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1.
We report synthesis and superconductivity at 3.7 K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having a ZrCuSiAs-type structure. The bulk polycrystalline compound is synthesized by the vacuum encapsulation technique at 780 °C in a single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in a tetragonal P4/nmm space group with lattice parameters a=4.015(5) Å, c=13.362(4) Å. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4 K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (T c ) onset at 3.7 K and T c (ρ=0) at 3.1 K. The hump at T c related to the superconducting transition is not observed in the heat capacity measurement and rather a Schottky-type anomaly is observed at below ~6 K. The compound is slightly semiconducting in a normal state. Isothermal magnetization (MH) exhibited typical type II behavior with a lower critical field (H c1) of around 8 Oe.  相似文献   

2.
The effect of Cd doping on structure and superconductivity in Mg0.5Cd0.5B2 fabricated by a solid-state reaction at ambient pressure has been investigated. The resulting changes in crystal structure, superconducting transition temperature T c and critical current density J c are characterized by X-ray diffraction, dc magnetization, electrical resistance, and magnetic measurements. It reveals that Cd does not occupy the atomic Mg sites in the MgB2 crystal structure, but merely reacts with Mg and forms a MgCd3 phase. It is striking to note that although the nonsuperconducting phase MgCd3 is as high as about 67 vol.% in Mg0.5Cd0.5B2, the T c of the doped sample drops only by about 1 K. Most important, a surprising improvement of J c of 5.0 × 105 A/cm2 (5 K, 0 T) has been achieved in Mg0.5Cd0.5B2. It is suggested that the improvement in J c in Mg0.5Cd0.5B2 is primarily due to pinning effects induced by MgCd3. Also, it is thought that MgCd3 may fill up gaps among grains in MgB2 and produce better grain linkage, which may be another source of improvement in J c in Mg0.5Cd0.5B2.  相似文献   

3.
In the present short letter, we report on the low dimensional 4d and 5d transition metals-chalcogenide based compounds i.e., Ta2PdxS6, showing semiconducting to superconducting transition at around 4K with their upper critical fields outside the Pauli paramagnetic limit. It seems couple of different superconducting phases do exist in these new set of compounds. Our short letter in this regards is thought provoking, asking to explore various unearthed possible new superconducting phases in (Nb/Ta)2Pdx(S/Se/Te)y systems.  相似文献   

4.
The Coulomb interaction induces low-energy electronic collective modes (LEECM) in layered conductors. We study how the superconducting critical temperature T c is affected by such collective modes within the strong-coupling theory of superconductivity. Whereas we account for both the electron–phonon and the screened Coulomb interactions, the main focus is set on the latter. The dielectric function is displayed and screening within RPA is discussed. We then show that LEECM affect the superconducting state constructively in layered structures. Their effect can be interpreted as a negative * in the Eliashberg theory. We examine in what respect the collective-mode scenario differs in layered conductors as compared to three-dimensional (3D) isotropic metals.  相似文献   

5.
Metallochloronitrides are layered conductors that have recently been found to superconduct at critical temperatures up to T c 26 K. It is known that the electron–phonon interaction is small in these systems, so that the conventional pairing mechanism through exchange of phonons is unable to provide for such high T cs. We show that the dominant contribution to the pairing interaction in these materials comes from the exchange of low-energy collective modes, specific to layered conductors. The existence of such acoustic plasmons results from the incomplete screening of the Coulomb interaction perpendicular to the conducting planes which expresses itself in the dynamical nature of the screened Coulomb interaction.  相似文献   

6.
AC magnetic susceptibility, (T), and do resistivity, (T), measurements have been performed to study the superconductivity and magnetic properties of a polycrystalline Eu1.5Ce0.5RuSr2Cu2O10. X-ray diffraction shows that the single-phase compound crystallized into a tetragonal symmetry of space group I4/mmm. Ru spin ordering and superconductivity at 75 and 37 K, respectively, were evident in (T). The magnetic responses associated with the Ru spin ordering were found to be strongly reduced by a weak applied field, indicating an antiferromagnetic character for the Ru moments. A two-step transition to the superconducting state was observed in (T), where an intra-granular transition at T C1=37 K and an inter-granular transition at T C2=20 K were clearly seen. These observations confirm the coexistence of superconductivity and magnetic order at low temperatures.  相似文献   

7.
以Li2CO3,Ni(OH)2,MnCO3,TiO2为原料,采用高温固相合成法制备了层状Li(Ni0.5Mn0.5)1-xTixO2.通过X射线衍射确定了不同钛掺杂量样品的相组成.用扫描电镜对组织形貌进行了观测.对用所制样品组装的电池的充放电和循环性能进行了测试.实验结果得出:所制备的Li(Ni0.5Mn0.5)1-xTixO2的结构为α-NaFeO2型层状结构,当x=0.02时,Li(Ni0.5Mn0.5)1-xTixO2的首次放电容量为161 mA·h/g,25次循环后容量仍保持在144 mA·h/g,具有较高的比容量和良好的循环性.  相似文献   

8.
We address the question whether or not acoustic collective modes contribute to superconductivity in a layered electron gas. We calculate T c within the strong-coupling phonon-plasmon scheme. The plasmon pairing kernel is calculated explicitly. We demonstrate that plasmons may contribute constructively to superconductivity. The result shows that one can interpret the effect of low-energy collective modes in terms of an effective negative *.  相似文献   

9.
10.
This work reports a systematic study on the structural and superconducting properties in the Hg-Sm-In-Pb system. It is investigated how In and Sm dopings influence the superconducting properties of the HgPb2 phase which was recently reported. Results for the HgSm1 − xPb2 system show that Sm atoms substitute Hg vacancies in the tetragonal phase which do not affect the onset critical temperature of the HgPb2 compound. Simultaneous Sm and In doping effects on the properties of the HgPb2 phase are also studied. Experimental and simulations of X-ray powder diffractograms suggest that the HgSm1 − xInxPb2 system (0.2 ≤ x ≤ 0.7) has a pseudo-cubic structure with lattice parameters near 4.88 Å. Superconducting properties measurements show that this system has an optimum doping at x ∼ 0.5 with the onset critical temperature close to 6.9 K. This is the highest superconducting critical temperature for the AuCu prototype so far reported.  相似文献   

11.
The effect of Cd doping on structure and superconductivity in Mg0.5Cd0.5B2 fabricated by a solid-state reaction at ambient pressure has been investigated. The resulting changes in crystal structure, superconducting transition temperature T c and critical current density J c are characterized by X-ray diffraction, dc magnetization, electrical resistance, and magnetic measurements. It reveals that Cd does not occupy the atomic Mg sites in the MgB2 crystal structure, but merely reacts with Mg and forms a MgCd3 phase. It is striking to note that although the nonsuperconducting phase MgCd3 is as high as about 67 vol.% in Mg0.5Cd0.5B2, the T c of the doped sample drops only by about 1 K. Most important, a surprising improvement of J c of 5.0 × 105 A/cm2 (5 K, 0 T) has been achieved in Mg0.5Cd0.5B2. It is suggested that the improvement in J c in Mg0.5Cd0.5B2 is primarily due to pinning effects induced by MgCd3. Also, it is thought that MgCd3 may fill up gaps among grains in MgB2 and produce better grain linkage, which may be another source of improvement in J c in Mg0.5Cd0.5B2.  相似文献   

12.
A bulk polycrystalline sample with the nominal compositions represented by V2AlN1?δ was synthesized by a two-step solid-state reaction. The structural characterization has been done via X-ray diffraction, followed by Rietveld refinements, which revealed that the layered V2AlN is crystalized in cubic Fm3m space group with lattice parameters a = b = c = 6.127 Å. Both DC resistivity and magnetization measurements confirmed that V2AlN is a bulk superconductor with superconducting transition temperature (T c ) of 15.9 K.  相似文献   

13.
Semiconducting TMDs are nowadays attracting great interest after the invention of the so-called “Scotch-tape method” established in graphene research. Semiconducting TMDs are front-runners of “post graphene” materials for their finite band gap crucial for device applications. MoS2 is the most widely used TMD because of its application as a solid lubricant. Scientifically, it shows superconductivity after alkali or alkaline-earth doping with a highest T c of around 7 K. Recently, we succeeded in inducing superconductivity in the MoS2 transistor adopting electric double layer (EDL), a nanosized capacitor, as a gate dielectric. The field-induced superconducting transition of MoS2 was realized with a maximum T c around 11 K, the highest not only within a reported MoS2 compound, but also among TMDs. This highest T c lies in the carrier density region much smaller than a chemically doped compound; a low density region has never been successfully accessed by chemical methods. Combining a HfO2 (high-k) back gate, quasi-continuous control of carrier density, and thus quantum phase, was demonstrated to unveil the phase diagram; the T c exhibits strong carrier density dependence with a superconducting dome. Our result implies a common existence of the superconducting dome in 2D band insulators.  相似文献   

14.
晶态骨架介孔CeO2和CeO2-ZrO2的合成与结构表征   总被引:1,自引:0,他引:1  
以乙酸铈、乙酸锆为无机源,嵌段共聚物P123为模版剂,采用溶胶-凝胶法合成了介孔CeO2及CeO2-ZrO2复合体,用XRD、氮气吸附脱附、TEM、HRTEM、SAED等对材料进行了表征.结果表明,所得介孔CeO2具有规则的晶态孔道结构,孔径约在10nm左右,特别是其孔壁晶粒高度定向排列且平行于孔道方向.原位高温TEM观测表明,该介孔CeO2在800℃仍具有很高的孔道完整性.掺杂ZrO2后发现,在ZrO2摩尔含量低于30%时仍具备高度定向排列结构,高于30%时骨架晶粒取向逐渐趋向无序化.  相似文献   

15.
Starting from a two-orbital model and based on the random phase approximation, spin excitations in the superconducting state of the newly discovered BiS2 superconductors with three possible pairing symmetries are studied theoretically. It is found that the spin response is uniquely determined by the pairing symmetry. Possible spin resonance excitations may occur at an incommensurate momentum about (0.7π,0.7π) for the d-wave symmetry, while the transverse spin excitation near (0,0) is enhanced for the p-wave symmetry and no spin resonance signature is seen for the s-wave pairing symmetry. These distinct features may be used for probing or determining the pairing symmetry in this newly discovered compound.  相似文献   

16.
Ion storage CeO2 and CeO2/SnO2 coatings were prepared by the sol-gel dip-coating method using an aqueous-based process. The influence of added SnO2 in the CeO2 oxide coatings on the inserted/extracted charge was determined by chronocoulometric measurements. It was found that for 60 nm thick film, the inserted/extracted charge was twice (Q=10 mC cm–2) as large for films containing 17 mol% SnO2, if compared to pure CeO2. The effect of the addition of SnO2 to the mixed oxide coatings on their optical properties and structural characteristics was studied.  相似文献   

17.
18.
A strontium tantalum sulfide, SrTa2S5, has a hexagonal structure with lattice constants of a =3.32 and c=24.1 Å. With decreasing temperature the electrical resistivity decreases monotonically and exhibits an abrupt superconducting transition at 3.16 K (midpoint). The diamagnetic susceptibility is observed below Tc. The magnetic susceptibility is nearly independent of temperature above Tc and shows Pauli paramagnetism.  相似文献   

19.
20.
The layered perovskite oxide Sm1.5SrBa0.5Mn2O7 was synthesized by the conventional method of co-precipitation. Its structure has been solved by powder X-ray diffraction. The diffraction patterns are consistent with the I4/mmm symmetry, with tetragonal lattice parameters a=3.8398(7) Å and c=20.3814(5) Å. The structure of Sm1.5SrBa0.5Mn2O7 is similar to Sr3Ti2O7. Magnetic measurements were also performed in the temperature range 2–360 K. They showed a strong presence of antiferromagnetic interactions below Neel temperature T N=25 K. The variation of the magnetization with the magnetic field in a temperature of 5 K was also analyzed. No saturation was observed up to the high applied magnetic field of 10 T.  相似文献   

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