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Single Crystals Sr14-xCaxCu24O41 Grown under Different Oxygen Pressures by Optical Floating-Zone Technique
Rare Metal Materials and Engineering Volume 40, Issue 11, November 2011 Online English edition of the Chinese language journal Cite this article as: Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900.
ARTICLE
Single Crystals Sr14-xCaxCu24O41 Grown under Different Oxygen Pressures by Optical Floating-Zone Technique Wang Qingbo1, 1
Zhou Cui2,
Tao Qian3,
Xu Zhu’an3 2
3
China University of Geosciences (Wuhan), Wuhan 430074，China; Air Force Radar Academy, Wuhan 430019, China; Zhejiang University,
Hangzhou 310027, China
Abstract: Spin ladder compounds Sr14-xCaxCu24O41 (SCCO) single crystals have been grown under different oxygen pressures by an optical floating-zone technique. The effects of oxygen pressure on the crystal growth and properties of SCCO were studied. The SCCO single crystals with x≤8 can be grown in a flowing oxygen atmosphere. But the growth of the SCCO compounds with higher Ca content (x>8) needs higher pressure (0.9 MPa). The single crystals were characterized by means of XRD, EDX and resistivity measurement. High pressure is in favor of forming of higher Ca-doped SCCO single crystals. SCCO single crystals grown under different oxygen pressures have almost the same quality. Key words: crystal growth; optical floating-zone technique; oxygen pressure; spin ladder compound
Spin ladder compound Sr14-xCaxCu24O41 (SCCO) shows fascinating transport and magnetic properties[1]. The discovery of the superconductivity in Sr0.4Ca13.6Cu24O41 under high pressure is striking[2]. The result is regarded as realizing of the remarkable theoretical prediction of superconductivity in two-leg doped spin ladder [1, 3-5]. A parent compound Sr14Cu24O41 crystallizes in the Cccm space group. Its lattice parameters are a=1.1469 nm, b=1.3400 nm and c=2.7650 nm. The lattice parameters decrease gradually with increasing of Ca content because of their different ion radii. The average Cu valence of the parent compound Sr14Cu24O41 is +2.25, which means there are six holes per formula unit (f.u.). So, it is already intrinsical hole doped without any substitution. But it is insulated because the holes are localized. Experiment and theory experts have suggested that the holes are localized in chains and only one hole per f.u. is located on ladders. Some holes transfer to ladders if Ca substitutes on Sr sites [6-9]. The number of total holes is unchanged because Sr and Ca ions are isovalent. But the mobility of holes is increased. As a result, the spin ladder compound system becomes more metallic. Single crystals are important in studying their properties. In
crystal growth methods, the flux method is important [10,11]. Noji et al. grew the Sr14-xCaxCu24O41 (x=0, 6.8) single crystals using NaCl as the flux medium. But the crystals were thin. Their sizes were 1 mm×0.05 mm×1.5 mm and 0.3 mm×0.05 mm×2 mm[12]. In some experiments, the size of crystals is important such as an inelastic neutron scattering. Fortunately, an optical floating-zone method provides a possible way to prepare larger crystals[13-15]. Using the method, Ammerahl et al. grew a series of lager Sr14-xCaxCu24O41 (SCCO) single crystals under high-oxygen pressure (0.3-0.8 MPa)[16]. However, pressure equipment is absent in some places and dangerous to operators. To our knowledge, the research of preparing of a series of SCCO single crystals under flowing oxygen (0.1 MPa) by an optical floating-zone method is fewer. The purpose of the investigation is to prepare a series of SCCO single crystals under different oxygen pressures by an optical floating-zone technique. The difference of the crystals is also studied.
1
Experiment
First, single-phase SCCO polycrystalline powder was prepared using a conventional solid-state reaction method. The
Received date: March 12, 2011 Foundation item: Special Foundation for Basic Scientific Research of Central Colleges, China University of Geosciences (Wuhan) (CUGL110236); National Natural Science Foundation of China (41104054, 61008054) Corresponding author: Wang Qingbo, Ph. D., Lecturer, School of Mathematics and Physics, China University of Geosciences (Wuhan), Wuhan 430074, P. R. China, Tel: 0086-27-67883091, E-mail: [email protected] Copyright © 2011, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.
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Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
Ellipsoidal reflector
Crystal Seed rod
Halogen lamp
Fig.1 Scheme of a single crystal rod growth furnace
Fig.2 A typical single crystal rod grown by the optical floating-zone technique
060
020
Intensity/a.u.
080
040
a
x=8 x=6 x=4 x=0
10
20 30
40 50
60 70 80
b
060
080
040
2θ/(º)
020
10
x=11 x=10 x=8 x=6 x=4 x=2 x=0
20 30
40 50
60 70 80
2θ/(º)
2 Results and Discussion
c
1.34 1.32 b/nm
Fig.2 shows a typical single crystal grown by an optical floating-zone technique. Crystals are easily cleaved along the ac-plane as confirmed by XRD. Fig.3a and 3b show the X-ray diffraction patterns of the cleaved SCCO single crystals under different pressures. For different Ca doping contents, XRD patterns are basically the same, and only a little shift of reflection peaks is observed because of the small change of lattice constants. From XRD measurements, no impure phase is detected in the single crystals. We find that (0k0) peaks shift from a small angle to a larger angle monotonously, which is attributed to that the b-axis lattice parameter of Sr14-xCaxCu24O41 (SCCO) decreases with increasing of Ca
Feed rod
Molten zone
Intensity/a.u.
reaction equation is (14-x)SrCO3+xCaCO3+24CuO+1.5O2 →Sr14-xCaxCu24O41+14CO2. From the equation, we can see that the reaction needs to absorb oxygen. So, the sintering is easier in an oxygen atmosphere. SrCO3 (4N), CaCO3 (4N) and CuO (4N) powders were mixed with nominal chemical ratios and well ground using an agate ball mill. Then the mixture was heated at 850 °C for 24 h in air. The products were sintered at 950 °C for 24 h in a flowing oxygen atmosphere several times with intermediate grinding. The single-phase polycrystalline powder was pressed into cylindrical rods with a size of about 100 mm in length and 7 mm in diameter under 70 MPa. The rods were annealed at 950 °C for 24 h in a flowing oxygen atmosphere. High-quality SCCO single crystals were grown by an optical floating-zone technique. The furnace is a four-mirror optical floating-zone furnace (CSI System Inc.). It uses four halogen lamps with 300 W as the heating sources. Fig.1 shows a scheme of the crystal growth furnace. The crystals were grown in different atmospheres: a flowing oxygen atmosphere and high-pressure oxygen (0.4 and 0.9 MPa) atmospheres. A part of a rod was taken as a seed rod and the other part was used as a feed rod. The experiment could be carried out faster if crystals were grown with a single crystal seed rod. The crystal growth speed was 1 mm/h with a counter rotation of feed and seed rods at 30 r/min. It was easier to stabilize a molten zone under pressure. Crystals became single domain after 3 h. The typical dimension of the crystals was about 40 mm in length and 6 mm in diameter. The shapes of the crystals were elliptic and their colors were dark purple. The shape and color were observed by another experiment[16]. High quality crystals could be obtained from the top of crystals rods. A typical cleaved single crystal was 5 mm×5 mm×2 mm. An XRD analysis was carried out using a D/Max-rA diffractometer with Cu-Kα radiation and a graphite monochromator. An EDX analysis was performed on an EDAX GENESIS 4000 X-ray analysis system affiliated to an SEM (model SIRION). A standard DC four-probe method was used to measure the electrical resistivity of the crystals along the c-axis. All electrical transport measurements were performed in a Janis cryostat.
Flowing oxygen High pressure
1.30 1.28 1.26 0
2
4
6
8
10
Ca Content, x Fig.3 XRD patterns of the cleaved SCCO single crystals grown under different conditions: (a) in flowing oxygen, (b) under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11), and (c) the variation of the b-axis lattice constant with x
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Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
a
100 µm
Ratio of Ca/Sr
4
b
3
Flowing oxygen High pressure Theoretical ratio
2
2
4
6
8
10
Nominal Composition of Ca, x
Fig.4 SEM image of Sr10Ca4Cu24O41 single crystal grown in flowing oxygen(a). The Ca/Sr ratios of the crystals grown under the different conditions: in flowing oxygen, under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11) (b)
x=0 x=2 x=4 x=6 x=8
2
ρ/Ω·cm
10
101
a
100 10-1 10-2 0 103
100
200
300 x=0 x=2 x=4 x=6 x=8 x=10 x=11
102 101 100
b
10-1 10-2 0
60
120 180
240
300
T/K Fig.5 Temperature dependence of the electrical resistivities for the Sr14-xCaxCu24O41 single crystals grown under different conditions: (a) in flowing oxygen and (b) under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11)
to measure the DC resistivity of the c-axis. Fig.5 shows the temperature dependence of the electrical resistivity for SCCO along the c-axis. As reported in some papers[6, 7, 9], holes’ localization leads to an insulating behavior in a parent compound Sr14Cu24O41. The holes can be transferred from chains to ladders by Ca substitution. The conductivity increases with increasing of Ca content. The temperature dependence of the electrical resistivity is semiconductive behavior for the SCCO (x≤10) compounds. The resistivity decreases with increasing of the x in the SCCO single crystals. The resistivities of the crystals grown under high pressure are fewer than those grown in flowing oxygen. The fewer resistivities are ascribed to their more Ca contents. The result is compared well with the results of XRD and EDX. We can see that high pressure favors Ca substituting Sr in the SCCO single crystals. Besides a little difference of Ca content, the electrical resistivity curve shows evidence that crystals grown under different atmospheres are in good quality.
3
1 0 0
103
ρ/Ω·cm
content. We refined the lattice constants by a least-squares fit method. Fig.3c shows the varying b-axis lattice constant with x. We can see that b-axis lattice constant decreases linearly with increasing of Ca content x. The variation of the b-axis lattice parameter was also observed in another report[17]. The lattice parameters decrease with increasing of Ca content because the ion size of Ca is smaller than that of Sr. The b-axis lattice constants of the crystals grown under high-oxygen pressure are fewer than those grown under flowing oxygen (0.1 MPa) at the same Ca constant. The difference of b-axis lattice constant means that the crystals grown under high-oxygen pressure have higher Ca contents. To find the Ca content in the crystals, we used an EDX to estimate the composition of the single crystals. We performed a compositional analysis at different points on the crystals cleaved from the top of the crystal rods. There is a little variation in Ca/Sr ratios on the crystals. Fig.4a shows the SEM image of the surface of Sr10Ca4Cu24O41 crystal used for EDX. There are no defects and impurities on the surface of the crystal. Fig.4b presents the Ca/Sr ratios of the crystals. The results of EDX show that the chemical composition of the crystals is reasonably identical with the theoretical ratio. In general, the chemical composition of crystals is reasonably identical with that of the starting materials. The Ca content of the crystals grown under high pressure is more than those grown under a flowing oxygen atmosphere. The result means that Ca is easier to substitute Sr under high pressure. The Ca content can affect the electrical resistivity. To examine how the preparation conditions affect the electrical resistivity of the crystals, we used a standard four-probe method
Conclusions
1) A series of high-quality Sr14-xCaxCu24O41 (SCCO) single crystals can be grown under different oxygen pressures. 2) High pressure is in favor of the formation of the higher Ca-doped SCCO single crystals. Besides a little different Ca content, the high-quality SCCO (x≤8) single crystals can be grown in flowing oxygen. The quality of these crystals is as good as those grown under high pressure. But the higher Ca content SCCO single crystals must be grown under high pressure.
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Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
References 1 Dagotto E. Rep Prog Phys[J], 1999, 62: 1525 2 Uehara M, Nagata T, Akimitsu J. J Phys Soc Jpn[J], 1996, 65: 2764 3 Dagotto E, Riera J, Scalapino D. Phys Rev B[J], 1992, 45: 5744 4 Sigrist M, Rice T M, Zhang F C. Phys Rev B[J], 1994, 49: 12 058 5 Tsunetsugu H, Troyer M, RiceT M. Phys Rev B[J], 1994, 49: 16 078 6 Nücker N, Merz M, Kuntscher C A. Phys Rev B[J], 2000, 62: 14 384 7 Osafune T, Motoyama N, Eisaki H. Phys Rev Lett[J], 1997, 78: 1980 8 Wang Q B, Xu X F, Tao Q. Chin Phys Lett[J], 2008, 25: 1857
155 122 10 Hong S H, Sato T, Mikami M. J Cryst Growth[J], 2009, 311: 3451 11 Nakachi Y, Ueda K. J Cryst Growth[J], 2008, 311: 114 12 Noji T, Kakimoto K, Koike Y. Jpn J Appl Phys Part 1 - Regul Pap Short Notes Rev Pap[J], 1998, 37: 100 13 Wizent N, Behr G, Lipps F. J Cryst Growth[J], 2009, 311: 1273 14 Wen J S, Xu Z J, Xu G Y. J Cryst Growth[J], 2008, 310: 1401 15 Hermann R, Vinzelberg H, Behr G. J Cryst Growth[J], 2008, 310: 4286 16 Ammerahl U, Dhalenne G, Revcolevschi A. J Cryst Growth[J], 1998, 193: 55 17 Kato M, Shiota K, Koike Y. Physica C[J], 1996, 258: 284
9 Tafra E, Korin-Hamzić B, Basletić M. Phys Rev B[J], 2008, 78:
1900
ARTICLE
Single Crystals Sr14-xCaxCu24O41 Grown under Different Oxygen Pressures by Optical Floating-Zone Technique Wang Qingbo1, 1
Zhou Cui2,
Tao Qian3,
Xu Zhu’an3 2
3
China University of Geosciences (Wuhan), Wuhan 430074，China; Air Force Radar Academy, Wuhan 430019, China; Zhejiang University,
Hangzhou 310027, China
Abstract: Spin ladder compounds Sr14-xCaxCu24O41 (SCCO) single crystals have been grown under different oxygen pressures by an optical floating-zone technique. The effects of oxygen pressure on the crystal growth and properties of SCCO were studied. The SCCO single crystals with x≤8 can be grown in a flowing oxygen atmosphere. But the growth of the SCCO compounds with higher Ca content (x>8) needs higher pressure (0.9 MPa). The single crystals were characterized by means of XRD, EDX and resistivity measurement. High pressure is in favor of forming of higher Ca-doped SCCO single crystals. SCCO single crystals grown under different oxygen pressures have almost the same quality. Key words: crystal growth; optical floating-zone technique; oxygen pressure; spin ladder compound
Spin ladder compound Sr14-xCaxCu24O41 (SCCO) shows fascinating transport and magnetic properties[1]. The discovery of the superconductivity in Sr0.4Ca13.6Cu24O41 under high pressure is striking[2]. The result is regarded as realizing of the remarkable theoretical prediction of superconductivity in two-leg doped spin ladder [1, 3-5]. A parent compound Sr14Cu24O41 crystallizes in the Cccm space group. Its lattice parameters are a=1.1469 nm, b=1.3400 nm and c=2.7650 nm. The lattice parameters decrease gradually with increasing of Ca content because of their different ion radii. The average Cu valence of the parent compound Sr14Cu24O41 is +2.25, which means there are six holes per formula unit (f.u.). So, it is already intrinsical hole doped without any substitution. But it is insulated because the holes are localized. Experiment and theory experts have suggested that the holes are localized in chains and only one hole per f.u. is located on ladders. Some holes transfer to ladders if Ca substitutes on Sr sites [6-9]. The number of total holes is unchanged because Sr and Ca ions are isovalent. But the mobility of holes is increased. As a result, the spin ladder compound system becomes more metallic. Single crystals are important in studying their properties. In
crystal growth methods, the flux method is important [10,11]. Noji et al. grew the Sr14-xCaxCu24O41 (x=0, 6.8) single crystals using NaCl as the flux medium. But the crystals were thin. Their sizes were 1 mm×0.05 mm×1.5 mm and 0.3 mm×0.05 mm×2 mm[12]. In some experiments, the size of crystals is important such as an inelastic neutron scattering. Fortunately, an optical floating-zone method provides a possible way to prepare larger crystals[13-15]. Using the method, Ammerahl et al. grew a series of lager Sr14-xCaxCu24O41 (SCCO) single crystals under high-oxygen pressure (0.3-0.8 MPa)[16]. However, pressure equipment is absent in some places and dangerous to operators. To our knowledge, the research of preparing of a series of SCCO single crystals under flowing oxygen (0.1 MPa) by an optical floating-zone method is fewer. The purpose of the investigation is to prepare a series of SCCO single crystals under different oxygen pressures by an optical floating-zone technique. The difference of the crystals is also studied.
1
Experiment
First, single-phase SCCO polycrystalline powder was prepared using a conventional solid-state reaction method. The
Received date: March 12, 2011 Foundation item: Special Foundation for Basic Scientific Research of Central Colleges, China University of Geosciences (Wuhan) (CUGL110236); National Natural Science Foundation of China (41104054, 61008054) Corresponding author: Wang Qingbo, Ph. D., Lecturer, School of Mathematics and Physics, China University of Geosciences (Wuhan), Wuhan 430074, P. R. China, Tel: 0086-27-67883091, E-mail: [email protected] Copyright © 2011, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.
1897
Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
Ellipsoidal reflector
Crystal Seed rod
Halogen lamp
Fig.1 Scheme of a single crystal rod growth furnace
Fig.2 A typical single crystal rod grown by the optical floating-zone technique
060
020
Intensity/a.u.
080
040
a
x=8 x=6 x=4 x=0
10
20 30
40 50
60 70 80
b
060
080
040
2θ/(º)
020
10
x=11 x=10 x=8 x=6 x=4 x=2 x=0
20 30
40 50
60 70 80
2θ/(º)
2 Results and Discussion
c
1.34 1.32 b/nm
Fig.2 shows a typical single crystal grown by an optical floating-zone technique. Crystals are easily cleaved along the ac-plane as confirmed by XRD. Fig.3a and 3b show the X-ray diffraction patterns of the cleaved SCCO single crystals under different pressures. For different Ca doping contents, XRD patterns are basically the same, and only a little shift of reflection peaks is observed because of the small change of lattice constants. From XRD measurements, no impure phase is detected in the single crystals. We find that (0k0) peaks shift from a small angle to a larger angle monotonously, which is attributed to that the b-axis lattice parameter of Sr14-xCaxCu24O41 (SCCO) decreases with increasing of Ca
Feed rod
Molten zone
Intensity/a.u.
reaction equation is (14-x)SrCO3+xCaCO3+24CuO+1.5O2 →Sr14-xCaxCu24O41+14CO2. From the equation, we can see that the reaction needs to absorb oxygen. So, the sintering is easier in an oxygen atmosphere. SrCO3 (4N), CaCO3 (4N) and CuO (4N) powders were mixed with nominal chemical ratios and well ground using an agate ball mill. Then the mixture was heated at 850 °C for 24 h in air. The products were sintered at 950 °C for 24 h in a flowing oxygen atmosphere several times with intermediate grinding. The single-phase polycrystalline powder was pressed into cylindrical rods with a size of about 100 mm in length and 7 mm in diameter under 70 MPa. The rods were annealed at 950 °C for 24 h in a flowing oxygen atmosphere. High-quality SCCO single crystals were grown by an optical floating-zone technique. The furnace is a four-mirror optical floating-zone furnace (CSI System Inc.). It uses four halogen lamps with 300 W as the heating sources. Fig.1 shows a scheme of the crystal growth furnace. The crystals were grown in different atmospheres: a flowing oxygen atmosphere and high-pressure oxygen (0.4 and 0.9 MPa) atmospheres. A part of a rod was taken as a seed rod and the other part was used as a feed rod. The experiment could be carried out faster if crystals were grown with a single crystal seed rod. The crystal growth speed was 1 mm/h with a counter rotation of feed and seed rods at 30 r/min. It was easier to stabilize a molten zone under pressure. Crystals became single domain after 3 h. The typical dimension of the crystals was about 40 mm in length and 6 mm in diameter. The shapes of the crystals were elliptic and their colors were dark purple. The shape and color were observed by another experiment[16]. High quality crystals could be obtained from the top of crystals rods. A typical cleaved single crystal was 5 mm×5 mm×2 mm. An XRD analysis was carried out using a D/Max-rA diffractometer with Cu-Kα radiation and a graphite monochromator. An EDX analysis was performed on an EDAX GENESIS 4000 X-ray analysis system affiliated to an SEM (model SIRION). A standard DC four-probe method was used to measure the electrical resistivity of the crystals along the c-axis. All electrical transport measurements were performed in a Janis cryostat.
Flowing oxygen High pressure
1.30 1.28 1.26 0
2
4
6
8
10
Ca Content, x Fig.3 XRD patterns of the cleaved SCCO single crystals grown under different conditions: (a) in flowing oxygen, (b) under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11), and (c) the variation of the b-axis lattice constant with x
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Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
a
100 µm
Ratio of Ca/Sr
4
b
3
Flowing oxygen High pressure Theoretical ratio
2
2
4
6
8
10
Nominal Composition of Ca, x
Fig.4 SEM image of Sr10Ca4Cu24O41 single crystal grown in flowing oxygen(a). The Ca/Sr ratios of the crystals grown under the different conditions: in flowing oxygen, under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11) (b)
x=0 x=2 x=4 x=6 x=8
2
ρ/Ω·cm
10
101
a
100 10-1 10-2 0 103
100
200
300 x=0 x=2 x=4 x=6 x=8 x=10 x=11
102 101 100
b
10-1 10-2 0
60
120 180
240
300
T/K Fig.5 Temperature dependence of the electrical resistivities for the Sr14-xCaxCu24O41 single crystals grown under different conditions: (a) in flowing oxygen and (b) under oxygen pressure of 0.4 MPa (x≤8) and 0.9 MPa (x=10, 11)
to measure the DC resistivity of the c-axis. Fig.5 shows the temperature dependence of the electrical resistivity for SCCO along the c-axis. As reported in some papers[6, 7, 9], holes’ localization leads to an insulating behavior in a parent compound Sr14Cu24O41. The holes can be transferred from chains to ladders by Ca substitution. The conductivity increases with increasing of Ca content. The temperature dependence of the electrical resistivity is semiconductive behavior for the SCCO (x≤10) compounds. The resistivity decreases with increasing of the x in the SCCO single crystals. The resistivities of the crystals grown under high pressure are fewer than those grown in flowing oxygen. The fewer resistivities are ascribed to their more Ca contents. The result is compared well with the results of XRD and EDX. We can see that high pressure favors Ca substituting Sr in the SCCO single crystals. Besides a little difference of Ca content, the electrical resistivity curve shows evidence that crystals grown under different atmospheres are in good quality.
3
1 0 0
103
ρ/Ω·cm
content. We refined the lattice constants by a least-squares fit method. Fig.3c shows the varying b-axis lattice constant with x. We can see that b-axis lattice constant decreases linearly with increasing of Ca content x. The variation of the b-axis lattice parameter was also observed in another report[17]. The lattice parameters decrease with increasing of Ca content because the ion size of Ca is smaller than that of Sr. The b-axis lattice constants of the crystals grown under high-oxygen pressure are fewer than those grown under flowing oxygen (0.1 MPa) at the same Ca constant. The difference of b-axis lattice constant means that the crystals grown under high-oxygen pressure have higher Ca contents. To find the Ca content in the crystals, we used an EDX to estimate the composition of the single crystals. We performed a compositional analysis at different points on the crystals cleaved from the top of the crystal rods. There is a little variation in Ca/Sr ratios on the crystals. Fig.4a shows the SEM image of the surface of Sr10Ca4Cu24O41 crystal used for EDX. There are no defects and impurities on the surface of the crystal. Fig.4b presents the Ca/Sr ratios of the crystals. The results of EDX show that the chemical composition of the crystals is reasonably identical with the theoretical ratio. In general, the chemical composition of crystals is reasonably identical with that of the starting materials. The Ca content of the crystals grown under high pressure is more than those grown under a flowing oxygen atmosphere. The result means that Ca is easier to substitute Sr under high pressure. The Ca content can affect the electrical resistivity. To examine how the preparation conditions affect the electrical resistivity of the crystals, we used a standard four-probe method
Conclusions
1) A series of high-quality Sr14-xCaxCu24O41 (SCCO) single crystals can be grown under different oxygen pressures. 2) High pressure is in favor of the formation of the higher Ca-doped SCCO single crystals. Besides a little different Ca content, the high-quality SCCO (x≤8) single crystals can be grown in flowing oxygen. The quality of these crystals is as good as those grown under high pressure. But the higher Ca content SCCO single crystals must be grown under high pressure.
1899
Wang Qingbo et al. / Rare Metal Materials and Engineering, 2011, 40(11): 1897-1900
References 1 Dagotto E. Rep Prog Phys[J], 1999, 62: 1525 2 Uehara M, Nagata T, Akimitsu J. J Phys Soc Jpn[J], 1996, 65: 2764 3 Dagotto E, Riera J, Scalapino D. Phys Rev B[J], 1992, 45: 5744 4 Sigrist M, Rice T M, Zhang F C. Phys Rev B[J], 1994, 49: 12 058 5 Tsunetsugu H, Troyer M, RiceT M. Phys Rev B[J], 1994, 49: 16 078 6 Nücker N, Merz M, Kuntscher C A. Phys Rev B[J], 2000, 62: 14 384 7 Osafune T, Motoyama N, Eisaki H. Phys Rev Lett[J], 1997, 78: 1980 8 Wang Q B, Xu X F, Tao Q. Chin Phys Lett[J], 2008, 25: 1857
155 122 10 Hong S H, Sato T, Mikami M. J Cryst Growth[J], 2009, 311: 3451 11 Nakachi Y, Ueda K. J Cryst Growth[J], 2008, 311: 114 12 Noji T, Kakimoto K, Koike Y. Jpn J Appl Phys Part 1 - Regul Pap Short Notes Rev Pap[J], 1998, 37: 100 13 Wizent N, Behr G, Lipps F. J Cryst Growth[J], 2009, 311: 1273 14 Wen J S, Xu Z J, Xu G Y. J Cryst Growth[J], 2008, 310: 1401 15 Hermann R, Vinzelberg H, Behr G. J Cryst Growth[J], 2008, 310: 4286 16 Ammerahl U, Dhalenne G, Revcolevschi A. J Cryst Growth[J], 1998, 193: 55 17 Kato M, Shiota K, Koike Y. Physica C[J], 1996, 258: 284
9 Tafra E, Korin-Hamzić B, Basletić M. Phys Rev B[J], 2008, 78:
1900