Die ordnende Wirkung eines Saat-Kristalles auf die Textur einer massiven YBaCuO-Probe
					Um die Abhängigkeit der lokalen Textur von Teilen einer zylindrischen YBaCuO-Probe vom Abstand zum Saatkristall zu untersuchen, wurde eine sehr gut texturierte YBaCuO-Probe in 9 rechteckige und in 12 Randstücke zerschnitten. Von den einzelnen Teilen der YBaCuO-Probe wurden die Texturen mit Hilfe der Neutronen-Beugung am Reaktor in Geesthacht gemessen und zwar mit einem "equal-area"-Raster. Die Maschenweite betrug 1° bis zu einer Achsabweichung der Zylinderachse der originären YBaCuO-Probe von 10° und von 10° Achsabweichung bis zu 20° Achsabweichung betrug die Maschenweite 2°. Aus der Summe der gezählten Neutronen auf Kleinkreisen der Polkugel wurden die einzelnen Werte der Verteilung der Achsabweichungen der c-Achsen der kristallinen Domänen von der Zylinderachse berechnet. Die mittlere Achsabweichung der c-Achsen der kristallinen Domänen von der Zylinderachse der unzerschnittenen YBaCuO-Probe wächst vom inneren Stück mit dem Saatkristall zu den Randstücken der zylindrischen Probe hin an

Adam, M.

Bornemann, H.J.

Brokmeier, H.G.

Jung, V.

Kaiser, A.

Schnieber, R.

Bornemann, H. J.

Brokmeier, H. G.

KITopen

Forschungszentrum Karlsruhe Technik und Umwelt FZKA 6072 The lnfluence of a Seed Crystal on the Texture of a Bulk YBaCuO Specimen V. Jung, M. Adam, H. J. Bornemann, H.-G. Brokmeier, A. Kaiser, R. Schnieber Institut für Nukleare Festkörperphysik Februar 1998 Forschungszentrum Karlsruhe Technik und Umwelt Wissenschaftliche Berichte FZKA6072 The Influence of a Seed Crystal on the Texture of a Bulk YBaCuO Specimen V. Jung, M. Adam, H.J. Bornemann, H. -G. Brokmeier*, A. Kaiser, R. Schnieber* Institut für Nukleare Festkörperphysik *IMM-TU Clausthal/GKSS Geesthacht, P.O.Box 1160, D-21494 Geesthacht Forschungszentrum Karlsruhe GmbH, Karlsruhe 1998 Als Manuskript gedruckt Für diesen Bericht behalten wir uns alle Rechte vor Forschungszentrum Karlsruhe GmbH Postfach 3640, 76021 Karlsruhe Mitglied der Hermann von Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF) ISSN 0947-8620 The Influence of a Seed Crystal on the Texture of a Bulk YBaCuO Specimen To investigate the dependence of the local texture of parts of an YBaCuO specimen on the di-stance of the seed crystal from the position of the part of the specimen, a very good textured YBaCuO specimen was cut into 9 reetangular pieces and into 12 boundary pieces of the cylin-dric original specimen. From the individual parts of the YBaCuO specimen the texture was measured by neutron diffraction at the Geesthacht reactor with an equal area raster. The grid width was 1 o up to 10° deviation from the cylinder axis of the original YBaCuO cylinder and 2° from 10° deviation until 20° deviation. From the sum of the counted neutrons on small cir-cles on the pole sphere the individual values of the distributions of the angular deviations of the c-axes of the crystalline domains from the cylinder axis have been calculated. The mean deviation of the c-axes from the axis of the original cylinder increases from the inner part with the seed crystal to the boundary parts of the cylindric YBaCuO specimen. Die ordnende Wirkung eines Saat-Kristalles auf die Textur einer massiven YBaCuO-Probe Um die Abhängigkeit der lokalen Textur von Teilen einer zylindrischen YBaCuO-Probe vom Abstand zum Saatkristall zu untersuchen, wurde eine sehr gut texturierte YBaCuO-Probe in 9 rechteckige und in 12 Randstücke zerschnitten. Von den einzelnen Teilen der YBaCuO-Probe wurden die Texturen mit Hilfe der Neutronen-Beugung am Reaktor in Geesthacht gemessen und zwar mit einem "equal-area"-Raster. Die Maschenweite betrug 1 o bis zu einer Achsab-weichung der Zylinderachse der originären YBaCuO-Probe von 10° und von 10° Achsab-weichung bis zu 20° Achsabweichung betrug die Maschenweite 2°. Aus der Summe der ge-zählten Neutronen auf Kleinkreisen der Polkugel wurden die einzelnen Werte der Verteilung der Achsabweichungen der c-Achsen der kristallinen Domänen von der Zylinderachse berech-net. Die mittlere Achsabweichung der c-Achsen der kristallinen Domänen von der Zylinder-achse der unzerschnittenen YBaCuO-Probe wächst vom inneren Stück mit dem Saatkristall zu den Randstücken der zylindrischen Probe hin an. As can be seen in Fig. 1, a cylindrical YBaCuO specimen of 43 mm diameter and 15 mm height was cut into nine reetangular pieces and twelve edge pieces for examination of the lo-cal texture of these parts. One aspect under study was the range of the erdering effect of the central seed crystal. Measurements of the texture of the pieces of the specimen indicated that the sum total of the full width at half maximum of the distribution of axial deviations of the c-axes of the crystal domains from the cylinder axis of the YBaCuO specimen and the axial deviation of the center of mass of the distribution increase continuously towards the edge of the specirrien. This sum total was produced because there may be narrow distributions with large distances of the cen-ter of mass as well as broader distributions with short distances of the center of mass from the cylinder axis. In most cases, however, both values - the width of distribution and the distance of the center of mass - increased towards the edge of the specimen in roughly the same way. The erdering effect of the seed crystal thus decreases towards the edge of the specimen. The other factor tobe studied was whether, with the sameglobal texture of the bulk speci-men, a speciallocal texture is able to change the potential maximum current carrying capacity of the superconductor [1]. A decisive factor in this respect is the way in which the distribution of orientations of the c-axes of the crystalline domains is tilted completely relative to the cyl-inder axis of the specimen. The axis of distribution may be tilted solely in the direction of the cylinder axis in such a way that the cylinder axis and the axis of distribution are situated in the same plane. In this case, the effect reducing the current carrying capacity is extremely slight, as the distribution axis is always normal to the direction of the superconducting currents flowing in concentric circles about the cylinder axis, if these currents are induced by an ap-proaching permanent magnet. 2 lf the a.xis of distribution of the c-a.xes of the domains is no Ionger normal to the direction of the superconducting currents, the influence of the tilt of the distribution a.xis of the c-a.xis distribution from the normal to the direction of the superconducting currents is more pro-nounced than in the case in which the a.xis of distribution is in the same plane as the cylinder a.xis [2]. This secend case wastobe studied by cutting the specimen and subsequently meas-uring the texture of the pieces. However, it is apparent from the texture measurements con-ducted that the latter effect does not occur in the specimen under study. Hence, interest was focused mainly upon the range of the erdering effect of the seed crystal implanted into the recrystallizing YBaCuO melt [3]. · After the pole spheres had been scanned with a raster of 1.5° in x and 2° in <p on great cir-cles in the range of 70° < x < 90° of the pieces of specimen M39 under study, this raster was found to be too coarse. With a rasterthat coarse, one measurement of the central region of the pole spheres of 70° < x < 90° took approximately 70 minutes. For subsequent measurements with a finer raster it was sufficient to apply that fine raster in the rang es of 80° < x < 90° and 90° < x < 100°. While a 1 o raster was used to measure in the central region, a 2° raster was sufficient for the 70° < x < 80° and 100° < x < 110° regions. This kept the the nurober of measuring points to be addressed within reasonable limits. Now it was possible, by measuring the distributions at X < 90° and at X > 90°, to eliminate by aver-aging any bias arising from the intensity of the neutron beam not being constant over the ver-tical beam divergence. This condition simulates a misalignment of the incident beam of 0.25° and, at 2 8 = 34°, causes apparent misalignment of the scattering vector of 0.45°. The inequality of the intensity distribution of the neutron beam over the vertical divergence is due to flaws in the Cu (111) single-crystal monochromator. At an expense of approx. DM 10,000 for a new Cu (111) single-crystal monochromator it is possible, however, to eliminate this apparent misalignment of the scattering vector. lf, after installation of a new monochromator, measurements at x < 90° and at X > 90° result in identical mirrar image dis-tributions, the necessary measuring time can be reduced by half if measurements are per-formed only at x < 90° or at x > 90°. Moreover, a new monochromator allows the neutron beam to be focused horizontally upon the Center of the specimen by an arrangement of Cu ( 111) single crystals on a circular arc of approx. 6 m radius [ 4]. 3 As no new Cu (111) single-crystal monochromatorwas available at short notice, the appar-ent misalignment of the scattering vector of 0,45° had to be put up with initially. Measuring the texture of a piece of the specimen with the measuring raster shown in Fig. 2 took ap-proximately three hours. As a consequence, it was not possible to measure all pieces of the M39 specimen. The pieces measured were the center piece, No.5, with the seed crystal; piece 2i between the center piece, No. 5, and the edge piece, No. 2 (see Fig. 1); the edge piece, No. 2; the adjacent piece, No. 3; and the edge pieces, No. 3a and 1a. The values of the neutrons counted as obtained from the measurement raster (see Fig. 2) were used to plot sections through the pole spheres. In the absence of any apparent misalign-ment of the scattering vector, these sections must be mirror images if the value of <p + 1t is set instead of the value of <p. The mean value obtained from the asymmetry of the centers of the intensity distributions was the value of apparent misalignment of the scattering vector of 0.45°. For the rest, the sections through the orientation distributions showed the narrowness of the full widths at half maximum of the sections through the distributions. Summing up the measured counting rates at identical axis deviations from the cylinder axis of the uncut specimen results in the values of the distributions of the deviations of the c-axes of the crystalline domains from the cylinder axis of the YBaCuO specimen [3]. These distri-butions of the sums of counting rates on small circles about the pole axis clearly indicate a right-left asymmetry caused by the apparent misalignment of the scattering vector. In order to obtain a measure of the quality of the texture, the sum total was produced of the full width at half maximum (FWHM) of the new distribution and the distance of the center of full width at half maximum from the x = 90°direction (LlX). Despite all differences in distri-butions, this sum total, (LlX + FWHM), is a tangible dimension increasing continuously from the center piece, No. 5, with the seed crystal to the edge piece, No. 3a and, in this way, clearly indicating the decreasing ordering effect of the seed crystal from the center to the edge of the specimen. The mean value of LlX + FWHM was produced in two ways: In one way, the value shown above was obtained from the distributions of X < 90° and for x > 90°, and the mean was pro-duced from the two values. In the other case, means were produced for each of the measured values, I x -n/21 , which represent the values of the averaged distribution. From this distribu-tion of mean values of the sums total of the measured values, a different value was obtained 4 for b..X + FWHM. These mean values obtained in two ways do not differ from each other in the center piece, No. 5, and differ by only 0.05° in the edge piece, No. 2. In the adjacent piece, No. 3 (see Fig. 1), the deviation is 0.15° throughout. Fig. 3a shows the sections through the pole sphere of the center piece, No. 5, while Fig. 3b shows the summation of the measured values on small circles about the direction of X = 90°. This applies correspondingly to piece No. 2i (Fig. 4a and Fig. 4b), the edge piece, No. 2 (Fig. 5a and Fig. Sb), the edge piece, No. 1a (Fig. 6a and Fig. 6b), the edge piece, No. 3a (Fig. 7a and Fig. 7b), and piece No. 3 (Fig. 8a and Fig. 8b). Figure 9, finally, provides an overview of all results, i.e. averaging of the right and left distributions from Fig. 3b to Fig. 8b. Further measurements to be performed with a new Cu (111) single-crystal monochromator are to provide information about the range of the erdering effect of the seed crystal in the depth of the superconducting YBaCuO material along the cylinder axis of the cylindrical specimens. References [1] Jung, V. et al.: Local Texture and Magnetic Levitation Force of YBaCuO Cylinders. Int. Conf. on Texture and Anisotropy of Polycrystals, Sept. 22-25, 1997, Clausthal, Ger-many, Material Science Forum, Feb./March (1998). [2] Bornemann, H.J. et al.: Semi-Finished Parts and Products Made from Melt-Textured Bulk YBCO Materials for Superconducting Magnetic Bearings, IEEE Transactions on Applied Superconductivity 7, pp. 1805-1808 (1997). [3] Jung, V. et al.: Texture of Superconducting YBaCuO-Cylinders ... , FZKA 5961, For-schungszentrum Karlsruhe, Juni 1997. [4] Brokmeier, H.-G.: Texturanalyse mittels winkeldispersiver neutronengraphischer Kern-streuung, GKSS 95/E/9 (1995) Geesthacht, Germany. 2 11.5' 10.65' 1 7.9' 7.95' 4 5 6 7 9 Fig. 1: YBaCuO cylinder with cut lines and numbers of the pieces. The values of degrees represent the sum of l.lX + FWHM of the distributions in Fig. 9. Neutrons Neutrons 6000 6000 Center at 4000 tJ. x = 1.so 4000 X= 90.20° FWHM = 5.6° FWHM = 6.6° @J M 39 @J M 39 5 6. 5 2000 'P = oo 2000 'P = 120° 5 Fig. 2: Equal area raster for measuring of orientation distributions of the c-axes of the crystalline domains of the different pieces of specimen M 39. Foradeviation of the c-axes from the cylinder axis = 10° the grid width was 1° and from 10° until 20° deviation the grid witdth was 2°. Neutrons 20000 r\ r\ 5 G M39 llx+FWHM=8.15° !J.x+FWHM=7.7° • 4.9° ll x+ FWHM = 7.95° 10000 I • 3.25° \ i \ ' _. __ ..... / .... .......... __ _ 70° so· go• 1oo• x 70° so• goo 1ooo x 71• 75• so• s5o eo• 95• 1oo• 1o5o 109• Fig. 3a: Cuts though the pole sphere of the central piece number 5 at the values <p = 0° and <p = 120°. At 2° polar distance 30° in <p correspond to 1 o on a big circle of the pole sphere. Fig. 3b: Sums of the (005) reflection in-tensities on small circles of the pole sphe-re around the cylinder axis of the YBaCuO cylinder. The variation of x was in the limits 70° < X < 1l0°. The Sirnu-lated misalignment of the scattering vec-tor = 0.45°. 6 Neutrons Neutrons 3000 2 000 1 000 j\ I\ mo i . \ } . • I I ' 3 000 M39 CJ 2i 2000 1 000 'I'= 60' M39 CJ 2i 70' 80' 90' 1 00' 11 0' X 70' 80' 90' 1 00' 11 0' X 70' Fig. 4a: Cuts through the pole sphere of piece nurober 2i between piece nurober 5 and boundary piece nurober 2. The cuts were perforrned at <p = 60° and at <p = 190°. Neutrons Neutrons ~\ 4000 f. Center at 4000 x= 90.35' I. ßx= 4.6' i ßx = 3.9' 3.8' ~FWHM=4.0' 4 . \ FWHM = 3.8' 2000 I liJ M 39 2000 - r \ 'I' = 120· I . liJ M 39 ) 'I' = 330' r .... • X 70' 80' 90' 100' 110" 70' 80' 90' 100' 110' Fig. 5a: Cuts through the pole sphere of the boundary piece nurober 2 at <p = 120° and <p = 330°. X 80' 90' ll.x+ FWHM = 7.55' M39 D2i ll.x+ FWHM = 7.7' 100' X 110' Fig. 4b: Sums of the (005) reflection in-tensities on srnall circles around the cylin-der axis for piece nurober 2i. By calcula-ting the rnean values the sirnulated rnisa-lignrnent of the scattering vector was eli-rninated. This sirnulated and apparent rnisalignrnent was caused by a non-constant intensity over the vertical diver-gence of the neutron bearn. Neutrons / ;~"\ 20 000 I \ . ll.x+FWHM=8.9'• \ m• \ äHFWHM=9.7' 0 M39 4.6 • 4'6, • J ll. x+ FWHM = 9.3' 10 000 I 1. 5.1' \ .i . . \ I \I . . \. __ 75' 80' 90' 100' 105' Fig. 5b: Sums of the (005) reflection in-tensities on srnall circles around the cylin-der axis of the cylindric YBaCuO speci-rnen M 39. The rnean values f1X + FWHM produced in different ways differ only by 0.05°. Neutrons 1500-' 1500-1000-500-1\MW M . i \r) .!. • 7o• so• go• 1oo• 110• X Fig. 6a: Cuts through the pole sphere of the boundary piece number 1a at <p = 150° and <p = 330°. Neutrons 1500-1 000 5oo-7o· Neutrons 1 500-1 000-500-70° l~ i~ • I \ .! \ "' = 35o• so• 1bo 11o•x r_ .. I öx = 6.45. .~c·•~x ·"·"' ~\ I . l \ "' = 130° I -so• go• 1 oo• 111 o• x Fig. 7 a: Cuts through the pole sphere of the boundary piece number 3a of speci-men M 39. This boundary piece has still a clean texture. 7 Neutrons 5000 M39 .LJ 1a X 1100 Fig. 6b: Sums of the (005) reflection in-tensities on small circles of the pole sphe-re araund the cylinder axis of the YBaCuO specimen M 39. Only by sum-mations of the reflection intensity values on small circles of the pole sphere the distribution of the angular deviations of the c-axes from the cylinder axis becomes pronounced. Neutrons llx+ FWHM = 11.35° 1::::::::. 3a f\ f\ / \ 11.1° Lfi' ~ • 4.2° 7 500 5 000 11.6° ; 6( 17.4°; • 2500 J \ __,. \ / /'\ ·-·-· ' ,.. ·-· 75• so• s5• go• 95• 1 oo• 1 o5• x Fig. 7b: Distribution of angular deviations of the c-axes from the cylinder axis for piece number 3a. In cantrast to the boun-dary piece number 1a, the boundary piece number 3a shows a value for LlX + FWHM = 11.35°. This texture is still cle-an. Neutrons 3000-2000 1 000-I I I Center i\ r~ir~ !t\• FWHM = 3.4° '\ • tJ.x=5.7° ,. . \ . . 04----T~~~'-r---+~------2 000- \i FWHM=4.4° tJ.x = 3.4° 1 000- J ' ~ M39 I . ~ tp = 330° 0 .l 7o• so· 9o· 100° 110• X Fig. 8a: Cuts through the pole sphere of piece number 3, neighbour of the boun-dary piece number 3a. The medium bet-ween distribution maxima has the value x = 90.5°. That means that the simulated misalignment of the scattering vector is 0.5°. 7500- Neutrons i\ !J. X+ FWHM 5000- /4.4°\ ;----:--\1 • 11 5• 2500- ;" 7.1• \. · ~3a 0 ... /· • ...-• ......_,_. • 20 ooo- /\ 10• w 1 x-f 1 - I :, .... •5.5° \ 10000 • I \ 10.65° 0 3 _ I 5.15.,, ,· '• ...... _._ Q ~ I 20 ooo- i \ 10• w I x-f I - i r~ 10000 / \ 9.25° 02 - j 4.55~ ........ , 0 ........ 20 ooo- ( \ -n:4.7° 10 000 •• - 3.25\ '• o • ,--~- I I 10° 15° 7.95° lx-f I 8 Neutrons 0JM39 20 000 Fig. Sb: Sums of the (005) reflection in-tensities on small circles of the pole sphe-re of piece number 3 of specimen M 39. The difference of the different mean value calculations for the value t:..x + FWHM is only 0.15° (see Fig. 9). Neutrons 15 000 10 000 5000 \ M39 D 2i !J.X + FWHM = 7.9• '• --·-· 04o.----.---,1o-.---~·-~·-~·~20~:~Ix~-~~ Neutrons 5 000 M39 U 1a Fig. 9: From the distribution for x < 90° and x > 90° for each value I x - 1t12l the mean value was calculated. The simulated and apparant misalignment of the scattering vector was elimi-nated by this procedure. The value llX + FWHM increases from piece 5 at center to piece 3a at the boundary. 

The influence of a seed crystal on the texture of a bulk YBaCuO specimen

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The influence of a seed crystal on the texture of a bulk YBaCuO specimen

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