zhou, M.B. Maple: Sol. Stat. Com. 63, 515 (1987) (5) R. Keller, W.B. Holzapfei: Rev. Sci. Instrum. 48, 517 (1977) (6) D.J.Piermarini, S. Block, J.D. Barnett, R.A. Foreman: J. Appl, Phys. 46, 6 (1975) (7) W.H. Fietz, M,R. Dietrich, H. W0hl: (to be published) (8) J.M. Tarascon, W.R. McKinnon, L.H. Greene, G.W. Hull, E.M. Vogel: Phys. Rev. B 36, 226 (1987) (9) N. Yamamoto, Y. Hirotsu, Y. Murata, S.Nagakura, M. Takata: J. Electron Microsc. 36 (4), 256 (1987) (10) W.H. Fietz, M.R. Dietrich, J. Ecke: Z. Phys. B Condensed Matter 69, 17 (1987) (11) H.A. Borges, R. Kwok, JD. Thompson, G.L. Wells, Ji. Smith, Z. Fisk, D.E. Peterson: Phys. Rev. B 36,2404 (1987) (12) S. Yomo, C. Murayama, W. Utsumi, H. Takahashi, T. Yagi, N. Mori, T. Tamegai, A. Watanbe, Y. lye: Jap. J. Appl. Phys 26, 1107 (1987)
955