Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics

Lithium can be inserted reversibly within most carbonaceous materials. The physical mechanism for this insertion depends on the carbon type. Lithium intercalates in layered carbons such as graphite, and it adsorbs on the surfaces of single carbon layers in nongraphitizable hard carbons. Lithium also appears to reversibly bind near hydrogen atoms in carbonaceous materials containing substantial hydrogen, which are made by heating organic precursors to temperatures near 700°C. Each of these three classes of materials appears suitable for use in advanced lithium batteries.

Mechanisms for Lithium Insertion in Carbonaceous Materials

Single-crystalline iron oxide nanotubes.

We examine the effect on the superconducting transition temperature ${(T}_{\mathrm{c}})$ of chemical inhomogeneities in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals. Cation disorder at the Sr crystallographic site is inherent in these materials and strongly affects the value of ${T}_{\mathrm{c}}.$ Partial substitution of Sr by Ln (Ln = La, Pr, Nd, Sm, Eu, Gd, and Bi) in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{1.6}{\mathrm{Ln}}_{0.4}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ results in a monotonic decrease of ${T}_{\mathrm{c}}$ with increasing ionic radius mismatch. By minimizing Sr site disorder at the expense of Ca site disorder, we demonstrate that the ${T}_{\mathrm{c}}$ of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ can be increased to 96 K. Based on these results we discuss the effects of chemical inhomogeneity in other bulk high-temperature superconductors.

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Effect of chemical inhomogeneity in bismuth-based copper oxide superconductors

Silver-sheathed BiPbSrCaCuO wires were fabricated using the powder-in-tube method. Critical current densities at 77.3 K were 4.7*10/sup 4/ A/cm/sup 2/ in a zero magnetic field, 3.1*10/sup 4/ A/cm at 0.1 T, and 1.1*10/sup 4/ A/cm/sup 2/ at 1 T. In liquid He, these wires can carry 1.03*10/sup 5/ A/cm/sup 2/ at 23 T. J/sub c/ and J/sub c/-B enhancements are due to grain-boundary improvements. Detailed investigation of J/sub c/-B characteristics in magnetic fields, especially increasing and decreasing fields, revealed that history effect behaviours caused by weak links disappeared with improvements of grain-boundary characteristics at both temperatures. It was observed that 1296 multifilamentary wires were capable of sustaining over 70% of J/sub co/ even after a strain of up to 0.66% repeated 10 times. Prototypes of coils and current leads were fabricated using 20-m-long wires. One coil showed critical currents of 54.2 A at 77.3 K and 367 A at 4.2 K. This coil generated a B/sub m/ of 142 G at 77.3 K and 876 G at 4.2 K. A prototype of a react & wind-processed coil was demonstrated using greater than 4-m-long multifilamentary wires, and it successfully produced enough magnetic field to rotate copper windings between steel cores.

High-J/sub c/ silver-sheathed Bi-based superconducting wires

Partial substitution of Pb for Bi in the Bi-Sr-Ca-Cu-O system has been found to sharply increase the volume fraction of the high-Tc phase when both the starting material (coprecipitated oxalate being used in the present study) and the heating process are appropriate. The sharp powder X-ray diffraction pattern obtained from well-grown particles, 5~10 µm wide and 0.5 µm thick typically, was assigned to an orthorhombic cell with a=0.537 nm, b=2.682 nm, and c=3.726 nm. The electrical resistance dropped to zero at 107 K within the experimental limit of 10-6 Ω. A large diamagnetic response in the ac susceptibility due to the Meissner effect was seen below 120 K. The dominance of the high-Tc phase over the low-Tc phase was roughly estimated at 9/1 in volume.

https://iopscience.iop.org/article/10.1143/JJAP.27.L1041/pdf

High-Tcphase promoted and stabilized in the Bi, Pb-Sr-Ca-Cu-O system

Solid phases and their relations in the Bi-Sr-Cu-O system were investigated at 840°C in air. Bi 2+ x Sr 2− x Cu 1+ y O Z (0.1 x y x /2), Bi 17 Sr 16 Cu 7 O Z , Bi 2 Sr 3 Cu 2 O Z , Bi 4 Sr 8 Cu 5 O Z and BiSr 3 O Z have newly been found. Structural data obtained by means of powder XRD and TEM for these are presented. The superconductor with a T c ∼ 10 K corresponds to the Bi-poorest end of the solid solutions mentioned above. Carrier holes are created by the presence of excess oxygen but these tend to be trapped locally for x > 0.13. The one-dimensional modulation mode showed an interesting composition dependence, from which a modified mechanisms of the modulation has been deduced.

Phases and their relations in the Bi-Sr-Cu-O system

Magnetic properties of La-Co substituted M-type strontium hexaferrites prepared by polymerizable complex method

β-Fe2O3 is the scarce polymorph of Fe2O3 phases and is transformed easily into α-Fe2O3 at high temperature. However, its crystal structure and the transformation mechanism to α-Fe2O3 are still uncl...

Crystal Structure of β-Fe2O3 and Topotactic Phase Transformation to α-Fe2O3

The superconducting transition of YBa2Cu3O6.86 has been studied in terms of complex susceptibility. It is found that the transition has two phases. One is insensitive to the change in the amplitude, h0 (5-1000 mOe), of the external ac field. The other is very sensitive to h0, where the transition width is appreciably broadened as h0 increases. No frequency dependence is found below 320 Hz. These behaviors are qualitatively common to the other oxide superconductors, La1.9Sr0.1CuO4-x and ErBa2Cu3O6+x. Discussion is made in the framework of the phenomenological weak-link loop model.

Yasunori Ikeda

Papers

High-Tcphase promoted and stabilized in the Bi, Pb-Sr-Ca-Cu-O system

Phases and their relations in the Bi-Sr-Cu-O system

Magnetic properties of La-Co substituted M-type strontium hexaferrites prepared by polymerizable complex method

Crystal Structure of β-Fe2O3 and Topotactic Phase Transformation to α-Fe2O3

Complex susceptibility of YBa2Cu3O6.86