Phase.1 History of Superconductivity
In 1987, Fujikura's superconductivity development started with a superconducting current level of a few amperes.
In 1911, when Kamerlingh Onnes measured the electric resistance of mercury with liquid helium he successfully produced for the first time by devolatilizing helium, he happened to find a phenomenon where the electric resistance suddenly dropped to zero at -269°C (4.2 K). This is the first discovery of a superconductivity phenomenon. Although it was an epochal discovery, attempts to put the phenomenon to practical use did not produce any results following the discovery. In the 1960s, attempts to process superconducting materials such as Nb-Sn, Nb-Zr, and NB-Ti into wires finally began. The most important characteristic of superconducting wires is that they carry a great electric current without electric resistance. Focusing on this characteristic first, approaches were made to bring a "powerful magnet" into reality.
The next epochal event was the discovery of an oxide superconductor in 1986. It started with the research of "strontium titanate" by J. Georg Bednorz and K. Alex Muller at IBM Zurich Research Laboratory. This insulator substance is well known as a ferroelectric substance, and it looked as though La-Ba-Cu-O (perovskite-based) started decreasing resistance in the neighborhood of 30 k and reached a resistance of 0 at 10 k or lower. They unveiled those results at a conference in Germany, but nobody appreciated them. In the meantime, in April 1986, they contributed their research paper to a German magazine called "Zeitschrift fur Physik," and at least a few additional tests were performed on the results in the world following publication of this paper. After these tests, the Tanaka group in the University of Tokyo identified the crystal structure of the substance and confirmed the Meissner effect. The group proved that the superconductivity phenomenon occurred in a La-Ba-Cu-O-based structure at levels where even the slightest doubt was impossible. On November 13, 1986, the Tanaka Research group determined the existence of superconductivity. The presentation of the result to the Materials Research Society in Boston on December 5 astonished the world, and feverish attempts to search for high-temperature superconductivity subsequently continued over a few fears. In February 1987, a class of Y-Ba-Cu-O (Y-based superconductor) that was displaced at 90 k was discovered, which meant that the critical temperature (Tc) increased by 60 k in such a short period of time. Higher superconductivity displacement temperatures were found in succession after that, and as of 2004, the displacement temperature under high pressure for mercury-based cuprates is "160 Kelvin." This is the best record.
Due to the February 1987 discovery of an YBa2Cu3Ox superconductor (the critical temperature: 90 k), the critical temperature exceeded the temperature of liquid nitrogen (77 k) for the first time. In the same year, a BiSrCaCuO-based superconductor was discovered and many research organizations then accomplished a critical current density of 1,000,000 A/cm2, which was a practical level, on a monocrystalline substrate by using an YBaCuO superconductor. At this time, Fujikura attempted to develop superconducting wires. The first development was wire with a radius of 1 mm, made by putting YBCO superconducting powder into a stainless pipe and sintering it. The superconducting current in liquid nitrogen, however, was only at a level of a few amperes.