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1.
We previously reported on the discovery of new Pb-based 1222 cuprates containing boron in the (Pb0.5B0.5)Sr2(RE2−xy Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. However, none of the cuprates was a superconductor, but a semiconductor with the conduction process of a three-dimensional variable range hopping at low temperatures, despite annealing under O2 atmosphere at 100 atm and 400 °C. Recently, we have discovered that some samples showed superconductivity in the (Pb0.5B0.5)Sr2(Y1.9−x Ce x Sr0.1)Cu2O z system. Among them, the sample with x=0.45 shows the highest zero resistivity temperature at about 10 K and it shows a diamagnetic signal starting at abut 16 K with lowering temperature. The superconductivity is considered to originate from the 1222 phase.  相似文献   

2.
New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb0.75P0.25)Sr2- (RE2–xy Ce x Sr y )Cu2O z (RE = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single phase samples are obtained for 0.5≤x≤1.0 and y=0.1 in the cases of RE = Nd, Dy, Ho, Er, Tm, Yb and Y, while for 0.3≤x≤1.0 and y=0.1 in the cases of RE = Sm, Eu and Gd. The samples crystallize in a tetragonal lattice, the lattice parameters a and c are decreasing with the decrease of the ionic radius of the RE element. Even after annealing under 143 atm O2 atmosphere at 400 °C, almost all the samples with the common values x=0.5 and y=0.1 are semiconductors with a transport process followed by three-dimensional variable range hopping. However, the samples of RE = Sm, Eu and Gd, which are of almost single 1222 phase, even for x=0.3 and y=0.1, show superconductivity with the onsets at about 25 K, 20 K and 22 K, respectively. Through this study, we find very important procedure for discovery of new superconducting 1222 compound.  相似文献   

3.
New Pb-based layered cuprates with the 1222 structure have been synthesized in the (Pb0.5B0.5)Sr2 (RE2−xy Ce x Sr y )Cu2O z (RE = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Y) systems. The almost-single-phase samples in the systems can be obtained for a nominal composition of x=0.7 and y=0.1. The crystal structure of the samples has a tetragonal symmetry, the lattice parameters of a and c are increasing with increasing the ionic radius of RE element. Despite treatment under high O2 pressure of 100 atm, the samples are semiconductors with the transport process characteristic of three-dimensional variable range hopping conduction.  相似文献   

4.
New Pb-based layered cuprates containing boron with the 1232 structure have been synthesized in the (Pb0.5B0.5)Sr2(Er3−xy Ce x Sr y )Cu2O z system. Nearly the single 1232 phase samples are obtained for the nominal composition of 1.6≤x≤1.9 and y=0.2. A sample with the composition of (Pb0.5B0.5)Sr2(Er1.2Ce1.6Sr0.2)Cu2O z shows resistivity-dropping phenomenon below 10 K and it shows a diamagnetic signal at about 9.0 K, though the superconducting volume fraction is very small. From these results, the sample may well be a new Pb-based superconductor with the 1232 structure.  相似文献   

5.
We have synthesized new Pb-based 1222 cuprates containing sulfur in the (Pb0.75S0.25)Sr2(Eu2.0?x Ce x )Cu2O z system. X-ray diffraction study shows that almost the single 1222 phase samples can be obtained for a considerable wide area of 0.3≤x≤1.2 in the composition of (Pb0.75S0.25)Sr2(Eu2.0?x Ce x )Cu2O z . Next, the sample with x=0.4 after annealing under high-pressure O2 is discovered to show an onset of the resistivity drop at about 31 K and to show an onset of diamagnetic signal at about 29 K. These phenomena clearly indicate that the sample is a new superconductor.  相似文献   

6.
We previously reported on the synthesis of new Pb-based 1222 superconductor containing phosphorus in the (Pb0.75P0.25)Sr2(Eu1.9−x Ce x Sr0.1)Cu2O z system. Recently, we have discovered new members of the Pb-based 1222 superconductor containing phosphorus in the (Pb0.75P0.25)Sr2(Ln1.9−x Ce x Sr0.1)Cu2O z (Ln=Sm and Gd) systems. In each system, it is found that the samples of almost the single 1222 phase can be obtained for a wide composition area of 0.3≤x≤1.0. After annealing under 143 atm O2 atmosphere at 400 °C, each sample of Ln=Sm and Gd with x=0.3 is found to show an onset of resistivity-drop at about 28 K and at about 24 K, respectively. Moreover, each samples of Ln=Sm and Gd is found to show an onset of diamagnetic signal at about 25 K and about 22 K, respectively. From these facts, these samples of Ln=Sm and Gd are found to be new members of the Pb-based 1222 superconductor containing phosphorus.  相似文献   

7.
New Pb-based 1212 cuprates of (Pb0.8W0.2)Sr2(Nd1?x Ca x )Cu2O7?δ were synthesized. The sample with x=0.6 was reported to show superconductivity with an onset temperature up to 82 K. Interestingly, in order to obtain superconductivity of the sample, synthesis in N2 was necessary, then synthesis in air or post-treatment in O2 led to the disappearance of superconductivity. Recently, we have successfully synthesized new Pb-based 1222 cuprates for the composition range of 0.3≤x≤1.0 in the (Pb0.75W0.25)Sr2(Eu2.0?x Ce x )Cu2O z system. The samples have a tetragonal crystal structure; the typical lattice parameters are a=0.3850 nm and c=2.889 nm. Among them, a sample with x=0.3 is discovered to show superconductivity with an onset of about 15 K. These cuprates have the same (Pb, W)O monolayers as the Pb-based 1212 cuprates described above. In these new cuprates, superconductivity appears when the samples are annealed not in air and under He atmosphere, but under high-pressure O2.  相似文献   

8.
We have discovered new members of the Pb-based 1222 layered cuprates containing sulfur of (Pb0.75S0.25)Sr2(RE1.6Ce0.4)Cu2O z with RE = Sm, Gd, Dy, and Ho. All the samples are of almost-single 1222 phase. From the ρT and χT measurements, they are found to be superconductors after annealing under 125 atm O2 atmosphere at 400 °C. Among them, the sample with RE = Gd is found to show superconductivity at the highest temperature of 30 K.  相似文献   

9.
We already reported on the synthesis of new Pb-based 1212 layered cuprates containing sulfur in the (Pb0.75S0.25)Sr2(Y,Ca)Cu2O z system. There none of the samples showed superconductivity until after annealing under high O2 pressure. More recently, we have discovered that the samples could be substituted by Ba for Sr up to x=0.6 in the composition of (Pb0.75S0.25)(Sr2−x Ba x )(Y0.4Ca0.6) Cu2O z . Then if the Ba-substitution is performed for Sr, some of the almost-single phase samples are found to show resistivity drops and magnetic anomalies without annealing under high O2 pressure. Among the samples, a sample with the nominal composition of (Pb0.75S0.25)(Sr1.5Ba0.5)(Y0.4Ca0.6) Cu2O z is found to show the highest onset temperatures of a resistivity drop at about 35 K and a magnetic anomaly at about 31.5 K. These are higher than the highest values for the superconducting Ba-free sample of (Pb0.75S0.25)Sr2 (Y0.4Ca0.6)Cu2O z which was annealed under high O2 pressure.  相似文献   

10.
New Pb-based 1212 compounds containing phosphorus have been discovered in the (Pb1−y P y )Sr2(Y1−x Ca x )Cu2O z system; almost the single 1212 phase samples can be obtained for the composition range of 0.0≤x≤0.6 and y=0.25. The crystal structure for each sample has a tetragonal symmetry with the typical lattice parameters a=0.3828 nm and c=1.182 nm. Among them, the sample with x=0.6 and y=0.25 shows the onset of resistivity drop at about 39 K and zero-resistivity at about 17 K. Moreover, the sample shows a diamagnetic signal at about 38 K. These phenomena are found to originate from superconductivity with the bulk feature.  相似文献   

11.
(Tl1?x Pb x )(Sr2?y Ba y )Ca3Cu4O z samples were synthesized by using a two-step solid state reaction method and examined with respect to the (Tl,Pb)-1234 phase formation and superconducting properties. Samples were prepared from various starting compositions of 0≤x≤0.5 and 0.4≤y≤2.0. Nearly single-phased samples were obtained for (Tl0.8Pb0.2)(Sr2?y Ba y )Ca3Cu4O z (1.0≤y≤1.25) and (Tl1?x Pb x )(SrBa)Ca3Cu4O z (0.15≤y≤0.35). We have found that both the partial substitution of Ba for Sr and the partial substitution of Pb for Tl are effective for the formation of the Tl-1234 phase. Bulk superconductivity with a T c value of 106 K is observed in the (Tl0.7Pb0.3)(SrBa)Ca3Cu4O z sample.  相似文献   

12.
Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi2−y Pb y )Sr2(Sr1−x Ce x )Cu2O z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition ofx=0.23 andy=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.  相似文献   

13.
The structural and superconducting properties of (Er1-xCax)Ba2-ySry(Cu2.76Co0.24)Oz are investigated using X-ray diffraction, resistivity, ac susceptibility, and oxygen content measurements. Increasing the Sr content in (Er0.76Ca0.24)Ba2-ySry(Cu2.76Co0.24)Oz lowers the oxygen content and decreases theT c, which is attributed to the rearrangement of oxygen atoms in the basal plane. This suppression ofT c aty =0.6 cannot be improved by appropriate hole doping with Ca in (Er1-xCax)Ba1.4Sr0.6(Cu2.76Co0.24)Oz forx = 0.24-0.48.  相似文献   

14.
Synthesis of the Bi-2212 compound in the Bi-Sr-Ce-Cu-O system has been already known. But, there has been no report on superconductivity of the compound yet. We have prepared many Bi-2212 samples partially substituted by Pb for Bi in the Bi-Sr-Ce-Cu-O system. The nominal composition is (Bi2− y Pb y )Sr2(Sr1− x Ce x )Cu2O z . Then, we have investigated possibility of superconductivity for the samples. As a result, we find that a sample with nominal composition of x=0.23 and y=0.1, which is of almost the single 2212 phase, shows an anomaly at about 70 K in addition to temperature dependence of the resistivity like a semiconductor. Furthermore, the sample also shows a decrease of magnetic susceptibility starting at about 70 K with decreasing temperature. These experimental results can be considered to result from superconductivity of the 2212 phase in the Bi(Pb)-Sr-Ce-Cu-O system.  相似文献   

15.
The single-phased series of Sr-bearing Hg-1212 superconducting cuprate,(Hg0.7Mo0.3)Sr2(Sr1?x La x )Cu2O z has been prepared. X-ray diffraction showed that, the obtained samples belong to the 1212-structure with tetragonal space group P4/mmm, similar to that of (Hg, Mo)Sr2(Ca, Y)Cu2Oz, and stabilized in a wide compositional range of 0.25≤x≤0.75. Refinements of the structure are carried out in which the oxygen atoms at the (Hg, Mo) layer is shifted from high-symmetry position (0.5, 0.5, 0) to (x, x, 0). Magnetization and electrical resistivity measurements show that the as-prepared samples exhibit evidence for superconductivity and their superconducting properties were improved after O2 annealing with T onset c as high as 92 K.  相似文献   

16.
Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi2Sr2- (Ln1−x Ce x )2Cu2O10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln1−x Ce x )2O2 block between two CuO5 pyramids in the crystal structure. The tetravalent ions of Ce4+ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi2Sr2(Ln2−x Zr x )Cu2O z (Ln = Sm, Eu, Gd, and Dy) systems, where Zr4+ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce4+. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi2Sr2(Gd2−x Zr x )Cu2O z system are also reported.  相似文献   

17.
New Pb-based 1222 cuprates containing phosphorus have been synthesized in the (Pb,P)Sr2(Eu,Ce,Sr)2 Cu2O z system. From X-ray powder diffraction study, almost the single 1222 phase samples are found to be obtained in a considerable wide composition area of 0.3≤x≤1.2 for the nominal composition of (Pb0.75P0.25)Sr2(Eu1.9−x Ce x Sr0.1) Cu2O z . The crystal structure for each sample has a tetragonal symmetry and the typical lattice parameters are a=0.3851 nm and c=2.922 nm. After annealing under 143 atm O2 atmosphere at 400 °C, a sample with x=0.3 among the almost-single phase samples shows an onset of resistivity-drop at the highest temperature of about 22 K and zero-resistivity at the highest temperature of about 12 K, then this sample also shows an onset of diamagnetic signal at about 20 K. These phenomena are found to originate from superconductivity of the new 1222 phase.  相似文献   

18.
In this paper, the effect of Sb and Pb elements doping on the Bi1.6Pb x Sb y Sr2Ca2Cu3O z (BPSSCCO) superconductor was studied. The BPSSCCO superconductor was synthesized by a solid state reaction method. The superconductivity properties such as the critical temperature, magnetic susceptibility, and room temperature resistivity have been investigated. In order to study the effect of Sb and Pb elements on the room temperature resistivity of the samples, the V–I curves were measured. The resistivity of the Sb doped samples at room temperature increases when the content of Sb is increased. It is also decreased by increasing the annealing time. The results showed that the optimum condition was x=0.35, y=0.05, with an annealing time of 270 h.  相似文献   

19.
We have investigated effects of the lanthanide element Ln and the composition changes on the superconducting transition temperatureT c in the Ru-1232 system, RuSr2(Gd1−x Ln x Ce1.8Sr0.2)Cu2O z (Ln = Sm, Dy, and Ho). At first, in the case of the samples with Ln = Sm among almost the single 1232 phase samples, the values of the superconducting onset temperatureT co are almost the same forx=0.00−0.15, and each of the lattice parametersa andc is almost constant. While, in each of the cases of the samples with Ln = Dy and Ho, the sample withx=0.05 shows the maximum values for both the superconducting onset temperatureT co and the zero resistivity temperatureT cz. Especially for the sample with Ln = Dy, the values ofT co andT cz are 18.5 and 6.5 K, respectively. These are higher than those of the mother sample of RuSr2(GdCe1.8Sr0.2)Cu2O z . Moreover, from variations ofT co, lattice parameters ofa andc in the RuSr2(Gd1−x Dy x Ce1.8Sr0.2)Cu2O z system as a function of Dy contentx, the relationship between the superconducting transition temperature and the lattice parameters in the present system are investigated.  相似文献   

20.
New cuprates with nominal composition (Pb0.8W0.2)Sr2(Nd1 ? x Ca x )Cu2O7 ? δ(0≤x≤1) were synthesized by solid-state reaction in N2. The crystal structure was characterized by X-ray powder diffraction (XRD) as tetragonal. Direct current electrical resistance measurements were applied to check the existence of superconductivity in these cuprates. Superconductivity with T c (onset) up to 82 K is observed when x = 0.6. Synthesis in N2 is necessary in obtaining superconductivity in these cuprates. Preparation in air or post-treatment in flowing oxygen destroys superconductivity. A comparison is made with previous Pb-based 1212 superconducting oxides. The valence of Pb and the possible position of W in the lattice are discussed.  相似文献   

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