Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Local Disorder in the Oxygen Environment Around Praseodymium in YBCO:Pr
  from X-ray Absorption Fine Structure   We present K-edge XAFS (X-Ray Absorption Fine Structure) data for various
concentrations of Pr in Y$_{1- x}$Pr$_{x}$Ba$_{2}$Cu$_{3}$O$_{7}$. The
character of the Pr K-edge XAFS data indicate that most of the Pr substitutes
onto the Y site and is well ordered with respect to the unit cell. These data
also show that the amplitude of the first Pr-O peak is greatly reduced when
compared to the first Y-O peak in pure YBCO, and decreases with increasing Pr
concentration. In contrast, the Y K-edge data for these alloys show little if
any change in the oxygen environment, while the Cu K-edge data show a 10\%
reduction in the first Cu-O peak. Fits to the Pr data suggest that some oxygen
atoms about the Pr become disordered and/or distorted; most of the Pr-O
nearest- neighbor distances are 2.45 \AA, but about 15-40\% of them are in a
possibly broadened peak at 2.27$^{+0.03}_{-0.12}$ \AA. The Cu K-edge XAFS data
show a slight broadening but no loss of oxygens, which is consistent with a
radial distortion of the Pr-O bond. The existence and the size of these two
bond lengths is consistent with a mixture of Pr$^{3+}$ and Pr$^{4+}$ bonds, and
to a formal valence of +3.33$^{+0.07}_{-0.18}$ for the Pr ion. This paper
should be published in Feb. 1994 in Phys. Rev. B.

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The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
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The categories of this paper are: astro-ph
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
3
The categories of this paper are: physics
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th