The structure of these materials is determined by the amount of oxygen present. The x in the chemical formula YBa 2 Cu 3 O 7-x represents this non-stoichiometry. When x = 1, the O (1) sites in the Cu (1) layer are empty, resulting in a tetragonal structure. YBCO in its tetragonal form is insulating and does not superconduct. As x decreases, O (2) atoms from the lattice replace some of the Y (3+) ions, giving rise to a reduced density of states at the Fermi level for these O (2-) anions. This reduction of local moments on the Y (3+) ions leads to a decrease in the magnetic response of the material, as observed by NMR studies.
As x further decreases, some of the O (2-) anions become incorporated into the Cu (1) plane itself. Now there are no free holes to carry electrical current, so these crystals become conducting. For YBCO with x near 0, almost all the oxygen is in the form of oxygens that are incorporated into the crystal structure. These materials are called "oxygen-deficient".
The phase diagram for YBCO shows that it becomes metallic when x is less than about 0.5. Above this value, the material becomes a ceramic with no measurable conductivity. It is thought that below a certain critical concentration of vacancies or impurities, charge carriers can diffuse through the material so that it becomes conducting even though most of the oxygen has been removed.
YBCO is a crystalline material, and the optimum superconductive qualities are produced by carefully controlling the annealing and quenching temperature rates. The higher the rate of heat removal during cooling, the more perfect are the crystals that are grown.
When electricity passes through a magnetic field, it becomes magnetism. When light passes through a transparent conductor, it becomes electricity. When current passes through a superconductor, there is no resistance. This is why a superconductor is used in a power line to reduce energy loss due to friction between the wires of the power line.
Superconductivity was first discovered in 1986 by American physicists Joseph E. Hirsch and Kenneth A. George at the University of California, Los Angeles. They were studying a material called "yttrium barium copper oxide" or simply "YBCO", which has many applications in science and technology. When they cooled this material down to -240 degrees Celsius, they found that it became a superconductor-that is, it lost all resistance to current flow.
This material has great potential for use in power transmission lines because it loses none of its strength even when frozen into ice blocks for outdoor use. It also does not get hot when current flows through it.
Ytterbium is an atomic number 70 chemical element with the symbol Yb. At room temperature, ytterbium is a lanthanide, which means it is a solid. Yb, 70. Data are from http://www.webelements.com/yb/index.html.
In physics, Yb has been used as a dopant in glass to create a laser material that is transparent to wavelengths of about 1020 nm. This is below the wavelength of visible light so no light can pass through the material. Yb also has been used as a dopant in glass to create a fluorescent material that emits ultraviolet or violet-blue light upon stimulation by electrons or holes. This is called upconversion fluorescence because the energy of a single photon is enough to excite an electron from its lower to its higher orbital, thus emitting a second photon of longer wavelength. Yb3+ has been used as a phosphor in LEDs to produce white light by combining its blue-green emission with the yellow emission of erbium or terbium. This is called downshifting because the blue-green emission of Yb falls within the spectrum of visible light and so does not need conversion; however, it does need to be shifted toward the red end of the spectrum to make green and yellow.
Yttrium is a silvery white metal that is somewhat soft and ductile. It is relatively stable in air; fast oxidation occurs around about 450 oC (840 oF), producing Y2O3. At higher temperatures, YHfO3 is produced.
Yttrium is used in alloys with other metals because it enhances their strength and hardness while maintaining their elasticity and resistance to corrosion. Alloys containing 70% or more yttrium are called "yttrium-bearing alloys." These alloys are used in armor, weapons, and tools requiring high strength at low weight.
Yttrium has many allotropic forms. Its most common form is yellowish-white metal with a density of about 69% of its liquid form density. Yttrium compounds are widely used as glazes for ceramic dishes and containers due to their attractive color and opacity.
Yttrium is not toxic by itself but some compounds are. Its compounds are generally less toxic than other elements' compounds. For example, YCl3 is highly toxic while Y2O3 is not. This difference is because Cl3- has a large positive charge which causes it to be very reactive with other chemicals, while O3- has no charge and is thus not as likely to cause harm when it binds to another molecule.
Then there's YBCO. This combination of yttrium, barium, copper, and oxygen may be manipulated to generate a chemical with a critical temperature of 93 degrees Celsius. That's still incredibly cold, but it's important to note that it can be achieved with liquid nitrogen rather than liquid helium. The advantage? YBCO is much more affordable than Nb3O5. But even so, it's not suitable for use in high-power applications.
By itself, YBCO has several drawbacks as well. First, it tends to lose its superconductivity above 55 degrees Celsius. That makes it less than ideal for many applications (such as magnetic imaging) that require constant cooling. Second, YBCO loses its structure above 200 degrees Celsius, which means it won't function as an oxide barrier at that point.
However, these issues can be resolved through careful design. For example, you can incorporate YBCO into structures called "pseudomorphic devices" that work at low temperatures. These can include sensors, transducers, and actuators.
Finally, YBCO is also known as a "high-Tc superconductor". That means it has a very high critical temperature compared to other materials used for this purpose. In fact, some studies have shown that YBCO could one day lead to superconductors with temperatures approaching 100 degrees Kelvin (–210 degrees Celsius or 373 degrees Fahrenheit).