There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

Materials science challenges for high-temperature superconducting wire

Polymers containing fullerene or carbon nanotube structures

Solid-state lighting has made tremendous progress this past decade, with the potential to make much more progress over the coming decade. In this article, the current status of solid-state lighting relative to its ultimate potential to be “smart” and ultra-efficient is reviewed. Smart, ultra-efficient solid-state lighting would enable both very high “effective” efficiencies and potentially large increases in human performance. To achieve ultra-efficiency, phosphors must give way to multi-color semiconductor electroluminescence: some of the technological challenges associated with such electroluminescence at the semiconductor level are reviewed. To achieve smartness, additional characteristics such as control of light flux and spectra in time and space will be important: some of the technological challenges associated with achieving these characteristics at the lamp level are also reviewed. It is important to emphasise that smart and ultra-efficient are not either/or, and few compromises need to be made between them. The ultimate route to ultra-efficiency brings with it the potential for smartness, the ultimate route to smartness brings with it the potential for ultra-efficiency, and the long-term ultimate route to both might well be color-mixed RYGB lasers.

Toward Smart and Ultra-Efficient Solid-State Lighting

Perovskite-Type Oxides: I. Structural, Magnetic, and Morphological Properties of LaMn1−xCuxO3 and LaCo1−xCuxO3 Solid Solutions with Large Surface Area

{ital T}{sub {ital c}} and {ital dT}{sub {ital c}}/{ital dP} have been systematically measured for fully oxygenated {ital R}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} ({ital R}-123) with {ital R}=Yb, Tm, Ho, Dy, Gd, Sm, and Nd. {ital T}{sub {ital c}} has been observed to increase from 88 to 94 K with increasing radius of the {ital R} ion ({ital r}) from 0.98 to 1.12 A. Based on the lattice strains and our {ital dT}{sub {ital c}}/{ital dP} data, we have calculated {ital T}{sub {ital c}} for the series of {ital R}-123 and compared them with the measured {ital T}{sub {ital c}}. Good agreement between the experimental and the calculated results strongly suggests that the {ital R} effect on {ital T}{sub {ital c}} in {ital R}-123 originates from the strain-induced charge redistribution between the charge reservoir and the CuO{sub 2} plane.

Origin of the R-ion effect on Tc in RBa2Cu3O7.

Synthesis of novel conducting elastomers as polyaniline-interpenetrated networks of fullerenol-polyurethanes

Determination of Mn Valence from X-Ray Absorption Near Edge Structure and Study of Magnetic Behavior in Hole-Doped (Nd1−xCax)MnO3System☆

O K-edge and Cu L{sub 23}-edge x-ray-absorption near-edge structure (XANES) spectra for the series of (Dy{sub 1{minus}x}Pr{sub x})Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} compounds (x=0{endash}0.7) were measured to investigate how the variation of hole states related to the superconductivity. Near the O 1s edge, prepeaks at {approximately}527.6 and {approximately}528.4 eV are assigned to transitions into O 2p holes located in the CuO{sub 3} ribbons and CuO{sub 2} planes, respectively. Both the O 2p hole concentration in the CuO{sub 2} planes and CuO{sub 3} ribbons decrease monotonically with increasing Pr doping, giving evidence in support of the hole depletion model proposed by Liechtenstein and Mazin. It clearly demonstrates that the suppression of superconductivity with Pr-doping results predominantly from the hole depletion effect. In the Cu 2p absorption edge, the high-energy shoulders originating from Cu3d{sup 9}L defected states show a linear decrease in spectral weight as the Pr doping increases, where L denotes the ligand O 2p hole on the CuO{sub 3} ribbons and the CuO{sub 2} planes. {copyright} {ital 1997} {ital The American Physical Society}

C. Y. Huang

Papers

Origin of the R-ion effect on Tc in RBa2Cu3O7.

Synthesis of novel conducting elastomers as polyaniline-interpenetrated networks of fullerenol-polyurethanes

Determination of Mn Valence from X-Ray Absorption Near Edge Structure and Study of Magnetic Behavior in Hole-Doped (Nd1−xCax)MnO3System☆

Origin of superconductivity suppression in (Dy{sub 1{minus}x}Pr{sub x})Ba{sub 2}Cu{sub 3}O{sub 7} studied by soft-x-ray absorption spectroscopy

Effect of an Al2O3 transition layer on InGaN on ZnO substrates by organometallic vapor-phase epitaxy