New Crystal

Effect of Pr and Zn on structural parameters in YBa2Cu3O7-δ system Miskil S. Naik, P.R.Sarode, R.B. Prabhu ( Department of Physics, Goa University, Taleigao Pleatau , Goa,403206, India.)

Abstract In this paper we present the refined parameters of Y 1-xPrxBa2 [Cu1-yZny]3O7-δ

using

Rietveld refinement program . Introduction It is known that Zn substitutes at Cu(2) sites in the CuO2 plane . It is a nonmagnetic impurity and degrades Tc by potential scattering which results in pinning the charge stripe .On the other hand Pr substitutes at the Y site and is responsible for forming a narrow band called FR band near the Fermi energy. This band grabs holes from the p-d band in the plane resulting in Tc degradation.

Experimental Procedure Y1-xPrxBa2 [Cu1-yZny]3O7-δ with different values of x and y with x = 0.1 and 0 ≤ y ≤ 0.10 were prepared by solid state reaction method. The oxides of purity 99.99% were taken in the stoichiometric ratio were thoroughly mixed ,grounded and calcined at 9200C in air for a period of 17-20 h. After four intermediate grindings and calcinations in air the obtained precursors were regrounded and pressed into pellets, and sintered in oxygen for 24h at 9400C and then furnace cooled to below 1000 C with an intervening annealing for 24h at 6000C. The samples were then characterized by X-ray diffraction (XRD) using a

Rigaku X-ray diffractometer equipped with CuKα radiation in the range 200-800 and the phase purity of the samples was checked using Rietveld Analysis Program.

Results and Discussion X-ray diffraction patterns of samples of

composition Y1-xPrxBa2 [Cu1-

Zny]3O7-δ with different values of x and y with x = 0.1 and 0 ≤ y ≤ 0.10 were recorded

y

on Rigaku X-ray diffractometer D MaxII-C with CuKα radiation at room temperature. These patterns are shown in Figs. 1 . The structural parameters were refined by Fullprof program. The refinement has been carried out using main YBa2Cu3O7-δ phase as the starting crystal structure with space group Pmmm. Each refined reflection profile is described by Gaussian function. The wavelength of CuKα 1

is set as 1.5405A0 .The

refinement is performed according to the following group order (1) Scale factor, background, zero point shift, (2) Cell parameters, (3) Preferred orientations, (4) atom position parameters, (5) site occupancy. We have presented the refined diffraction patterns for two compositions of Y0.9Pr0.1Ba2 [Cu1- yZny]3O7-δ with y = 0.00 and y = 0.01 in Fig.2

and Fig.3 The structural analysis shows that all the samples are of orthorhombic symmetry This can be confirmed by the visual examination of the diffraction patterns comparing them with

reported

orthorhombic Y123 structure. The

and

refined cell

parameters and the atom positions are presented in Tables 1 . We find from this table that the lattice parameters a, and b do not change much however, c parameter is slightly affected thereby slightly affecting the O(4) parameter which is responsible for keeping the structure to be orthorhombic. With Zn substitution the parameter O(2) increases whereas parameter O(3) decreases thereby suggesting the changes in the Cu-O2 plane .It

may be noted here that this is a new series of high Tc cuprate superconductors with Pr at Y site and Zn at Cu site. Since no structural data is available , no comparison of lattice parameters and other structural parameters extracted from X-ray diffraction patterns in our study can be made with reported in literature.

Conclusion The present investigation was undertaken in order to see whether the crystal structure parameters play any role in the suppression of superconductivity in Y1-xPrxBa2 [Cu1-yZny]3O7-δ

. In particular, the attention was paid to the changes in the lattice

constants as well as the atom positions. We find that eventhough the lattice parameters there is no much change so also the other structural parameters . So the suppression of Tc may be due to some other effect like pinning the stripe phase.

y = 0.10

Intensity

0.08

0.06

0.03

0.01

0

20

30

40

50

2Θ

60

70

80

Fig. 4.3.1.

X-ray

diffraction patterns of Y1-xPrxBa2 [Cu1-yZny]3O7-δ samples with

different values of Zn concentration and x = 0.10.

Fig .2 Rietveld refined diffraction patterns of Y0.9Pr0.1Ba2 [Cu1- yZny]3O7-δ with y = 0.00

Fig .3 Rietveld refined diffraction patterns of Y0.9Pr0.1Ba2[Cu1- yZny]3O7-δ with y = 0.01

Table 1 Rietveld Refinement of XRD data for Y0.9Pr0.1Ba2[Cu1-yZny]3O7-δ . The space group is Pmmm with Y(½,½, ½) , Pr(½,½, ½), Ba (½,½, z) ,Cu(1)(0,0,0), Cu(2) (0, 0, z), O(1) (0, ½ , 0), O(2) ( ½, 0 ,z) , O(3)(0, ½, z) , O(4) (0, 0, z). Also shown oxygen content. The values in the parentheses represents uncertainity in the last digit.

z(Ba) z(Cu2)/z(Zn) z(O2) z(O3) z(O4) a(A0) b(A0) c(A0) Rwp Rexp RBragg χ 2 Oxygen

y = 0.0 y = 0.01 0.182(3) 0.182(3) 0.361(2) 0.360(2) 0.366(4) 0.367(4) 0.388(1) 0.388(1) 0.160(2) 0.163(2) 3.820(2) 3.820(2) 3.884(3) 3.884(3) 11.663(1 11.663(1) ) 16.0 14.0 12.67 1.22 6.67

15.0 12.0 12.91 1.29 6.67

y = 0.03 0.182(3) 0.361(2) 0.396(2) 0.355(4) 0.159(4) 3.823(2) 3.883(3) 11.665(1)

y = 0.06 0.182(3) 0.361(2) 0.383(2) 0.370(3) 0.159(4) 3.824(2) 3.887(1) 11.658(2)

y = 0.08 0.178(3) 0.359(2) 0.379(2) 0.336(5) 0.156(4) 3.826(2) 3.888(1) 11.668(1)

y = 0.10 0.178(3) 0.362(2) 0.378(2) 0.336(5) 0.158(4) 3.827(2) 3.889(1) 11.669(1)

12.6 13.6 11.4 1.27 6.67

15.4 13.5 9.96 1.30 6.67

15.6 14.4 16.27 1.18 6.67

15. 13.8 13.99 1.18 6.67

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