Yttrium barium copper oxide
Encyclopedia : Y : YT : YTT : Yttrium barium copper oxide
| Yttrium barium copper oxide | |
|---|---|
| |
| General | |
| Systematic name | Yttrium barium copper oxide |
| Other names | YBCO, Y123, yttrium barium cuprate |
| Molecular formula | YBa2Cu3O7−x |
| Molar mass | Variable. |
| Appearance | Black solid. |
| CAS number | [107539-20-8] |
| Properties | |
| Density and phase | ? g/cm3, solid |
| Solubility in water | Insoluble |
| Melting point | ?°C (? K) |
| Structure | |
| Coordination geometry | Cubic. |
| Crystal structure | Based on the Perovskite structure. |
| Hazards | |
| EU classification | Irritant (I). |
| NFPA 704 | |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related high-Tc superconductors | ? |
| Related compounds | Yttrium(III) oxide Barium oxide Copper(II) oxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
History
Superconductivity was first observed in 1911 when Heike Kamerlingh Onnes was investigating the resistance of mercury cooled in liquid helium. Onnes observed that the resistance of mercury disappeared when its temperature reached that of liquid helium, Tb = 4.2 K. Heike's discovery launched a flurry of research into superconducting materials.Seventy-five years later, Georg Bednorz and Alex Müller, working at IBM in Zurich Switzerland, discovered that certain semiconducting oxides became superconducting at the then relatively high temperature of 35 K. Bednorz and Müller found a motif for high temperature superconductors in lanthanum barium copper oxide. This motif requires a material to have an oxygen deficient perovskite crystal and contain copper in a +2/+3 mixed valancy.
Using the motif discovered by Bednorz and Müller, Maw-Kuen Wu and his graduate students, Ashburn and Torng[#endnote_apsn] at the University of Alabama in Huntsville in 1987, discovered YBCO. The rapid succession of new high temperature superconducting materials discovered by these groups ushered in a new era in material science and chemistry.
YBCO was the first material to become superconducting above 77 K, the boiling point of nitrogen. All materials developed before YBCO became superconducting only at temperatures near the boiling points of liquid helium or liquid hydrogen (Tb = 20.1 K). The significance of the discovery of YBCO is the break through in the refrigerant used to cool the material to below the critical temperature.
Synthesis
YBCO was first synthesized by mixing the metal carbonate precursors together and reacting them at temperatures between 1000 K to 1300 K.[#endnote_hous][#endnote_earn]
- 4BaCO3 + Y2(CO3)3 + 6 CuCO3 → 2 YBa2Cu3O + 13 CO2
The superconducting property of YBCO is very sensitive to its oxygen present. Only those materials with 0 ≤ x ≤ 0.5 are superconducting below Tc, and when x ~ 0 the material superconducts at the highest temperature, 95 K.[#endnote_earn]
In addition to being sensitive to the amount of oxygen, special care must be taken to sinter YBCO. YBCO is a crystaline material, and the best superconduction performance is obtained when crystal grain boundaries are aligned by careful control of annealing and quenching temperature rates.
Numerous other methods to synthesize YBCO have developed since its discovery by Wu and his coworkers, such as chemical vapor deposition (CVD)[#endnote_hous][#endnote_earn], sol-gel[#endnote_yang], and aerosol[#endnote_harv] methods. These alternative methods, however, still require careful sintering to produce a quality product.
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Structure
YBCO is a defect perovskite. The perovskite structure of YBCO consists of layers. The boundary of each layer is defined by planes of square planar CuO4 units sharing 4 vertices. The planes can some times be slightly puckered[#endnote_hous]. Perpendicular to these CuO2 planes are CuO4 ribbons sharing 2 vertices. The yttrium atoms are found between the CuO2 planes, while the barium atoms are found between the CuO4 ribbons and the CuO2 planes. This is illustrated in the figure below.
Applications in technology
Several commercial applications of high temperature superconducting materials have been realized. For example, superconducting materials are finding use as magnets in magnetic resonance imaging, magnetic levitation, and Josephson junctions.However, YBCO has yet to be used in many applications involving superconductors. This is primarily due to three problems. The first and most obvious problem is the temperature required for superconduction. Cooling materials to liquid nitrogen temperature is not feasible on a large scale.
Second, YBCO has a very low critical current density, ie only a small current can be passed while maintaining superconductivity. This problem is due to crystal grain boundaries in the crystaline material. The grain boundary problem can be controlled to some extent by preparing thin films via CVD or by texturing the material to align the grain boundaries.
A third problem limiting using this material in technological applications is associated with processing of the material. Oxide materials such as this are brittle, and forming them into wires is difficult.
The most promising method developed to utilize this material involves CVD of YBCO on flexible metal tapes coated with zirconium oxide, ZrO2.
Surface modification of YBCO
Surface modification of materials has often led to new and improved properties. Corrosion inhibition, polymer adhesion and nucleation, preparation of organic superconductor/ insulator/high-Tc superconductor trilayer structures, and the fabrication of metal/insulator/ superconductor tunnel junctions have been developed using surface modified YBCO[#endnote_xuet].These molecular layered materials are synthisized using cyclic voltammetry. Thus far YBCO layered with alkylamines, arylamines, and thiols have been produced with varying stability of the molecular layer. It has been proposed that amines act as Lewis bases and bind to Lewis acidic Cu surface sites in YBa2Cu3O7 to form stable coordination bonds.
Magnetic levitation
Similar to all superconductors, YBCO displays the Meissner effect as it is cooled and reaches its critical temperature. At the critical temperature and below, YBCO becomes perfectly diamagnetic and excludes all magnetic fields from passing through it. YBCO does this by developing an internal magnetic field that perfectly balances the externally applied magnetic field. This causes any magnet on the surface of the superconductor to levitate[#endnote_hous].References
- ↑ Cathrine Housecroft, Alan Sharpe. Inorganic Chemistry. Second Edition. Pearson Education Limited. Essex, England. 2005
- ↑ Earnshaw, Greenwood. Chemistry of the Elements. Second Edition. Elsevier Butterworth-Heinemann. New York. 2005
- ↑ http://www.aps.org/apsnews/0703/070312.cfm
- ↑ Xu et al. Langmuir, 1998, 14 (22)
- ↑ Yang-Kook Sun, In-Hwan Oh Ind. Eng. Chem. Res. 1996, 35, 4296
- ↑ http://adsabs.harvard.edu/abs/1991PhDT........28Z
External links
- http://www.ch.ic.ac.uk/otway/YBCO.html
- [Superconductivity in everyday life : Interactive exhibition].
- [External MSDS Data Sheet].
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
Media
- [Superconducting levitation of YBCO] ([file info])
- Problems seeing the videos? See .
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