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Thin domain walls in YBa2Cu3O7−x: An X-ray diffraction study
Physica C 235-240 (I 994) 1265-1266 North-Holland
PHYSICA
Thin domain walls in YBazCuaO7_x: An X-ray diffraction study Jutta Chrosch and Ekhard K H Salje Interdisciplinary Research Centre in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK Twin walls of orthorhombic single crystals of YBazCU3OT.x (YBCO) were investigated using a high resolution X-ray diffractometer. Diffraction and rocking curves were recorded for split (0kl)/(h01) pairs of Bragg peaks. Numerical fits yielded an average wall thickness of 7(2) A with an approximate distance of 250 A. 1. INTRODUCTION Twinning in YBCO is produced by a ferroelastic phase transition at about 1020K [ 1,2] or at lower temperatures in Co or Fe doped samples [3,4] during which twins spontaneously appear to compensate the internal strains. The resulting two different types of boundaries are oriented parallel to [1101 and [110], respectively. Their structural nature has been investigated previously using electron microscopic techniques (for references see [5]). The main motivation for our reinvestigation lies in the potential effect of twinning on the superconducting transition. In order to explore the microstructural features from a different perspective we used high resolution X-ray diffractometry to determine the twin density and twin wall thickness.
The diffraction experiments were carried out using the experimental arrangement described in detail in [5] and [6]. 3. THEORY In order to analyse the wall related diffraction pattern we considered a theoretical wall profile leading to a displacement pattern which could be titled with a linear model. In Fig. 1 we plotted the dependence of the wall related intensity on the wall thickness as the result of this calculation. Notice the linear dependence on larger values of w. The ratio of wall related and total intensity can then be determined and the wall thickness w and distance d be extracted from the experimental observations [5].
2. EXPERIMENT
QIQ00 Large single crystals of YBCO were chosen from different growth experiments. Their oxygen content was characterized by susceptibility measurements. All investigated samples possess a sharp transition at Tc=90 K. Further criteria were visible domains in the polarizing microscope and nearly no bending of the surface. The samples were mounted with plasticine or a drop of glycerine on a glass plate for the measurements.
,QO "--~. 4 ~3i dOOQe'w ~ 12~eeee
wall thickness (A) Fig. 1: Dependence of the wall related intensity on the wall thickness.
0921-4534/94/S07.00© 1994- ElsevierScience B.V. All rights reserved. SSDI 0921-4534(94)01196-6
J. Chrosch, E.K.H. Salje/Physica C 235-240 (1994) 1265-1266
1266
4. RESULTS
This value is identical to the Ginzburg conjecture gTc/A=a 2 and we are now able to
Fig. 2 shows a rocking curve of the split peaks (029)/(209) with excess intensity in between and their respective numerical fit. The intensity can be related to a superposition of diffraction signals from twin walls and from the orthorhombic bulk material.
estimate the Ginzburg parameter as g,=10-2° Jm 2 / mol K (see [5] for more details).
°:o[
11.2
11.3
11.4
11.5 11.6
11.7
11.8
tilt (deg)
Fig. 2: Rocking curve of (029) and (209) and its numerical fit. The relative integrated intensity difference is of
the order of 3% yielding a wail thickness of--. 7A. Supposing that the whole crystal is twinned we get an average distance between the domains of the order of 250A wllich is consistent with HRTEM measurements on the same sample [7].
5. DISCUSSION Our main experimental finding is that twin walls in YBCO are only about one or two unit cells thick at room temperature. Comparing the thickness of the domain walls with the prediction of the Landau-Ginzburg th~ry of the ferroelastic phase transition in YBCO we find with Tc~1020K and T=300K gTc/A--a 2 where a is the lattice constant perpendicular to the wall (~-5.5A).
REFERENCES [11 Roth, G., Ewert, D., Hervieu, M., Michel, C.. Raveau, B., D'Yvoire, F., Revcolevschi, A., Z. Phys. B69 (1987) 21. [2] Van Tendeloo, G., Zandbergen, H.W., Amelinckx, S., Solid State Commun. 63 (1987) 389. [31 Schmahl, W.W., Putnis, A., Salje, E. K. H., Freeman, P., Graeme-Barber, A., Jones, R., Singh, K.K., Blunt, J., Edwards, P.P., Loram, J., Mirza, K., Phil. Mag. Letters 60 (1989) 241. [4] Krekels, T., Van Tendeloo, G., Broddin, D., Amelinckx, S., Tanner, L., Mehbod, M., Vanlanthem, E., Dcltour, R., Physica C 173 (i991) 361. [5] Chrosch, J., Salje, E.K.H., Physica C (1994) in press. [6] Wruck, B., Salje, E.K.H., Zhang, M., Abraham, T., Bismayer, U., Phase Trans. 48 (1994) 135. [7] Yang, Y., personal communication.
PHYSICA
Thin domain walls in YBazCuaO7_x: An X-ray diffraction study Jutta Chrosch and Ekhard K H Salje Interdisciplinary Research Centre in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK Twin walls of orthorhombic single crystals of YBazCU3OT.x (YBCO) were investigated using a high resolution X-ray diffractometer. Diffraction and rocking curves were recorded for split (0kl)/(h01) pairs of Bragg peaks. Numerical fits yielded an average wall thickness of 7(2) A with an approximate distance of 250 A. 1. INTRODUCTION Twinning in YBCO is produced by a ferroelastic phase transition at about 1020K [ 1,2] or at lower temperatures in Co or Fe doped samples [3,4] during which twins spontaneously appear to compensate the internal strains. The resulting two different types of boundaries are oriented parallel to [1101 and [110], respectively. Their structural nature has been investigated previously using electron microscopic techniques (for references see [5]). The main motivation for our reinvestigation lies in the potential effect of twinning on the superconducting transition. In order to explore the microstructural features from a different perspective we used high resolution X-ray diffractometry to determine the twin density and twin wall thickness.
The diffraction experiments were carried out using the experimental arrangement described in detail in [5] and [6]. 3. THEORY In order to analyse the wall related diffraction pattern we considered a theoretical wall profile leading to a displacement pattern which could be titled with a linear model. In Fig. 1 we plotted the dependence of the wall related intensity on the wall thickness as the result of this calculation. Notice the linear dependence on larger values of w. The ratio of wall related and total intensity can then be determined and the wall thickness w and distance d be extracted from the experimental observations [5].
2. EXPERIMENT
QIQ00 Large single crystals of YBCO were chosen from different growth experiments. Their oxygen content was characterized by susceptibility measurements. All investigated samples possess a sharp transition at Tc=90 K. Further criteria were visible domains in the polarizing microscope and nearly no bending of the surface. The samples were mounted with plasticine or a drop of glycerine on a glass plate for the measurements.
,QO "--~. 4 ~3i dOOQe'w ~ 12~eeee
wall thickness (A) Fig. 1: Dependence of the wall related intensity on the wall thickness.
0921-4534/94/S07.00© 1994- ElsevierScience B.V. All rights reserved. SSDI 0921-4534(94)01196-6
J. Chrosch, E.K.H. Salje/Physica C 235-240 (1994) 1265-1266
1266
4. RESULTS
This value is identical to the Ginzburg conjecture gTc/A=a 2 and we are now able to
Fig. 2 shows a rocking curve of the split peaks (029)/(209) with excess intensity in between and their respective numerical fit. The intensity can be related to a superposition of diffraction signals from twin walls and from the orthorhombic bulk material.
estimate the Ginzburg parameter as g,=10-2° Jm 2 / mol K (see [5] for more details).
°:o[
11.2
11.3
11.4
11.5 11.6
11.7
11.8
tilt (deg)
Fig. 2: Rocking curve of (029) and (209) and its numerical fit. The relative integrated intensity difference is of
the order of 3% yielding a wail thickness of--. 7A. Supposing that the whole crystal is twinned we get an average distance between the domains of the order of 250A wllich is consistent with HRTEM measurements on the same sample [7].
5. DISCUSSION Our main experimental finding is that twin walls in YBCO are only about one or two unit cells thick at room temperature. Comparing the thickness of the domain walls with the prediction of the Landau-Ginzburg th~ry of the ferroelastic phase transition in YBCO we find with Tc~1020K and T=300K gTc/A--a 2 where a is the lattice constant perpendicular to the wall (~-5.5A).
REFERENCES [11 Roth, G., Ewert, D., Hervieu, M., Michel, C.. Raveau, B., D'Yvoire, F., Revcolevschi, A., Z. Phys. B69 (1987) 21. [2] Van Tendeloo, G., Zandbergen, H.W., Amelinckx, S., Solid State Commun. 63 (1987) 389. [31 Schmahl, W.W., Putnis, A., Salje, E. K. H., Freeman, P., Graeme-Barber, A., Jones, R., Singh, K.K., Blunt, J., Edwards, P.P., Loram, J., Mirza, K., Phil. Mag. Letters 60 (1989) 241. [4] Krekels, T., Van Tendeloo, G., Broddin, D., Amelinckx, S., Tanner, L., Mehbod, M., Vanlanthem, E., Dcltour, R., Physica C 173 (i991) 361. [5] Chrosch, J., Salje, E.K.H., Physica C (1994) in press. [6] Wruck, B., Salje, E.K.H., Zhang, M., Abraham, T., Bismayer, U., Phase Trans. 48 (1994) 135. [7] Yang, Y., personal communication.