 | |
 | |
| Names | |
|---|---|
| IUPAC name barium copper yttrium oxide | |
| Other names YBCO, Y123, yttrium barium cuprate | |
| Identifiers | |
| ChemSpider | |
| ECHA InfoCard | 100.121.379 |
| EC Number |
|
| Properties | |
| YBa2Cu3O7 | |
| Molar mass | 666.19 g/mol |
| Appearance | Black solid |
| Density | 6.4 g/cm3[1][2] |
| Melting point | >1000 °C |
| Insoluble | |
| Structure | |
| Based on theperovskite structure. | |
| Orthorhombic | |
| Hazards | |
| GHS labelling: | |
 | |
| Warning | |
| H302,H315,H319,H335 | |
| P261,P264,P270,P271,P280,P301+P312,P302+P352,P304+P340,P305+P351+P338,P312,P321,P330,P332+P313,P337+P313,P362,P403+P233,P405,P501 | |
| Related compounds | |
Relatedhigh-Tc superconductors | Cuprate superconductors |
Related compounds | Yttrium(III) oxide Barium oxide Copper(II) oxide |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Yttrium barium copper oxide (YBCO) is a family ofcrystallinechemical compounds that displayhigh-temperature superconductivity; it includes the first material ever discovered to becomesuperconducting above the boiling point ofliquid nitrogen [77 K (−196.2 °C; −321.1 °F)] at about 93 K (−180.2 °C; −292.3 °F).[3]
Many YBCO compounds have the general formulaYBa2Cu3O7−x (also known as Y123), although materials with other Y:Ba:Cu ratios exist, such asYBa2Cu4Oy (Y124) orY2Ba4Cu7Oy (Y247). At present, there is no singularly recognised theory for high-temperature superconductivity.
It is part of the more general group ofrare-earth barium copper oxides (ReBCO) in which, instead of yttrium, other rare earths are present.
In April 1986,Georg Bednorz andKarl Müller, working atIBM in Zurich, discovered that certain semiconducting oxides became superconducting at relatively high temperature, in particular, alanthanum barium copper oxide becomes superconducting at 35 K. This oxide was anoxygen-deficientperovskite-related material that proved promising and stimulated the search for related compounds with higher superconducting transition temperatures. In 1987, Bednorz and Müller were jointly awarded the Nobel Prize in Physics for this work.
Following Bednorz and Müller's discovery, a team led byPaul Ching Wu Chu at theUniversity of Alabama in Huntsville andUniversity of Houston discovered that YBCO has a superconducting transition critical temperature (Tc) of 93 K.[3] The first samples wereY1.2Ba0.8CuO4, but this was an average composition for two phases, a black and a green one. Workers atBell Laboratories identified the black phase as the superconductor, determined its composition YBa2Cu3O7−δ and synthesized it in single phase[4]
YBCO was the first material found to become superconducting above 77 K, the boiling point ofliquid nitrogen, whereas the majority of other superconductors require more expensive cryogens. Nonetheless, YBCO and its many related materials have yet to displace superconductors requiringliquid helium for cooling.
Relatively pure YBCO was first synthesized by heating a mixture of the metal carbonates at temperatures between 1000 and 1300 K.[5][6]
Modern syntheses of YBCO use the corresponding oxides and nitrates.[6]
The superconducting properties of YBa2Cu3O7−x are sensitive to the value ofx, its oxygen content. Only those materials with0 ≤x ≤ 0.65 are superconducting belowTc, and whenx ~ 0.07, the material superconducts at the highest temperature of95 K,[6] or in highest magnetic fields:120 T forB perpendicular and250 T forB parallel to the CuO2 planes.[7]
In addition to being sensitive to the stoichiometry of oxygen, the properties of YBCO are influenced by the crystallization methods used. Care must be taken tosinter YBCO. YBCO is a crystalline material, and the best superconductive properties are obtained when crystalgrain boundaries are aligned by careful control ofannealing andquenching temperature rates.
Numerous other methods to synthesize YBCO have developed since its discovery by Wu and his co-workers, such aschemical vapor deposition (CVD),[5][6]sol-gel,[8] andaerosol[9] methods. These alternative methods, however, still require careful sintering to produce a quality product.
However, new possibilities have been opened since the discovery that trifluoroacetic acid (TFA), a source of fluorine, prevents the formation of the undesiredbarium carbonate (BaCO3). Routes such as CSD (chemical solution deposition) have opened a wide range of possibilities, particularly in the preparation of long YBCO tapes.[10] This route lowers the temperature necessary to get the correct phase to around 700 °C (973 K; 1,292 °F). This, and the lack of dependence on vacuum, makes this method a very promising way to get scalable YBCO tapes.
YBCO crystallizes in adefect perovskite structure. It can be viewed as a layered structure: the boundary of each layer is defined by planes of square planar CuO4 units sharing 4 vertices. The planes can sometimes be slightly puckered.[5] Perpendicular to these CuO4 planes are CuO2 ribbons sharing 2 vertices. Theyttrium atoms are found between the CuO4 planes, while thebarium atoms are found between the CuO2 ribbons and the CuO4 planes. This structural feature is illustrated in the figure to the right.
 |  |  |  |  |
| cubic {YO8} | {BaO10} | square planar {CuO4} | square pyramidal {CuO5} | YBa2Cu3O7- unit cell |
 |  |
| puckered Cu plane | Cu ribbons |
Although YBa2Cu3O7 is a well-defined chemical compound with a specific structure and stoichiometry, materials with fewer than seven oxygen atoms per formula unit arenon-stoichiometric compounds. The structure of these materials depends on the oxygen content. This non-stoichiometry is denoted by the x in the chemical formula YBa2Cu3O7−x. Whenx = 1, the O(1) sites in the Cu(1) layer (as labelled inthe unit cell) are vacant and the structure istetragonal. The tetragonal form of YBCO is insulating and does not superconduct. Increasing the oxygen content slightly causes more of the O(1) sites to become occupied. Forx < 0.65, Cu-O chains along theb axis of the crystal are formed. Elongation of theb axis changes the structure toorthorhombic, with lattice parameters ofa = 3.82,b = 3.89, andc = 11.68 Å.[12] Optimum superconducting properties occur whenx ~ 0.07, i.e., almost all of the O(1) sites are occupied, with few vacancies.
In experiments where other elements are substituted on the Cu and Ba[why?] sites, evidence has shown that conduction occurs in the Cu(2)O planes while the Cu(1)O(1) chains act as charge reservoirs, which provide carriers to the CuO planes. However, this model fails to address superconductivity in the homologue Pr123 (praseodymium instead of yttrium).[13] This (conduction in the copper planes) confines conductivity to thea-b planes and a large anisotropy in transport properties is observed. Along thec axis, normal conductivity is 10 times smaller than in thea-b plane. For othercuprates in the same general class, the anisotropy is even greater and inter-plane transport is highly restricted.
Furthermore, the superconducting length scales show similar anisotropy, in both penetration depth (λab ≈ 150 nm, λc ≈ 800 nm) and coherence length, (ξab ≈ 2 nm, ξc ≈ 0.4 nm). Although the coherence length in thea-b plane is 5 times greater than that along thec axis it is quite small compared to classic superconductors such as niobium (where ξ ≈ 40 nm). This modest coherence length means that the superconducting state is more susceptible to local disruptions from interfaces or defects on the order of a single unit cell, such as the boundary between twinned crystal domains. This sensitivity to small defects complicates fabricating devices with YBCO, and the material is also sensitive to degradation from humidity.
Many possible applications of this and related high temperature superconducting materials have been discussed. For example, superconducting materials are finding use asmagnets inmagnetic resonance imaging,magnetic levitation, andJosephson junctions. (The most used material for power cables and magnets isBSCCO.)[citation needed]
YBCO has yet to be used in many applications involving superconductors for two primary reasons:
The most promising method developed to utilize this material involves deposition of YBCO on flexible metal tapes coated with buffering metal oxides. This is known ascoated conductor. Texture (crystal plane alignment) can be introduced into the metal tape (the RABiTS process) or a textured ceramic buffer layer can be deposited, with the aid of an ion beam, on an untextured alloy substrate (theIBAD process). Subsequent oxide layers prevent diffusion of the metal from the tape into the superconductor while transferring the template for texturing the superconducting layer. Novel variants on CVD, PVD, and solution deposition techniques are used to produce long lengths of the final YBCO layer at high rates. Companies pursuing these processes includeAmerican Superconductor, Superpower (a division ofFurukawa Electric),Sumitomo,Fujikura,Nexans Superconductors,Commonwealth Fusion Systems, and European Advanced Superconductors. A much larger number of research institutes have also produced YBCO tape by these methods.[citation needed]
The superconducting tape is used forSPARC, atokamak fusion reactor design that can achievebreakeven energy production.[15]
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.[16]
These molecular layered materials are synthesized usingcyclic voltammetry. Thus far, YBCO layered with alkylamines, arylamines, andthiols have been produced with varying stability of the molecular layer. It has been proposed that amines act asLewis bases and bind toLewis acidic Cu surface sites in YBa2Cu3O7 to form stablecoordination bonds.
In 1987, shortly after it was discovered, physicist and science authorPaul Grant published in the U.K. JournalNew Scientist a straightforward guide for synthesizing YBCO superconductors using widely-available equipment.[17] Thanks in part to this article and similar publications at the time, YBCO has become a popular high-temperature superconductor for use by hobbyists and in education, as the magnetic levitation effect can be easily demonstrated using liquid nitrogen as coolant.
In 2021, SuperOx, a Russian and Japanese company, developed a new manufacturing process for making YBCO wire for fusion reactors. This new wire was shown to conduct between 700 and 2000 Amps per square millimeter. The company was able to produce 186 miles of wire in 9 months, between 2019 and 2021, dramatically improving the production capacity. The company used a plasma-laser deposition process, on a electropolished substrate to make 12-mm width tape and then slit it into 3-mm tape.[18]
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