Published on Dec 06, 2015
Superconductivity is the phenomenon in which a material losses all its electrical resistance and allowing electric current to flow without dissipation or loss of energy. The atoms in materials vibrate due to thermal energy contained in the materials: the higher the temperature, the more the atoms vibrate.
An ordinary conductor's electrical resistance is caused by these atomic vibrations, which obstruct the movement of the electrons forming the current. If an ordinary conductor were to be cooled to a temperature of absolute zero, atomic vibrations would cease, electrons would flow without obstruction, and electrical resistance would fall to zero. A temperature of absolute zero cannot be achieved in practice, but some materials exhibit superconducting characteristics at higher temperatures.
In 1911, the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in mercury at a temperature of approximately 4 K (-269o C). Many other superconducting metals and alloys were subsequently discovered but, until 1986, the highest temperature at which superconducting properties were achieved was around 23 K (-250o C) with the niobium-germanium alloy (Nb3Ge)
In 1986 George Bednorz and Alex Muller discovered a metal oxide that exhibited superconductivity at the relatively high temperature of 30 K (-243o C). This led to the discovery of ceramic oxides that super conduct at even higher temperatures. In 1988, and oxide of thallium, calcium, barium and copper (Ti2Ca2Ba2Cu3O10) displayed superconductivity at 125 K (-148o C), and, in 1993 a family based on copper oxide and mercury attained superconductivity at 160 K (-113o C). These "high-temperature" superconductors are all the more noteworthy because ceramics are usually extremely good insulators.
Like ceramics, most organic compounds are strong insulators; however, some organic materials known as organic synthetic metals do display both conductivity and superconductivity. In the early 1990's, one such compound was shown to super conduct at approximately 33 K (-240o C). Although this is well below the temperatures achieved for ceramic oxides, organic superconductors are considered to have great potential for the future.
New superconducting materials are being discovered on a regular basis, and the search is on for room temperature superconductors, which, if discovered, are expected to revolutionize electronics. Room temperature superconductors (ultraconductors) are being developed for commercial applications by Room Temperature Superconductors Inc.(ROOTS).Ultraconductors are the result of more than 16 years of scientific research ,independent laboratory testing and eight years of engineering development. From an engineering perspective, ultraconductors are a fundamentally new and enabling technology. These materials are claimed to conduct electricity at least 100,000 times better than gold, silver or copper.
Ultraconductors are patented1 polymers being developed for commercial applications by Room Temperature Superconductors Inc (ROOTS). The materials exhibit a characteristic set of properties including conductivity and current carrying capacity equivalent to superconductors, but without the need for cryogenic support.
The Ultraconductor properties appear in thin (5 - 100 micron) films of certain dielectric polymers following an induced, non-reversible transition at zero field and at ambient temperatures >> 300 K. This transition resembles a formal insulator to conductor (I-C) transition.
The base polymers used are certain viscous polar elastomers, obtained by polymerization in the laboratory or as purchased from industrial suppliers. Seven chemically distinct polymers have been demonstrated to date.
The transition is induced by mild ionization of the films by various methods. It occurs in connection with a relatively slow (hours to days, depending upon the volume) electronic phase separation of the materials. The separation produces two components, a) a near-perfect dielectric bulk phase and b) a highly localized phase having mean charge concentration about 1020 cm-3 or more. The charge-rich phase of the polymer is highly organized and durable, and exhibits a characteristic set of anomalous properties.
After ionization, the film initially exhibits a growing ferromagnetism (more correctly, a superparamagnetism, as measured by magnetic susceptometer), which plateaus at values corresponding to a spin polarized mean charge concentration (for the whole polymer volume) as high as ~ 1018 to 1019 cm-3. This feature is considered to indicate collective quantum mechanical behavior.
Subsequently, discrete microscopic structures - the localized phase - can be observed and imaged (for example, by AFM and EFM) as randomly distributed in the bulk material. A proportion of these structures, typically 1 - 2 microns diameter, extends from substrate to film surface, and can also be electrically contacted. These structures exhibit a characteristic set of measured properties, including highly anisotropic conductivity > 1011 S/cm; current densities > 5 x 108 A/cm2; a zero Seebeck coefficient over the temperature range 87 - 233K; a six orders of magnitude violation of the Wiedemann Franz law; and a near-instantaneous transition to high resistivity at a critical current. The polymers’ conductivity is not measurably temperature dependent over the range 1.8 - 700K, and is stable in magnetic fields at least as high as 9 Tesla.
IR spectroscopy of the post-transition films shows them to be chemically unchanged from the base polymer; that is, the new structures are composed of the same molecular material as the bulk, which remains insulating.
Properties of Ultraconductors
Ultraconductors are the electrical conductors which have certain properties similar to present day superconductors. They are best considered as a novel state of matter. They are made by the sequential processing of amorphous polar dielectric elastomers. They exhibit a set of anomalous magnetic and electric properties including very high electrical conductivity very high electrical conductivity (> 1011 S/cm -1) and current densities (> 5 x 108 A/cm2) over a wide temperature range (1.8 to 700 K).
Additional properties established by experimental measurements include: the absence of measurable heat generation under high current; thermal versus electrical conductivity orders of magnitude in violation of the Wiedemann-Franz law; a jump-like transition to a resistive state at a critical current; a nearly zero Seebeck coefficient over the temperature range 87 - 233 K; no measurable resistance when Ultraconductor(tm) films are placed between superconducting tin electrodes at cryogenic temperatures.
The Ultraconductor properties are measured in discrete macromolecular structures which form over time after the processing. In present thin films (1 - 100 micron) these structures, called 'channels', are typically 1 - 2 microns in diameter, 10 - 1000 microns apart, and are strongly anisotropic in the Z axis. RTS was founded in 1993 to develop the Ultraconductor(tm) technology, following 16 years of research by a scientific team at the Polymer Institute, Russian Academy of Sciences, led by Dr. Leonid Grigorov, Ph.D., Dc.S. There have been numerous papers in peer-reviewed literature, 4 contracts from the U.S. government, a landmark patent (US patent # 5,777,292). and a devices patent (US patent # 6,552,883.) Another patent is pending and a fourth now is being completed. To date 7 chemically distinct polymers have been used to create Ultraconductors(tm), including olefin, acrylate, urethane and silicone based plastics.
The total list of candidate polymers suited to the process is believed to number in the hundreds. In films, these channels can be observed by several methods, including phase contrast optical microscope, Atomic Force Microscope (AFM), magnetic balance, and simple electric contact. The channel structures can be moved and manipulated in the polymer. Ultraconductor(tm) films may be prepared on metal, glass, or semiconductor substrates. The polymer is initially viscose (during processing). For practical application the channels may be "locked" in the polymer, by cross linking, or glass transition. The channel's characteristics are not affected by either mode.
A physics model of the conducting structures, which fits well with the experimental measurements, and also a published theory, have been developed. The next step in material development is to increase the percentage or "concentration" of conducting material. This will lead to films with a larger number of conducting points (needed for interposers and other applications) and to wire. Wire is essentially extending a channel to indefinite length, and the technique has been demonstrated in principle. Connecting to these conducting structures is done with a metal electrode, and when two channels are brought together they connect.
From an engineering point of view, we expect the polymer to replace copper wire and HTS in many applications. It will be considerably lighter than copper, and have less electric resistance.
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