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The influence of dopant ions on structure and properties in Tl-1212 and Tl-2212
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Physica C 235-240 (1994)541-542 North-Holland
The influence of dopant ions on structure and properties in T1-1212 and TI-2212 S.- G. Erikssonl, C. Str0ml, N. Winzek2, A. Simon3 and M. Mehring2 1Dept. of Inorg. Chem., CTH/GU, S-412 96 Gt~teborg, SWEDEN, 2Physikalisches Institut, Universit~t Stuttgart, Pfaffenwaldring 57, 7000 Stuttgart 80, GERMANY, 3Max-PlanckInstitut fur FestkSrperforschung, Heisenbergstrasse 1, 7000 Stuttgart 80, GERMANY By changing the Y/Ca ratio in T1-1212 and TI-2212 structure as well as properties alter. At a certain dopant level a discontinous change in atomic structure, T o Raman phonon modes and in 2°5T1 NMR Knight shift occur. We have also shown that La 3+ or Sr 2+ substitution at the Ba site, oxygen depletion, or insertion of hydrogen in the TI-2212 material affect structure and carrier concentration and thus T c. INTRODUCTION The thallium cuprate system show an extremely complex chemistry and factors such as thallium and oxygen contents have a strong influence on the structure and properties (1-8). By use of a new preparative method it is possible to control and minimise thallium losses and to prepare differently doped materials with a well defined composition (34, 9). EXPERIMENTAL Samples were prepared from appropriate mixtures of T1203, Ba(OH)2.H20, Sr(NO3)2, La203, C a t , Y203 and Cu(NO3)2.nH20. The synthesis was run in two steps, in the first step the mixtures were heated at 100 ° C / hour in AI203 crucibles with A1203 covers and finally kept at 760 ° C for 3 hours. In the second sintering step the samples were sintered in in A1203 crucibles with covers and gold gaskets used as seals. Only minor losses of thallium, if any at all, takes place during the reaction (3- 4). Sample purity and lattice parameters were determined from Guinier film data using silicon (NBS 640b) as an internal standard. Neutron powder diffraction data were collected at the pulsed neutron source ISIS, RAL, UK using the high flux, medium reso-lution powder diffractometer POLARIS. A least-squares profile refinement program, TF14LS, based on the Rietveld technique was used for extraction of structural information. The NMR measurements were carried out using a home built pulsed NMR spectrometer operating around 105 MHz at a field of 4.26 T. Thallium occupies two different lattice sites denoted TI(1) and TI(2) corresponding to thallium in the "T1204" layers and at the Ca site, respectively. The sites are distinguishable by their resonance frequencies (10). The superconducting properties were studied by ac susceptibility measurements using a Quantum 0921-4534/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)00832-9
Design SQUID magnetometer at temperatures down to 4 K in a field of 50 Gauss. RESULTS AND DISCUSSION We have studied the influence various dopant ions have on carrier concentration, n, and To. In figure 1 a schematic illustration of the situation is presented.
T~
v
Carrier concentration,
n
Figure 1 The change in Te plotted as a function of carder concentration, n, induced by different dopant ions (n is derived from bond distance changes, 205T1 NMR and Cu NMR data). In the T l 2 B a 2 _ x M e x C a C u 2 0 8 _ d system no dramatic change in Tc is found at x< 0.6. The structural changes can roughly be rationalised in terms of a general compression of the structure. A drastic change in carder concentration and thus in structure and T c is in our samples expected to occur in the region 0.6< x< 1.0. In materials with a somewhat lower thallium content the drop occurs above x= 1.0 (11). With La 3+ substitution at the Ba site the situation is different. T c is strongly depressed and supercon-
542
S.-(;. EriL~.son e~ a l . / P h v s i c a (" 235 240 (1~)94) 54[ 542
ductivity vanishes at x= 0.3. The drop in Tc as a function of 205T1 NMR Knight shift is much faster in La3+ doped than in y3+ doped T1-2212 (See figure 2). From Rietveld refinement of neutron powder diffraction data one notice a continous increase in the isotropic temperature factor of the Ba/La atom. These findings indicate that the drop in Tc may be due to not only a change in carrier concentration in the C u t 2 planes, but also to a disturbance at the Ba site itself. 120
80 ~2 60 4O 2O 0
Figure 2 Tc as a function of 205T1 NMR Knight shift for a) T12Ba2.xLaxCaCu208.d and for b) Tl2Ba2Cal_xYxCu208.d . 29,4
A C
29,3.
B
29,2
29,1 0,00
ACKNOWI .EI'~EMENT Many thanks to S. Hull. ISIS, RAL, England for assitance in the collection of neutron diffraction data, and to R. K. Kremer, MPI, Stuttgart, Germany, and to H. Mazaki and H. Yasuoka for support with susceptibility measurements. We also wish to thank M. Kakihana, TIT, Tokyo, Japan, for Raman data. The financial support given by the Swedish Natural Science Research Council is gratefully acknowledged.
~
-3600 -3400 -3200 -3000 -2800 -2600 Ks
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higher dopant concentration, x, has been made in non thallium deficient TI- 1212. A more straightforward way to alter the carrier concentration and thus Tc in TI-2212 is by decreasing the oxygen content or by insertion of hydrogen into the structure. Oxygen is depleted out of the "T1204" layers, while the position of hydrogen in the structure is not yet known. In both cases the number of hole carriers decrease.
"
!
"
'
0,10
0,20
0,30
X
Figure 3 The c-axis length as a function of x in T12_yBa2Cal.xYxCu2Os. d in as prepared materials with a) 2-y= 2.0, b) 2-y= 1.9 and in oxygen annealed materials c) with 2-y= 2.0. In figure 3 the c- axis length is plotted as a function of x for two different values of y in the TI2_ yBa2Cal-xYxCu208_d system. An abrupt change coincides with a change in T c, carrier concentration and certain Raman mode frequencies at x=0.15; y=0.10. A redistribution of TI between the "T1204" layers and the Ca site seems to play an important role in this context. A similar finding, but at a
REFERENCES C. Michel, C. Martin, M. Hervieu, A. Maignan, J. Provost, M. Huve and B. Raveau, JSSC 96, 271 (1992) 2. Y. Shimakawa, Physica C204, 247 (1993) 3. C. Str0m, S.- G. Eriksson, L.- G. Johansson, A. Simon, Hj. Mattausch and R. K. Kremer, JSSC 109, 321 (1994) 4. C. Str0m, Thesis, University of Gtiteborg, December 1993 5. S.- G. Eriksson, C. Str6m and N. Winzek, Conference Proceeding, May 17-19, 1993, Erice, Italy 6. S.- G. Eriksson, C. StrOm, N. Winzek, R. K. Kremer, A. Simon and M. Mehring, ICMAS- 93, pp. 173-178, Dec. 10-13, 1993, Paris, France 7. C. Str0m, S.- G. Eriksson, N. Winzek, R. K. Kremer and A. Simon, ICMAS- 93, pp. 185-190, Dec. 10-13, 1993, Paris, France 8. M. Kakihana, C. Strtim, S.- G. Eriksson, H. MnTnki, H. Yasuoka and M. Yoshimura, ICMAS- 93, pp. 179-184, Dec. 10-13, 1993, Paris, France 9. L.- G. Johansson, C. Str/~m, S.- G. Eriksson and I. Bryntze, Physica C 220, 295 (1994) 10. N. Winzek, Hj. Mattausch, S.- G. Eriksson, C. Str/)m, R. K. Kremer, A. Simon and M. Mehring, Physica C 205, 45 (1993) 11. E.A. Hayri and M. Greenblatt, Physica C156, 11 (1988) 1.
Physica C 235-240 (1994)541-542 North-Holland
The influence of dopant ions on structure and properties in T1-1212 and TI-2212 S.- G. Erikssonl, C. Str0ml, N. Winzek2, A. Simon3 and M. Mehring2 1Dept. of Inorg. Chem., CTH/GU, S-412 96 Gt~teborg, SWEDEN, 2Physikalisches Institut, Universit~t Stuttgart, Pfaffenwaldring 57, 7000 Stuttgart 80, GERMANY, 3Max-PlanckInstitut fur FestkSrperforschung, Heisenbergstrasse 1, 7000 Stuttgart 80, GERMANY By changing the Y/Ca ratio in T1-1212 and TI-2212 structure as well as properties alter. At a certain dopant level a discontinous change in atomic structure, T o Raman phonon modes and in 2°5T1 NMR Knight shift occur. We have also shown that La 3+ or Sr 2+ substitution at the Ba site, oxygen depletion, or insertion of hydrogen in the TI-2212 material affect structure and carrier concentration and thus T c. INTRODUCTION The thallium cuprate system show an extremely complex chemistry and factors such as thallium and oxygen contents have a strong influence on the structure and properties (1-8). By use of a new preparative method it is possible to control and minimise thallium losses and to prepare differently doped materials with a well defined composition (34, 9). EXPERIMENTAL Samples were prepared from appropriate mixtures of T1203, Ba(OH)2.H20, Sr(NO3)2, La203, C a t , Y203 and Cu(NO3)2.nH20. The synthesis was run in two steps, in the first step the mixtures were heated at 100 ° C / hour in AI203 crucibles with A1203 covers and finally kept at 760 ° C for 3 hours. In the second sintering step the samples were sintered in in A1203 crucibles with covers and gold gaskets used as seals. Only minor losses of thallium, if any at all, takes place during the reaction (3- 4). Sample purity and lattice parameters were determined from Guinier film data using silicon (NBS 640b) as an internal standard. Neutron powder diffraction data were collected at the pulsed neutron source ISIS, RAL, UK using the high flux, medium reso-lution powder diffractometer POLARIS. A least-squares profile refinement program, TF14LS, based on the Rietveld technique was used for extraction of structural information. The NMR measurements were carried out using a home built pulsed NMR spectrometer operating around 105 MHz at a field of 4.26 T. Thallium occupies two different lattice sites denoted TI(1) and TI(2) corresponding to thallium in the "T1204" layers and at the Ca site, respectively. The sites are distinguishable by their resonance frequencies (10). The superconducting properties were studied by ac susceptibility measurements using a Quantum 0921-4534/94/$07.00 © 1994 - Elsevier Science B.V. All rights reserved. SSDI 0921-4534(94)00832-9
Design SQUID magnetometer at temperatures down to 4 K in a field of 50 Gauss. RESULTS AND DISCUSSION We have studied the influence various dopant ions have on carrier concentration, n, and To. In figure 1 a schematic illustration of the situation is presented.
T~
v
Carrier concentration,
n
Figure 1 The change in Te plotted as a function of carder concentration, n, induced by different dopant ions (n is derived from bond distance changes, 205T1 NMR and Cu NMR data). In the T l 2 B a 2 _ x M e x C a C u 2 0 8 _ d system no dramatic change in Tc is found at x< 0.6. The structural changes can roughly be rationalised in terms of a general compression of the structure. A drastic change in carder concentration and thus in structure and T c is in our samples expected to occur in the region 0.6< x< 1.0. In materials with a somewhat lower thallium content the drop occurs above x= 1.0 (11). With La 3+ substitution at the Ba site the situation is different. T c is strongly depressed and supercon-
542
S.-(;. EriL~.son e~ a l . / P h v s i c a (" 235 240 (1~)94) 54[ 542
ductivity vanishes at x= 0.3. The drop in Tc as a function of 205T1 NMR Knight shift is much faster in La3+ doped than in y3+ doped T1-2212 (See figure 2). From Rietveld refinement of neutron powder diffraction data one notice a continous increase in the isotropic temperature factor of the Ba/La atom. These findings indicate that the drop in Tc may be due to not only a change in carrier concentration in the C u t 2 planes, but also to a disturbance at the Ba site itself. 120
80 ~2 60 4O 2O 0
Figure 2 Tc as a function of 205T1 NMR Knight shift for a) T12Ba2.xLaxCaCu208.d and for b) Tl2Ba2Cal_xYxCu208.d . 29,4
A C
29,3.
B
29,2
29,1 0,00
ACKNOWI .EI'~EMENT Many thanks to S. Hull. ISIS, RAL, England for assitance in the collection of neutron diffraction data, and to R. K. Kremer, MPI, Stuttgart, Germany, and to H. Mazaki and H. Yasuoka for support with susceptibility measurements. We also wish to thank M. Kakihana, TIT, Tokyo, Japan, for Raman data. The financial support given by the Swedish Natural Science Research Council is gratefully acknowledged.
~
-3600 -3400 -3200 -3000 -2800 -2600 Ks
..<
higher dopant concentration, x, has been made in non thallium deficient TI- 1212. A more straightforward way to alter the carrier concentration and thus Tc in TI-2212 is by decreasing the oxygen content or by insertion of hydrogen into the structure. Oxygen is depleted out of the "T1204" layers, while the position of hydrogen in the structure is not yet known. In both cases the number of hole carriers decrease.
"
!
"
'
0,10
0,20
0,30
X
Figure 3 The c-axis length as a function of x in T12_yBa2Cal.xYxCu2Os. d in as prepared materials with a) 2-y= 2.0, b) 2-y= 1.9 and in oxygen annealed materials c) with 2-y= 2.0. In figure 3 the c- axis length is plotted as a function of x for two different values of y in the TI2_ yBa2Cal-xYxCu208_d system. An abrupt change coincides with a change in T c, carrier concentration and certain Raman mode frequencies at x=0.15; y=0.10. A redistribution of TI between the "T1204" layers and the Ca site seems to play an important role in this context. A similar finding, but at a
REFERENCES C. Michel, C. Martin, M. Hervieu, A. Maignan, J. Provost, M. Huve and B. Raveau, JSSC 96, 271 (1992) 2. Y. Shimakawa, Physica C204, 247 (1993) 3. C. Str0m, S.- G. Eriksson, L.- G. Johansson, A. Simon, Hj. Mattausch and R. K. Kremer, JSSC 109, 321 (1994) 4. C. Str0m, Thesis, University of Gtiteborg, December 1993 5. S.- G. Eriksson, C. Str6m and N. Winzek, Conference Proceeding, May 17-19, 1993, Erice, Italy 6. S.- G. Eriksson, C. StrOm, N. Winzek, R. K. Kremer, A. Simon and M. Mehring, ICMAS- 93, pp. 173-178, Dec. 10-13, 1993, Paris, France 7. C. Str0m, S.- G. Eriksson, N. Winzek, R. K. Kremer and A. Simon, ICMAS- 93, pp. 185-190, Dec. 10-13, 1993, Paris, France 8. M. Kakihana, C. Strtim, S.- G. Eriksson, H. MnTnki, H. Yasuoka and M. Yoshimura, ICMAS- 93, pp. 179-184, Dec. 10-13, 1993, Paris, France 9. L.- G. Johansson, C. Str/~m, S.- G. Eriksson and I. Bryntze, Physica C 220, 295 (1994) 10. N. Winzek, Hj. Mattausch, S.- G. Eriksson, C. Str/)m, R. K. Kremer, A. Simon and M. Mehring, Physica C 205, 45 (1993) 11. E.A. Hayri and M. Greenblatt, Physica C156, 11 (1988) 1.