Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-pressure structural, elastic, and thermodynamic properties of
  zircon-type HoPO4 and TmPO4   Zircon-type HoPO4 and TmPO4 have been studied by single-crystal x-ray
diffraction and ab initio calculations. We report information on the influence
of pressure on the crystal structure, and on the elastic and thermodynamic
properties. The equation of state for both compounds is accurately determined.
We have also obtained information on the polyhedral compressibility which is
used to explain the anisotropic axial compressibility and the bulk
compressibility. Both compounds are ductile and more resistive to volume
compression than to shear deformation at all pressures. Furthermore, the
elastic anisotropy is enhanced upon compression. Finally, the calculations
indicate that the possible causes that make unstable the zircon structure are
mechanical instabilities and the softening of a silent B1u mode.

37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
35
The categories of this paper are: mtrl-th
30
The categories of this paper are: q-alg