Search

Branched CuInSe 2 nanowires (NWs) are successfully synthesized by one-pot method for making secondary bismuth nanoparticles to attach onto the CuInSe 2 NWs stem for inducing the secondary branch growth by solution-liquid-solid (SLS). The branched CuInSe 2 NWs were measured in order to reveal its viability for PV device fabrication and application for the light-absorbing material in solar cells.

Based on first principles with the Tran-Blaha modified Becke-Johnson potential, pure and doped Ba5Nb4O15 have been investigated as highly efficient photocatalysts for solar water splitting. The results showed that the calculated band gap of Ba5Nb4O15 is improved to 3.81 eV by the new potential. Mono-doping with either anion (N, P) or cation (Mo) creates some partially occupied states at the band edges of Ba5Nb4O15. N–Mo co-doping and P–Mo co-doping can prevent the partially filled states from appearing at band edges and hence enhance the photocatalytic efficiency. The band edges of the co-doped systems still satisfy the requirements for spontaneous water splitting. More importantly, the band gap of P–Mo co-doped system is sharply reduced to 2.31 eV, being in ideal visible light region. The defect formation energy calculations show that P–Mo co-doped Ba5Nb4O15 is energetically favorable under O-rich and Nb-poor conditions. These show that P–Mo co-doped Ba5Nb4O15 has high efficiency for water splitting under visible light.

The effects of mono-doping (N, C, La, and Ce) and co-doping (N–La, C–Ce, and N–Ce–N) on the electronic structure of SrTiO3 are studied by the first-principles method. The results show that some partially occupied states acting as recombination centers appear in the mono-doped systems and thereby suppress their photocatalytic activity. The co-doping can inhibit the partially occupied states and thus keep the high activity of photocatalysis. Further, the (N–Ce–N) co-doping can significantly narrow the band gap of SrTiO3 to make it fall in the visible light region while keeping the match of the band edges with the redox potential for water splitting. The high activity and narrowed band gap show that the (N–Ce–N) co-doped SrTiO3 is a good candidate for water splitting under visible light irradiation.

Fe-clad BaxK1-xFe2As2 superconducting tapes were fabricated by the ex situ powder-in-tube method combined with a short high-temperature annealing technique. The effect of annealing time and different dopants on the transport properties of the BaxK1-xFe2As2 tapes were systematically studied. By co-doping with Ag and Pb, the transport critical current density Jc of BaxK1-xFe2As2 tapes was significantly improved in whole field region and the highest transport Jc was up to 1.4x10^4 A/cm^2 (Ic=100 A) at 4.2K in self field. It is proposed that the superior Jc in the co-doped samples are due to the combine effect of Pb doping at low fields and Ag doping at high fields., Comment: 22 pages, 7 figures, to be published in Supercond. Sci. Technol

SmFeAsO1-xFx tapes were prepared using three kinds of starting materials. It shows that the starting materials have an obvious effect on the impurity phases in final superconducting tapes. Compared with the other samples, the samples fabricated by SmAs, FeO, Fe2As, and SmF3 have the smallest arsenide impurity phase and voids. As a result, these samples possess much denser structure and better grain connectivity. Moreover, among the three kinds of samples fabricated in this work, this kind of sample has the highest zero-resistivity temperature ~40 K and largest critical current density ~4600 A/cm^2 in self-field at 4.2 K. This is the highest Jc values reported so far for SmFeAsO1-xFx wires and tapes., Comment: 15 pages, 4 figures

MgB2 multifilamentary wires and tapes were fabricated by the in situ powder-in-tube (PIT) process using acetone doped milled precursor powders. The critical current density of MgB2 is strongly enhanced by high energy milling and acetone doping. Furthermore, the liquid acetone can restrain the agglomeration of milled powder, which is beneficial to the fabrication of MgB2 multifilamentary wires. At 4.2 K and 10 T, the Jc of the 80 h doped Fe/Cu wire is 2.9 × 103 A cm−2, 20 times larger than that of the 1 h pure one (the '1 h' and '80 h', refer to ball milling times). The Jc of 80 h doped Fe/Monel tape is up to 9.2 × 103 A cm−2 at 4.2 K and 10 T. The Jc values of Nb barrier wires are comparable to those of the Fe barrier MgB2 wires. These results indicate that the addition of liquid C-containing material during high energy milling may be an effective way to get excellent properties of MgB2 for practical applications.

A comparative study of the addition of Pb to polycrystalline Ba0.6K0.4Fe2As2 has revealed that the Pb should be added after the Ba0.6K0.4Fe2As2 phase has formed. The uniformly dispersed Pb can ameliorate the Ba0.6K0.4Fe2As2 grain linkages. In contrast, pre-added Pb in the raw powder congregates to form large particles and has hardly any positive effect on the Jc enhancement. To conglutinate at the grain surface and avoid contamination of the Ba0.6K0.4Fe2As2, the material added should have a low melting point and inertia to the superconducting phase. This model also enables us to predict desirable dopants for enhancing superconducting properties of Ba0.6K0.4Fe2As2.

C-doped MgB2 tapes were fabricated using crystalline boron as one of the ball milled precursor powders. It was found that the ball milling process can strongly enhance the Jc values of MgB2 tapes and reduce the anisotropy of the Jc. At 4.2 K, the transport Jc of the 80 h milled C-doped MgB2 tapes sintered at 800 °C reaches 4.3 × 104 A cm−2 at 10 T and 2.2 × 104 A cm−2 at 12 T, respectively. These values are even higher than for tapes made from amorphous B powders. Ball milling can improve not only the upper critical field, by increasing the C substitution level in the MgB2 lattice, but also the flux pinning, by increasing grain boundaries, both of which result in the enhancement of Jc performance. Moreover, the high MgB2 phase fraction and large density of milled MgB2 tapes are beneficial to the active area. These results indicate that the use of crystalline B in combination with a ball milling process may be an economic method to harness the excellent properties of MgB2 for practical applications.

The effect of the hot pressing method on in situ powder-in-tube-processed MgB2/Fe tapes was studied. The tapes doped with and without nanosized C are hot-pressed at 100?MPa and 650?800??C for 1?5?h in a flowing Ar gas atmosphere. Compared to the non-hot-pressed tapes, the Jc?B property (at 4.2?K and 10?T) of pure and C-doped samples hot-pressed at 650??C for 5?h was enhanced by a factor of 2.5 and 1.4, respectively. For hot-pressed tapes, the optimized sintering temperature is below 700??C at 100?MPa. The enhancement of Jc performance for hot-pressed MgB2 samples is mainly attributed to the improved grain connectivity.

MgB2 bulks and tapes were fabricated using ball-milled precursor powders. The selected B powders have the ?-rhombohedral crystalline structure as a main phase, with a small amount of MgO impurity. Milling time was tested from 0.5 to 120?h to get an optimized value. It is found that ball milling can facilitate MgB2 phase formation, refine the MgB2 grains and increase the defect density. Moreover, the active area, Bc2 and flux pinning are improved, which is of benefit to the enhancement of Jc performance. The 80 h milled MgB2 bulk sample has a Jc value of 2.8???104?A?cm?2 at 5?K and 6?T, 41 times larger than that of the 0.5?h sample. At the same time, the transport Jc of the 80?h MgB2 tape reaches 2.3???103?A?cm?2 at 4.2?K and 9?T, 32 times larger than that of the 0.5?h one. Due to the increase of impurities and the release of lattice deformation and strain, the Jc was decreased for the sample milled up to 120?h.

Polycrystalline Ba0.6K0.44Fe2As2.2 was fabricated using a two-step solid reaction method by two different sintering processes. Although different microstructures were observed between these samples, similar superconducting properties were obtained. It seems that the sequence for high temperature with short annealing time and low temperature with long sintering time has little effect on the superconducting properties of the Ba0.6K0.44Fe2As2.2 sample. But, for the Ag-added samples, the Jc value was significantly affected by the sintering process, indicating a different mechanism to pure Ba0.6K0.44Fe2As2.2.

MgB2 tapes were fabricated by the in situ powder-in-tube method using C2H4O3-treated B powder as a source material. It is found that the Jc values of MgB2 tapes are significantly improved by treating B powder with C2H4O3. At 4.2 K, the Jc of the C2H4O3-treated sample sintered at 800 °C reaches 5 × 103 A cm − 2 at 12 T. The C2H4O3-treated B improves not only the upper critical field through enhancing intraband scattering but also the flux pinning by increasing grain boundaries and C substitution effects. A larger amount of intragranular structural defects and grain boundaries were found in the C2H4O3-treated MgB2 matrix. Benefiting from the good crystallinity, the C2H4O3-treated tape sintered at 800 °C shows a bigger active area fraction and a higher Jc than the sample sintered at 700 °C. These results suggest that treating B powder with C2H4O3 is an effective way to enhance the critical current density of MgB2 superconductors.

We report the effect of yttrium acetate addition on in situ powder-in-tube processed MgB2/Fe tapes. The amount of yttrium acetate was varied from 0 to 20?wt% and sintering was performed at 700?850??C for 1?h in a flowing Ar atmosphere. We found that a significant Jc?B enhancement was easily achieved in high field by yttrium acetate doping. At 4.2?K, the transport Jc for the best yttrium-acetate-added tapes (10?wt%) reached almost 104?A?cm ? 2 at 12?T. The improvement of Jc performance in the yttrium-acetate-doped samples can be attributed to the combination of the carbon substitution for B and stronger flux pinning.