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Life would cease to exist without the existence of some elements in the periodic table. However, life would continue even if yttrium did not exist. While yttrium is not known to exhibit any significant biological function, its compounds have helped provide some modern-day comforts, such as color television and wireless communication. On a personal level, yttrium is the one element that has left a long-lasting imprint on me.

When I was a young boy in Taiwan, I dreamed of building a machine that would move forever once started. I had been fascinated by science fiction writings based on such a machine. I still remember the countless nights in pursuit of such a dream. I connected in parallel the two identical motors that I built and prayed that once one was rotated as the generator, it would produce enough power to keep the other rotating without stopping. Clearly, I failed.

Only later did I learn that one cannot fool Mother Nature. By virtue of the second law of thermodynamics, a perfect machine cannot exist. However, as I grew older, I also learned that perpetual motion is not impossible in the quantum domain, that is, in the microscopic atomic scale. For example, electrons move without friction inside an atom and will never stop, similar to a perpetual machine, although at a microscopic dimension.

LEVITATION A magnet disk rotates in mid-air above a YBCO disc that is cooled by liquid nitrogen.
Nature has been kind to us. In 1911, she revealed to Kamerlingh Onnes that such an effect could also occur in a macroscopic object, known as a superconductor. A stream of electrons or an electrical current, once started, will flow forever in a ring made from a superconductor, the closest thing to a perpetual machine. It was superconductivity that first introduced me to yttrium and has kept me off the street for the past several decades.

The zero resistivity of a superconductor enables the transmission of an electrical current without energy loss. As a result, scientists recognized the technological promise that superconductors held immediately after discovery. One can envision a superconducting magnetic, levitated train gliding smoothly above a track at a speed faster than 500 km per hour; a superconducting generator three to six times smaller and lighter than its nonsuperconducting counterpart, producing the same amount of power without loss; a superconducting magnet generating a strong steady field that cannot be otherwise achieved for research and industry; superconducting sensors with unrivaled sensitivity; and electronic devices with ultrafast speed. Unfortunately, during my graduate school years, superconductivity occurred only at temperatures below 23 K close to absolute zero (0 K). To reach such low temperatures, one must use the rare, expensive, and difficult-to-handle liquid helium as a coolant, making application of superconductors impractical.

For decades after 1911, one main goal for scientists in the field of superconductivity was to look for materials that are superconducting at higher temperatures or that possess higher transition temperatures (Tc). Although yttrium is a metal that is not superconducting at ambient pressure, its carbon compound, Y2C3, doped with titanium has a Tc as high as 14.5 K. Until the mid-1980s, the compound was considered a high-temperature superconductor and attracted the attention of many scientists, including myself.

A new, record-high Tc of 35 K was discovered in La2CuO4 slightly doped with La by Alex Mueller and J. Georg Bednorz in 1986. My students and I detected superconductivity at 90 K in LaBa2Cu3O7 (LBCO) in mid-January 1987. Unfortunately, the LBCO sample was unstable because of the impurity present, and thus the superconductivity observed disappeared the next day. Our high-pressure data suggested that a smaller trivalent element than La should alleviate the instability impasse. In late January 1987, my group at the University of Houston and the group led by my former student Maw-Kuen Wu at the University of Alabama observed superconductivity at 93 K in the stable compound YBa2Cu3O7 (YBCO).

The discovery of superconductivity in YBCO above the temperature of liquid nitrogen has ushered in the new era of high-temperature superconductivity. It has made many superconductivity applications conceived decades ago more practical, since one can use plentiful, inexpensive, and easy-to-handle liquid nitrogen. It has opened up new frontiers for scientists to explore.

Who would have dreamed the wonderful world of high-temperature superconductivity would be initiated by yttrium?

Paul C. W. Chu is the T. L. L. Temple Chair of Science at the University of Houston, principal investigator at the Lawrence Berkeley National Laboratory, and president of the Hong Kong University of Science & Technology. Along with Maw-Kuen Wu, Chu discovered the first superconductor above liquid-nitrogen temperature. He received the National Medal of Science in 1988.


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Copyright © 2003 American Chemical Society

Name:Named after Ytterby, Sweden, which yielded many unusual minerals.
Atomic mass:88.91.
History: Discovered in 1789 by Finnish chemist Johann Gadolin.
Occurrence: Yttrium occurs in nearly all rare-earth mineral ores.
Appearance:Silvery white, soft metal.
Behavior: Yttrium is stable in air and is very reactive with the halogens. It is mildly toxic by ingestion.
Uses:Used in X-ray filters and superconductors. Yttrium oxide is combined with europium to give the red phosphor in color television tubes.

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