Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Melting of the Na layers in solid Na0.8CoO2   Data of 23Na NMR spectra- and relaxation measurements are interpreted as
suggesting that, upon increasing temperature the Na layers in Na0.8CoO2 adopt a
2D liquid state at T=291 K. The corresponding first order phase transition is
preceded by a rapidly increasing mobility and diffusion of Na ions above 200K.
Above 291 K the 23Na NMR response is similar to that previously observed in
superionic conductors with planar Na layers.

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The categories of this paper are: astro-ph
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin