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Progress in depositing MgB2 films on stainless steel substrate
Physica C 452 (2007) 6–10 www.elsevier.com/locate/physc
Progress in depositing MgB2 films on stainless steel substrate Fen Li, Tao Guo, Kaicheng Zhang, Chinping Chen, Qing-rong Feng
*
Department of Physics and State Key Laboratory for Artificial Structure and Mesoscopic Physics, Peking University, Beijing 100871, PR China Received 9 September 2006; received in revised form 20 October 2006 Available online 10 January 2007
Abstract We have made a progress in fabricating MgB2 films, 25 lm, on the stainless steel substrate by hybrid physical–chemical vapor deposition. The superconducting transition temperature is, TC (onset) = 39.6 K with a transition width, DT = 0.5 K. The characterization by scanning electron microscope and X-ray diffraction indicates that its structure is polycrystalline. At T = 0 K, the upper critical field HC2 is determined as 15.2 T by extrapolation from a polynomial fitting to the transition temperatures under various applied fields, TC(H). In the self field, the critical current density JC is determined as 3.74 MA/cm2 at T = 15 K by a magnetic measurement according to the Bean model. 2006 Elsevier B.V. All rights reserved. PACS: 74.70.Ad; 74.76.w Keywords: MgB2 films; Stainless steel substrate; Upper critical field; Critical current; HPCVD
1. Introduction Since the discovery of the superconductivity in the simple binary compound MgB2 [1], tremendous research activities have burst out, concentrating on the study of this material. The interest lies in two folds. One is dedicated to understanding its various properties, such as the thermoelectric power [2,3], the critical field property [4], the transport properties [5–7], the dielectric property [8], the doping effect [9,10], the isotope effect [11], the proton irradiation effect [12], and the specific heat [13,14], etc. The other is aiming at seeking a less complicated process and yet efficient enough for a mass production of high quality wires, tapes etc., toward large scale applications. The advantage with MgB2 is apparent. In comparison with the conventional low-TC superconductors, i.e., Nb, Nb3Sn, etc., MgB2 has a much higher TC and larger energy gap, which means a potentially higher speeds. Increasing the operation temperature from 5 K for Nb to 20 K for MgB2 is a ‘‘big *
Corresponding author. Fax: +0086 10 62751615. E-mail address: [email protected] (Q.-r. Feng).
0921-4534/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2006.11.008
deal’’. A MgB2 technology with a high speed and an operation temperature at 20 K, using a much cheaper and much reliable cryocooler in comparison with those infrastructures necessary for the operation at 5 K using liquid helium, will make superconducting electronics much more competitive. Various techniques have been applied, including PIT [15–18], diffusion of Mg vapor into B-fiber [19], etc., in an effort to find out an effective and efficient process to produce the superconducting elements such as wires, tapes etc. Modest successes have been achieved. However, alternative approaches in looking for an easier and more efficient process are still under intensive studies in the laboratories. One of the routes may rely on the fabrication of thick films on various metal substrates as a pre-stage toward a mass production process of these superconducting elements. In particular, the deposition of MgB2 films on the normally available metal surface, such as the stainless steel or copper surface, is a significant step in technology. In this report, we demonstrate the deposition of MgB2 films over the stainless steel substrate with decent superconducting properties.
F. Li et al. / Physica C 452 (2007) 6–10
2. Experimental Experimentally, the setup for the synthesis process is uncomplicated, similar to that reported previously [20]. The reaction chamber is a quartz tube, inside which the vapor deposition process takes place. A gas mixture of 75% B2H6 in H2 and several pieces of pure Mg ingots serve as the active sources. The Mg ingots are first placed surrounding the iron sample holder inside the chamber. The iron sample holder can be heated up inductively by an rfgenerator to vaporize the Mg. The substrate is placed on top of the sample holder, which is supported by a columnar graphite with a large thermal capacity, so the temperature stability is more easily controlled. Additional pure gas of H2 also flows in the reaction chamber, serving to reduce the oxygen content and suppress any possible further oxidation of the sample during the deposition process. Furthermore, the H2 would cut down the decomposition rate of B2H6. The flow rate of the B2H6 mixture gas was about 10 sccm at a pressure of 2 kPa, and the background gas, H2, was about 100 sccm at 20 kPa. With the parameters of the flowing gases and the mass of Mg vaporized, the molar flow rate for B2H6 and Mg near the substrate can be estimated. The Mg flux is estimated about 5.3 · 105 mole/s, and B2H6, 1.0 · 107 mole/s. The background flow rate of H2 is 1.4 · 105 mole/s. So the reaction condition is Mg-rich environment. The temperature of the chamber was controlled within the range of 680–
7
720 C. With these parameters for the fabrication, the deposition rate reaches the level of 5–6 nm/s. according to the volume of MgB2 film formed in the platform, there was about 18% of B2H6 decomposing to participate the reaction. It is worth noting that one has to pay a special attention to the safety issue in handling the toxical B2H6 gas, in particular, at an explosive concentration 75%. The source tank is always stored in a refrigerator, with the interconnecting tubing running in a room temperature to the reaction chamber. The vacuum sealed is critical to prevent oxygen from getting into the system, also to avoid the toxical gas from leaking out of the system. A detector is installed in the laboratory to detect any possible leakage. No residual gas is allowed to stay in the tubing after each run. 3. Results and discussion The SEM observations were carried out on two samples, S1 and S2, by the FEI QUANTA 200 FEG scanning electron microscope. In Fig. 1(a) and (b) are for the surface morphology of S1, while (c) and (d), for S2. As shown in (b) and (d), the crystallites are almost the same in the size, 300–400 nm for both samples. However, the crystallites in (b) for S1 are more densely deposited than those in (d) for S2, as shown by the smaller gap between the crystallites in (b). In addition, the orientation of the crystallites
Fig. 1. SEM images for the MgB2 films on stainless steel substrates; (a) and (b) are for the morphology of S1. The magnification is 8000 with (a) and 60,000 with (b), respectively; (c) and (d) show the morphologies of S2 with the magnification of 6500 and 50,000, respectively.
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F. Li et al. / Physica C 452 (2007) 6–10
appears to be more aligned with S1 in (a) and (b), than with S2 in (c) and (d). This is obvious from the distribution in brightness of the crystallites. A more shining shade usually corresponds to a larger tilted angle of the crystallite surface from a horizontal position. A close inspection on the SEM photos reveals that some cracks exist with S2 in (c), whereas not a single crack is observed with S1 shown in (a). In a previous experiment, thick MgB2 film, 40 lm, has been grown on Al2O3 substrate [21]. Not a single cracks showed up. Obviously, the formation of the crack is not correlated with the thickness. It is very likely attributed to the mismatch of thermal expansion coefficient between the MgB2 film and the stainless steel substrate. As the temperature decreasing rate exceeds a certain limit, cracks occur in the film. This is further confirmed by the R–T measurement, in which the resistance does not drop to zero at a temperature below the transition temperature. It indicates that the cracks actually make a physically discontinuous separation of the film. The XRD analysis was performed using a Philip X’pertMRD diffractometer. The XRD spectrum for S1 is shown in Fig. 2. In addition to the main peaks of MgB2 by the index (1 0 1), (0 0 2), and (2 0 1), there are two weak MgO peaks showing up in the spectrum. It suggests that the film is comparatively clean. The broad peak around 23 is due to the poorly crystallized B [22], possibly related to the high concentration, high flux and correspondingly high decomposition rate of B2H6. The characteristic peaks of the substrate do not appear on the spectrum because the film thickness, 25 lm, exceeds the typical X-ray penetration length, a few micrometers. The B2H6 (75%) used in the present work is higher in concentration than that (25%) employed in the past. This may affect the crystal growth since the MgB2 film thus grown is not highly (1 0 1)-oriented as the one synthesized previously [23]. The temperature-dependent resistivity (q–T curve) for S1 was performed by a standard 4-probe measurement using a Quantum Design PPMS-9 System. The result is plotted in Fig. 3. The transition temperatures are determined as TC (onset) = 39.6 K and TC (zero) = 39.1 K. In the normal state, the resistivity is 3.70 lX cm at room temperature and it decreases to 2.38 lX cm at the transition
Fig. 2. XRD spectrum for the MgB2 film labeled as S1.
Fig. 3. q–T curve for the MgB2 film of S1.
temperature of 39.6 K. This is comparable to the value of the clean MgB2 film grown on graphite reported by Zhang et al. [24]. However, for the R–T curve of S2 not shown here, the resistance at T < TC does not drop to 0 X. This is correlated to the presence of cracks in the film, shown in Fig. 1(c). It strongly suggests that the superconductivity is not continuous across the film, attributed to the cracks in the film. The upper critical field HC2(T) of S1, shown in Fig. 4, is determined from the q–T measurements under applied fields up to 8 T shown in the inset of Fig. 4. By applying the polynomial HC2(T) = HC2(0) + A1T + A2T 2 + A3T 3 to fit the data points and extrapolating to T = 0 K, we obtain HC2(0) = 15.2 T. Fig. 4 shows that HC2(T) is curved upwards near TC. This agrees with the results reported previously [24,25]. Due to the small quantity of MgO impurities, HC2(0) for the present sample is not very high in comparison with that obtained for MgB2 films electroplated to a stainless steel substrate [26] and deposited on a silicon carbide substrate [27]. A series of M–H measurements on S1 were carried out with the applied magnetic field H parallel to the film surface using a quantum design SQUID magnetometer, MPMS-7. The results are plotted in the inset of Fig. 5. In low applied magnetic field, especially in the region of 0.02–4.7 kOe at T = 5 K and 0.02–2.2 kOe at T = 10 K indicated by the arrows, a phenomena of flux jump occurs.
Fig. 4. Upper critical field HC2(T) for S1. The inset is the q–T measurements under the applied fields up to 8 T. The numbers by the side of each curve in the inset stands for the applied field in unit of Tesla.
F. Li et al. / Physica C 452 (2007) 6–10
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(2 0 1) and c-axis. Its TC (onset) is about 39.6 K, and the transition width, 0.5 K. The upper critical field HC2(0) is extrapolated to T = 0 K as 15.2 T by a best polynomial fit. The critical current density JC is estimated by the Bean model as 3.74 MA/cm2 to 1.87 MA/cm per unit width of the film at 15 K in the zero field. These results indicate again that the HPCVD method is an appropriate technique to grow MgB2 films. Acknowledgement Fig. 5. Critical current density JC of S1 at T = 5, 10, 15 K derived from a series of M–H measurements shown in the inset. In the inset, the dashed line with a finite slope is for the signal of stainless steel substrate. The M– H measurements are carried out with the applied magnetic field H parallel to the film surface. The numbers in the figure indicate the temperature in unit of Kelvin.
This work is supported by NSFC under Contract No. 50572001. We appreciated the technical supports of Chen Li, Zhang Yan and Wang Yong-zhong. References
This is related to the very fine disorder structure and the relatively small thermal diffusion in the films at low temperature [28]. The slope of the dashed line is about 0.028 emu/T, origining from the magnetization of the stainless steel substrate itself. The derived critical current density JC according to the Bean model is shown in Fig. 5 as a function of the applied magnetic field H at T = 5, 10, and 15 K. Since the sample has a rectangular rather than circular cross section, we use a generalization of the original Bean formula [29]. For a sample of rectangular cross section 2a1 · 2a2 where a1 > a2, the magnetization is given by a2 a2 M ¼ JC 1 ; ð1Þ 20 3a1 where JC is the critical magnetization current in A/cm2, M is the magnetization in emu/cm3, and a1, a2 are in cm. In the present work, the applied field is parallel to the film, the relevant dimensions are the thickness and width of the film, that is a1 = 0.50 cm, a2 = 2.5 · 103 cm. For a2 a1, the formula (1) reduces to the original Bean formula for a semi-infinite slab [30], J C ¼ 20
M : a2
ð2Þ
For this sample, V = a3 * a1 * a2 = 0.65 * 0.50 * 2.5 · 103 cm3. With this value, M, hence, JC can be calculated by Eq. (2). In the zero field, JC is 3.74 MA/cm2 at T = 15 K, equivalent to a current density per unit width of the film, 1.87 MA/cm. With the applied field H = 2 kOe, JC is 3.65 MA/cm2 at T = 10 K. With H = 7.5 kOe, JC is 1.78 MA/cm2 at T = 5 K. These values are comparable to the previously reported JC [18,27,31]. In conclusion, by varying the experimental parameters, we have successfully synthesized MgB2 film with improving properties on the stainless steel substrate in comparison with the previously reported result [23]. The film is dense and highly textured with crystallization axis along (1 0 1)
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Progress in depositing MgB2 films on stainless steel substrate Fen Li, Tao Guo, Kaicheng Zhang, Chinping Chen, Qing-rong Feng
*
Department of Physics and State Key Laboratory for Artificial Structure and Mesoscopic Physics, Peking University, Beijing 100871, PR China Received 9 September 2006; received in revised form 20 October 2006 Available online 10 January 2007
Abstract We have made a progress in fabricating MgB2 films, 25 lm, on the stainless steel substrate by hybrid physical–chemical vapor deposition. The superconducting transition temperature is, TC (onset) = 39.6 K with a transition width, DT = 0.5 K. The characterization by scanning electron microscope and X-ray diffraction indicates that its structure is polycrystalline. At T = 0 K, the upper critical field HC2 is determined as 15.2 T by extrapolation from a polynomial fitting to the transition temperatures under various applied fields, TC(H). In the self field, the critical current density JC is determined as 3.74 MA/cm2 at T = 15 K by a magnetic measurement according to the Bean model. 2006 Elsevier B.V. All rights reserved. PACS: 74.70.Ad; 74.76.w Keywords: MgB2 films; Stainless steel substrate; Upper critical field; Critical current; HPCVD
1. Introduction Since the discovery of the superconductivity in the simple binary compound MgB2 [1], tremendous research activities have burst out, concentrating on the study of this material. The interest lies in two folds. One is dedicated to understanding its various properties, such as the thermoelectric power [2,3], the critical field property [4], the transport properties [5–7], the dielectric property [8], the doping effect [9,10], the isotope effect [11], the proton irradiation effect [12], and the specific heat [13,14], etc. The other is aiming at seeking a less complicated process and yet efficient enough for a mass production of high quality wires, tapes etc., toward large scale applications. The advantage with MgB2 is apparent. In comparison with the conventional low-TC superconductors, i.e., Nb, Nb3Sn, etc., MgB2 has a much higher TC and larger energy gap, which means a potentially higher speeds. Increasing the operation temperature from 5 K for Nb to 20 K for MgB2 is a ‘‘big *
Corresponding author. Fax: +0086 10 62751615. E-mail address: [email protected] (Q.-r. Feng).
0921-4534/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2006.11.008
deal’’. A MgB2 technology with a high speed and an operation temperature at 20 K, using a much cheaper and much reliable cryocooler in comparison with those infrastructures necessary for the operation at 5 K using liquid helium, will make superconducting electronics much more competitive. Various techniques have been applied, including PIT [15–18], diffusion of Mg vapor into B-fiber [19], etc., in an effort to find out an effective and efficient process to produce the superconducting elements such as wires, tapes etc. Modest successes have been achieved. However, alternative approaches in looking for an easier and more efficient process are still under intensive studies in the laboratories. One of the routes may rely on the fabrication of thick films on various metal substrates as a pre-stage toward a mass production process of these superconducting elements. In particular, the deposition of MgB2 films on the normally available metal surface, such as the stainless steel or copper surface, is a significant step in technology. In this report, we demonstrate the deposition of MgB2 films over the stainless steel substrate with decent superconducting properties.
F. Li et al. / Physica C 452 (2007) 6–10
2. Experimental Experimentally, the setup for the synthesis process is uncomplicated, similar to that reported previously [20]. The reaction chamber is a quartz tube, inside which the vapor deposition process takes place. A gas mixture of 75% B2H6 in H2 and several pieces of pure Mg ingots serve as the active sources. The Mg ingots are first placed surrounding the iron sample holder inside the chamber. The iron sample holder can be heated up inductively by an rfgenerator to vaporize the Mg. The substrate is placed on top of the sample holder, which is supported by a columnar graphite with a large thermal capacity, so the temperature stability is more easily controlled. Additional pure gas of H2 also flows in the reaction chamber, serving to reduce the oxygen content and suppress any possible further oxidation of the sample during the deposition process. Furthermore, the H2 would cut down the decomposition rate of B2H6. The flow rate of the B2H6 mixture gas was about 10 sccm at a pressure of 2 kPa, and the background gas, H2, was about 100 sccm at 20 kPa. With the parameters of the flowing gases and the mass of Mg vaporized, the molar flow rate for B2H6 and Mg near the substrate can be estimated. The Mg flux is estimated about 5.3 · 105 mole/s, and B2H6, 1.0 · 107 mole/s. The background flow rate of H2 is 1.4 · 105 mole/s. So the reaction condition is Mg-rich environment. The temperature of the chamber was controlled within the range of 680–
7
720 C. With these parameters for the fabrication, the deposition rate reaches the level of 5–6 nm/s. according to the volume of MgB2 film formed in the platform, there was about 18% of B2H6 decomposing to participate the reaction. It is worth noting that one has to pay a special attention to the safety issue in handling the toxical B2H6 gas, in particular, at an explosive concentration 75%. The source tank is always stored in a refrigerator, with the interconnecting tubing running in a room temperature to the reaction chamber. The vacuum sealed is critical to prevent oxygen from getting into the system, also to avoid the toxical gas from leaking out of the system. A detector is installed in the laboratory to detect any possible leakage. No residual gas is allowed to stay in the tubing after each run. 3. Results and discussion The SEM observations were carried out on two samples, S1 and S2, by the FEI QUANTA 200 FEG scanning electron microscope. In Fig. 1(a) and (b) are for the surface morphology of S1, while (c) and (d), for S2. As shown in (b) and (d), the crystallites are almost the same in the size, 300–400 nm for both samples. However, the crystallites in (b) for S1 are more densely deposited than those in (d) for S2, as shown by the smaller gap between the crystallites in (b). In addition, the orientation of the crystallites
Fig. 1. SEM images for the MgB2 films on stainless steel substrates; (a) and (b) are for the morphology of S1. The magnification is 8000 with (a) and 60,000 with (b), respectively; (c) and (d) show the morphologies of S2 with the magnification of 6500 and 50,000, respectively.
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F. Li et al. / Physica C 452 (2007) 6–10
appears to be more aligned with S1 in (a) and (b), than with S2 in (c) and (d). This is obvious from the distribution in brightness of the crystallites. A more shining shade usually corresponds to a larger tilted angle of the crystallite surface from a horizontal position. A close inspection on the SEM photos reveals that some cracks exist with S2 in (c), whereas not a single crack is observed with S1 shown in (a). In a previous experiment, thick MgB2 film, 40 lm, has been grown on Al2O3 substrate [21]. Not a single cracks showed up. Obviously, the formation of the crack is not correlated with the thickness. It is very likely attributed to the mismatch of thermal expansion coefficient between the MgB2 film and the stainless steel substrate. As the temperature decreasing rate exceeds a certain limit, cracks occur in the film. This is further confirmed by the R–T measurement, in which the resistance does not drop to zero at a temperature below the transition temperature. It indicates that the cracks actually make a physically discontinuous separation of the film. The XRD analysis was performed using a Philip X’pertMRD diffractometer. The XRD spectrum for S1 is shown in Fig. 2. In addition to the main peaks of MgB2 by the index (1 0 1), (0 0 2), and (2 0 1), there are two weak MgO peaks showing up in the spectrum. It suggests that the film is comparatively clean. The broad peak around 23 is due to the poorly crystallized B [22], possibly related to the high concentration, high flux and correspondingly high decomposition rate of B2H6. The characteristic peaks of the substrate do not appear on the spectrum because the film thickness, 25 lm, exceeds the typical X-ray penetration length, a few micrometers. The B2H6 (75%) used in the present work is higher in concentration than that (25%) employed in the past. This may affect the crystal growth since the MgB2 film thus grown is not highly (1 0 1)-oriented as the one synthesized previously [23]. The temperature-dependent resistivity (q–T curve) for S1 was performed by a standard 4-probe measurement using a Quantum Design PPMS-9 System. The result is plotted in Fig. 3. The transition temperatures are determined as TC (onset) = 39.6 K and TC (zero) = 39.1 K. In the normal state, the resistivity is 3.70 lX cm at room temperature and it decreases to 2.38 lX cm at the transition
Fig. 2. XRD spectrum for the MgB2 film labeled as S1.
Fig. 3. q–T curve for the MgB2 film of S1.
temperature of 39.6 K. This is comparable to the value of the clean MgB2 film grown on graphite reported by Zhang et al. [24]. However, for the R–T curve of S2 not shown here, the resistance at T < TC does not drop to 0 X. This is correlated to the presence of cracks in the film, shown in Fig. 1(c). It strongly suggests that the superconductivity is not continuous across the film, attributed to the cracks in the film. The upper critical field HC2(T) of S1, shown in Fig. 4, is determined from the q–T measurements under applied fields up to 8 T shown in the inset of Fig. 4. By applying the polynomial HC2(T) = HC2(0) + A1T + A2T 2 + A3T 3 to fit the data points and extrapolating to T = 0 K, we obtain HC2(0) = 15.2 T. Fig. 4 shows that HC2(T) is curved upwards near TC. This agrees with the results reported previously [24,25]. Due to the small quantity of MgO impurities, HC2(0) for the present sample is not very high in comparison with that obtained for MgB2 films electroplated to a stainless steel substrate [26] and deposited on a silicon carbide substrate [27]. A series of M–H measurements on S1 were carried out with the applied magnetic field H parallel to the film surface using a quantum design SQUID magnetometer, MPMS-7. The results are plotted in the inset of Fig. 5. In low applied magnetic field, especially in the region of 0.02–4.7 kOe at T = 5 K and 0.02–2.2 kOe at T = 10 K indicated by the arrows, a phenomena of flux jump occurs.
Fig. 4. Upper critical field HC2(T) for S1. The inset is the q–T measurements under the applied fields up to 8 T. The numbers by the side of each curve in the inset stands for the applied field in unit of Tesla.
F. Li et al. / Physica C 452 (2007) 6–10
9
(2 0 1) and c-axis. Its TC (onset) is about 39.6 K, and the transition width, 0.5 K. The upper critical field HC2(0) is extrapolated to T = 0 K as 15.2 T by a best polynomial fit. The critical current density JC is estimated by the Bean model as 3.74 MA/cm2 to 1.87 MA/cm per unit width of the film at 15 K in the zero field. These results indicate again that the HPCVD method is an appropriate technique to grow MgB2 films. Acknowledgement Fig. 5. Critical current density JC of S1 at T = 5, 10, 15 K derived from a series of M–H measurements shown in the inset. In the inset, the dashed line with a finite slope is for the signal of stainless steel substrate. The M– H measurements are carried out with the applied magnetic field H parallel to the film surface. The numbers in the figure indicate the temperature in unit of Kelvin.
This work is supported by NSFC under Contract No. 50572001. We appreciated the technical supports of Chen Li, Zhang Yan and Wang Yong-zhong. References
This is related to the very fine disorder structure and the relatively small thermal diffusion in the films at low temperature [28]. The slope of the dashed line is about 0.028 emu/T, origining from the magnetization of the stainless steel substrate itself. The derived critical current density JC according to the Bean model is shown in Fig. 5 as a function of the applied magnetic field H at T = 5, 10, and 15 K. Since the sample has a rectangular rather than circular cross section, we use a generalization of the original Bean formula [29]. For a sample of rectangular cross section 2a1 · 2a2 where a1 > a2, the magnetization is given by a2 a2 M ¼ JC 1 ; ð1Þ 20 3a1 where JC is the critical magnetization current in A/cm2, M is the magnetization in emu/cm3, and a1, a2 are in cm. In the present work, the applied field is parallel to the film, the relevant dimensions are the thickness and width of the film, that is a1 = 0.50 cm, a2 = 2.5 · 103 cm. For a2 a1, the formula (1) reduces to the original Bean formula for a semi-infinite slab [30], J C ¼ 20
M : a2
ð2Þ
For this sample, V = a3 * a1 * a2 = 0.65 * 0.50 * 2.5 · 103 cm3. With this value, M, hence, JC can be calculated by Eq. (2). In the zero field, JC is 3.74 MA/cm2 at T = 15 K, equivalent to a current density per unit width of the film, 1.87 MA/cm. With the applied field H = 2 kOe, JC is 3.65 MA/cm2 at T = 10 K. With H = 7.5 kOe, JC is 1.78 MA/cm2 at T = 5 K. These values are comparable to the previously reported JC [18,27,31]. In conclusion, by varying the experimental parameters, we have successfully synthesized MgB2 film with improving properties on the stainless steel substrate in comparison with the previously reported result [23]. The film is dense and highly textured with crystallization axis along (1 0 1)
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