Possible superconductivity at 109 K in YBaCuO materials
P.Udomsamuthirun 1,2,T.Kruaehong 1 ,T. Nilkamjon 1,2 and S. Ratreng 1,2
1 Prasarnmitr Physics Research Unit, Department of Physics, Faculty of Science,
Srinakharinwirot University, Sukumvit 23,Bangkok,10110,Thailand.
2 Thailand Center of Excellence in Physics(ThEP), Si Ayutthaya Road,
New YBaCuO superconductors are synthesized by using the standard
solid state reaction method as Y5-6-11, Y7-9-16, Y5-8-13, Y7-11-18, Y156, Y3-8-11,
and Y13-20-23. We find that all material obtained show the Meissner effect at
77 K. The resistivity measurements were made by the four-probe method. The
Y 7-11-18 has the highest Tc onset at 109 K. The XRD spectra showed that
they have the same crystal structure as Y123 with some impurities peaks.
In 1986 Bednorz and Muller  found the first high temperature
superconductor in the compound La214, which showed a transition temperature ( Tc) above 30 K. And in 1987 the transition temperature of YBa2Cu3O7 (Y123) was
increased to around 92 K by Chu and co-workers. The researchers have been carried
out on the YBaCuO-family compound like Y123, YBa2Cu4O8 (Y124), and
Y2Ba4Cu7O15 (Y247) to find a higher Tc in the YBaCuO-family. They found that
Y124 and Y247 became superconductive at 80 K and 40K, respectively.
Y247 exhibits a superconductive transition with Tc ranging from 30 to 95 K,
depending on the oxygen content[5,6].
Recently Aliabadi, Farshchi and Akhavan  found the new Y-based high
temperature superconductor Y3Ba5Cu8O18 (Y358) became superconductive at
102 K. And they also proposed that in order to have a stronger superconductor with higher Tc in the YbaCuO family one should pump more holes from the chains to the oxygen sites of the planes, tending to diagonal charge order. Y123 has two CuO2 planes and one CuO chain. Y124 has one CuO double chain. Y247 has one CuO2 planes and one CuO chain, and one double chain. Y358 has a crystal structure similar to Y123 with five CuO2 planes and three CuO chains. The increasing number of CuO2 planes and CuO chain have important effect on the Tc of Y358.
The YBaCuO-family have shown the different in their number of CuO2 planes and
CuO chains or double chains that believed to be the carrier reservoirs. However,
Nakajima et al. had proposed the limited increase in the number of the CuO2
planes in all high-Tc cuprate superconductors to three.
We [also] think that there should be a relationship between the superconductors in YBaCuO family. Assumptions about the relationships in these material are made and we synthesized the new superconductors in this family by using our assumptions. We find new YBaCuO superconductors in 7 formulations with a difference in critical temperature in each.
2. Experimental assumptions
We know that the YBaCuO-family are consists of Y123,Y124,Y247 and
Y358 with the Y358 is the highest Tc of this family . The Y123 and Y358 are shown the similar crystal structure . Aliabadi,Farshchi and Akhavan  proposed that the lattice parameters, a and b , of Y123 is very close to of Y358 but the lattice parameters, c ,of Y358 is almost 3 time of Y123 . Y123 has two CuO2 planes and one CuO chain and Y358 have five CuO2 planes and three CuO chains. Y358 have five CuO2 planes that 2.5 time of the CuO2 planes of Y123 . We think that three parameters should have some relations as
1.the number of CuO2 planes and number of Ba-atoms.
2.the number of CuO chains and the number of Y-atom.
3.the number of Ba-atom plus Y-atom are equal to the number of Cu-atom.
The relation between the number of CuO2 planes and number of Ba-atom,
and the number of CuO chains and the number of Y-atom can not be proven in this
paper. However, the number of Ba-atom plus Y-atom equal to the number of Cu-atom
can be done experimentally. In Y123, there is 1 Y-atom and 2 Ba-atoms so we
get 3 Cu-atoms. In Y358, there are 3 Y-atom and 5 Ba-atoms so we get 8 Cu-atoms.
So we think that the main ideal to synthesize a new superconductor in this family is the number of Ba-atom plus Y-atom equal to the number of Cu-atom.
To reach the highest Tc, we should pump more holes in this family. As our
relation that the number of CuO2 planes relate to number of Ba-atom . We need
more CuO2 planes so we will not do anything to Ba-atom. To make holes, the
number of Y-atom should be missing. This concept are agreed with the assumption to synthesize Y123 that replacing the La-atom by Y-atom in BaCuO2 perovskite; Y 3+ has an ionic radius smaller than La3+ ; and the Tc is higher. We make the assumption that the number of Y-atom should be missing to create more holes to higher the critical temperature. .
At this point, we can make the assumptions to synthesize new
superconductors in the YBaCuO-family as
1.the number of Ba-atom plus Y-atom are equal to the number of Cu-atom.
2.the number of Y-atom can be missing to reach the higher Tc but the 1st
assumption must be obeyed.
The Y123 and Y358 can be explained by our assumption as Y123 is no Y-
atom missing and Y358 is 1 Y-atom missing every 5 Ba-atom.
According to our assumptions, there are many new superconductors will be
found. Example, In case of 1 Y-atom missing ,the general formula should be
Yx-2 BaxCu2x-2Od . The Y358 is the example of this group which has the percent of Y
atoms missing to the number of Ba-atom as x100 = 20% . The 2 Y-atoms missing, the
general formula should be Yx-3 BaxCu2x-3Od . We can get Y5-8-13 with the percent of
Y-atom missing to number of Ba-atom as x100 = 25% .
To prove our assumptions, we synthesize a new group of YBaCuO
superconductors by using the standard solid state reaction method. Appropriate
stoichiometric ratios of powder of Y2O3 , BaCO3 and CuO are mixed, ground, and
react in air at 950 C for 24 hours, and then cooled to 100 C. Calcination is repeated twice
with intermediate grinding. The powders are reground , pressed into pellets 30 mm in
diameter and about 5 mm thickness under 2000 psi pressure. Finally, the samples
obtained are sintering at 950 C for 24 hours and annealed at 500 C for 24 hours in
air. At this point we are not interested in the effect of oxygen-doping. So we obtained all
samples via air annealing.
We first tested the superconductive state by using the Meissner effect at 77 K
and find that all materials obtained show the Meissner effect as Table 1. This
means that all of our samples are superconductors with the critical temperature above
Table 1. Shown the new YBaCuO -superconductors synthesized .
The resistivity measurements were made using the four-probe method. All samples
show the fact that with increasing measuring current the onset of resistivity drop are
shifted to lower temperature. The current densities J =2.55x103 A/m2 used are
shown in Figure 1. And the normalized resistivity versus temperature are shown in
Figure 2. The summation of the Tc off-set , Tc middle and Tc onset of our samples
read from Figure 2 are shown in Table 2.
Table 2. The summation of the Tc of our samples.
We find that the highest Tc onset is 109 K that of Y7-11-18.and Y156 is the
lowest Tconset that 95 K. Y3-8-11 is the highest Tcoff-set , 98 K.
We preliminary survey the crystal structure of our samples. By comparing the
XRD spectra from 100 to 900 of our new superconductors with our Y123 spectra,
they shown that the main peaks are the ones which exist in Y123 with some
impurities peak . We find that there is the one of main peak at about 15 0 that do not
included in the Aliabadi,Farshchi and Akhavan  s calculation of Y358. We find
that our samples are shown the same crystal structure of Y123 with some impurities
peaks that occur by the missing of Y-atom in some planes agreed with our
4.Result and Discussion
We make the assumptions to synthesize a new superconductor in YBaCuO family as the number of Ba-atom plus Y-atom are equal to the number of Cu-atom
and the number of Y-atom can be missing to reach the higher Tc but the 1st
assumption must be obeyed. The new formula of YBaCuO superconductors are
synthesized by using the standard solid state reaction method as Y5-6-11, Y7-9-16,
Y5-8-13, Y7-11-18, Y156, Y3-8-11, Y13-20-33. The Y 7-11-18 has the highest Tc
onset at 109 K. Our samples are shown the same crystal structure as Y123 with
some impurities peaks that occur by the missing of Y-atom in some planes agreed
with our assumptions.
The effect of oxygen-doping on superconductors is not considered in this
Paper. That may be the one of the main parameters to increase the critical
temperature. We think that the highest Tc superconductor may be found by using our
assumptions and optimize doping. More experimental detail will reveal the
mechanism of superconductivity in this material.
We find the assumptions to synthesize a new superconductor in YBaCuO family with the higher Tc. The new formula of YBaCuO superconductors are synthesized by using the standard solid state reaction method as Y5-6-11, Y7-9-16,
Y5-8-13, Y7-11-18, Y156, Y3-8-11, Y13-20-33. The Y 7-11-18 shown highest Tc onset as 109 K. Our samples show the same crystal structure as Y123 with some impurities peaks that occur by the missing of Y-atom in some planes agreed with our assumptions.
The authors would like to thank Professor Dr.Suthat Yoksan for the useful
discussion and also thank the Office of Higher Education
Commission, Faculty of Science Srinakharinwirot University,and ThEP Center for the
 J.G.Bednorz and K.A.Muller,Z.Phys. B 64(1986) 189.
C.W.Chu,Phys.Rev.Lett. 58(1987) 908.
L.J.Martinez-Miranda,Nature 334(1988) 660.
Nature 336(1988) 596.
 J.Karpinski,S.Rusiecki,B.Bucher,E.Kaldis,E.Jilek,Physica C 161(1989)618.
 J-Y.Genoud,T.Graf,G.Triscone,A.Junod,J.Muller,Physica C 192(1992)137.
 A.Aliabadi,Y.A.Farshchi and M.Akhavan,Physica C 469(2009)2012-2014.
H.Iwasaki,Y.Muto,Physica C 158(1987)471.
Figure 1 The resistivity versus temperature are shown.
Figure 2 The normalized resistivity versus temperature are shown.