Talk:Yttrium barium copper oxide

structure diagrams
The diagram in the "structure" section appears to be wrong. It disagrees with the description, with the 3-D diagram at the top of the page, and with the article on perovskite structure.

In particular: the copper atoms and the oxygen atoms should be switched. If Barium is the center of a cube, then copper should be at the vertices of the cube, and oxygen at the middle of each edge.

Note: I'm saying the yellow dots need to be swapped with the red dots. Just changing the legend would be a bad idea, since we should stick with the convention of using small red dots for oxygen. --Tim314 16:44, 18 September 2006 (UTC)


 * Good catch. I wonder how many people that's confused. I've nominated the image for deletion, because I don't see a good way to fix it without starting over from scratch. —Keenan Pepper 19:55, 20 September 2006 (UTC)

The figure is easily fixed using photoshop. Either of you want to take a shot at it, or should I? Rich 21:24, 11 October 2006 (UTC)


 * Was image changed ? In June 2008 both seem to match the description at perovskite. Rod57 (talk) 19:47, 11 June 2008 (UTC)

Discovery
Paul Chu's group in Houston is credited with the discovery of YBCO and should be listed first.

Counterpoint: In an article entitled History of Original Ideas and Basic Discoveries in Particle Physics (High Temperature Superconductivity, Plenum Press), Paul Chu, recounting the discovery, wrote:


 * ...I received an exciting call from Maw-Kuen [Wu] from UAH at about 5 p.m., January 29, 1987. He informed me that he and his students, Jim Ashburn and C. J. Torng, had just observed a reversible R [resistivity]-drop starting at above 90 K and finishing at about 77  K in two of their samples.  All of us were ecstatic, since stable and reversible superconductivity might have finally been achieved, provided a Meissner effect could be detected.  Right before he called me, Maw-Kuen had also phoned Peiherng about their exciting observation.  Without divulging information about the elements of their samples, Maw-Kuen told Peiherng, "We just did what we discussed previously (in Houston in early January)."  Peiherng, Ruling and I reviewed all our previous data and decided to make a few new samples containing the newly arrived Y and Yb oxides.  Unfortunately, we failed to see any stable superconductivity at 90 K.  Maw-Kuen and Jim arrived at Houston the next morning of January 30 with their samples which had a nominal formula of Y1.2Ba0.8CuO4 (YBCO).  We subjected them to a thorough battery of tests. Indeed, R decreased rapidly, starting at ~93 K and reached zero at ~80 K, as was first observed at Huntsville by Maw-Kuen and his students.  By the end of the day, we completed the magnetic measurements.  A distinct diamagnetic shift characteristic of a superconducting transition started at ~91 K.  The results are shown in Figs. 8 and 9.  The expected downward shift of Tc [critical temperature] toward lower temperatures in the presence of a magnetic field was also observed. Following the recipe of Maw-Kuen, several samples were also made in Houston and tested on January 30.  Most showed the 90 K superconductivity.  The long-sought-after stable and reproducible superconductivity above the liquid nitrogen boiling point of 77 K had been discovered...

Thus, despite the fact that many sources credited Chu with the idea behind the discovery, his own account suggests otherwise. It should also be noted that on the paper published jointly by UAH and UH, the Alabama-Huntsville team was listed first.

Coordination Geometry
Is not Cubic. Should be ortho Rhombic the lattice constants a does not = b does not = c


 * in YBCO a is very similar to b at 0.382 and 0.389 nm respectively, so for "high school science" one can assume a=b. By the way, c is 1.168 nm.

LMB (talk) 09:46, 6 November 2008 (UTC)

Related Compounds
R Ba2 Cu3 O(7-delta) where R is a rare earth element Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

I am surprised this page quotes YBa2Cu3O7 as it as a defect ceramic material, not a molecular compound - in all cases. —Preceding unsigned comment added by 125.7.52.129 (talk) 04:19, 29 September 2008 (UTC)

Density
the density of thin films is 6.38 gm/cm^3 for bulk material it is less.

applications
YBCO does not have a small critical current density. It is used commercially for high current carrying tapes and High Tc SQUID's.

Ref. 10 is not authoritative or correct, modern cryogenic NMR probes are cold copper, not superconductors.


 * A critical current density at least for single cristal bulk should be given.

Magnetic Levitation
YBCO is a type 2 superconductor and only expels magnetic field up to a certain strength called Hc1. after this value is reached magnetic field penetrates the superconuctor in the form of vortices. Anon - sometime.

This section of the article applies to all superconductors and should be moved there is not already there. Rod57 (talk) 23:45, 4 September 2008 (UTC)

levitation
The levitation of a magnet above YBCO has nothing to do with the Meissner-effect. The Meissner-effect only occurs in Type I superconductors as the magnetic field is expelled from the superconductor. In order for a magnet to levitate, it is required that magnetic flux lines may "pin" into the material (pinning effect). The magnet would just fall off otherwise. Thus the magnetic levitation is an effect of type II superconductors and has nothing to do with the Meissner effect.

Fat kanickel 14:40, 12 December 2006 (UTC)fat_kanickel

The Meissner effect does occur in type II superconductors, but only below Hc1. Between Hc1 and Hc2 the Meissner effect is said to be incomplete. See Charles Kittel, Introduction to Solid State Physics. JHobbs103 (talk) 18:18, 2 May 2009 (UTC)

This article contains a spurious and highly misleading reference to the Meissner effect. The levitation in the video cannot be said to demonstrate the Meissner effect. The only way that it could be demonstrated is if a magnet was placed on top of the superconductor, then it was cooled and THEN it was observed to spontaneously levitate. That WOULD demonstrate the Meissner effect. The Meissner effect is the ejection of a WEAK field as it passes below the transition temperature. Once ejected, flux is kept out by Lenz's law and Faraday's law as applied to a perfect conductor. This ejection cannot be explained by Maxwell's equations and was not anticipated when it was experimentally observed by Meissner. The Meissner effect can only be fully explained by using quantum mechanics. For all these reasons it is a separate phenomena and must be carefully distinguished from Lenz's law and Faraday's law as applied to a perfect conductor. —Preceding unsigned comment added by 92.29.64.218 (talk) 14:11, 21 February 2010 (UTC)

More explanation please
What does T represent in this sentence: 120 T for B perpendicular and 250 T for... Mrshaba (talk) 21:40, 3 Jul 2008 (UTC)
 * Disregard question. I linked T to the unit page. Mrshaba (talk) 21:49, 3 July 2008 (UTC)

"upper critical field" is unimportant
Regarding the sentence Its upper critical field is 120 T for B perpendicular and 250 T for B parallel to the CuO2 planes.

...I'd like to comment that Hc2 is unimportant in Type II superconductors, because before Hc2 can destroy the superconducting phenomenon, there's the much smaller (ca. 10..20T) Hirr, or 'irreversibility field', which causes the magnetization loop to reverse. The area between Hirr and Hc2 has vortices, but is completely useless from the industrial use point of view. LMB (talk) 10:15, 6 November 2008 (UTC)

Coordination polyhedra
I've made a few images of the unit cell and of the coordination geometry of each metal atom in YBa2Cu3O7-$\delta$. If these are useful, I can provide similar polyhedra for the five different oxygen environments.

Ben (talk) 20:13, 20 January 2009 (UTC)

Um... First, yes, these look extremely useful, why not to put them into the text, in the structure section? Second though, are they correct? The full structure appears to have three CuO2 planes, instead of one CuOx and two CuO2... I would assume the polyhedra would need to get modified if the structure is corrected? Would also be nice to put some text discussing which CuOn polyhedra go with which geometry. Generally, a little improvement to the structure section would be desirable, right now the two types of CuOx planes are being referenced without ever having been defined (this, of course, does not relate to Ben's suggestion). 12.104.156.31 (talk) 20:30, 20 November 2012 (UTC)


 * Fair point, I think this must be crystallographic disorder in the literature structure I used. Thanks for spotting these errors. I've updated the article, only 12 years late. --Ben (talk) 16:43, 6 April 2021 (UTC)

History
I have redone a bit the wording for the discovery by müller and bernorz. i found it to be somewhat weird, saying that one of the SC that they discovered had 35k Tc and then talking about LBCO without saying it is that one that become SC at 35k. I think it is more clear now, although i am pretty sure it could be more elegant, english is not my maternal tongue.

Not 200 times that of copper
I deleted the claim that "Amperium superconductor wire exhibits conductivity approximately 200 times that of copper wire of similar dimensions," for two reasons: GPS Pilot (talk) 10:31, 4 February 2016 (UTC)
 * It makes no sense, as the conductivity of a superconductor is infinite.
 * The cited source ( http://www.nature.com/news/2010/101008/full/news.2010.527.html ) makes no mention of either Amperium or conductivity.

Meissner effect figure misleading
The figure/movie in the "proposed applications" section showing the levitating vessels containing YBCO uses the caption "Like all superconductors, YBCO displays the Meissner effect."... As true as this may be, the levitating YBCO (and almost all similar levitation demonstrations, except for magnets floating above lead or niobium bowls) is not an example of the Meissner effect, but rather of flux pinning. While closely related phenomena, there is an important distinction between expelling all flux lines from the bulk (Meissner) and allowing flux lines to penetrate but force them to remain fixed (pinning). This isn't just nitpicking -- the pinning keeps the samples levitating stably at constant height/transverse position with respect to the track (and from falling off) while in the Meissner state the sample would just be pushed away from the track. (You can't do this sort of thing with lead.)

So I'm going ahead and changing it; please change my new version if you don't like it (but hopefully not to the Meissner explanation). Lambda(T) (talk) 21:49, 12 April 2017 (UTC)