Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High Pressure X-ray Diffraction Study of MgMn2O4 Tetragonal Spinel   The phase stability of the MgMn2O4 spinel has been studied by means of
high-pressure X-ray diffraction for pressures up to 30 GPa. Two samples with
different inversion degrees have been considered. Both spinels undergo a phase
transition towards an orthorhombic structure (CaMn2O4-type). For the more
inverted sample the transition pressure is at least 1 GPa lower with respect to
that of the less inverted spinel. Also the volume contraction, relative
compressibility and density trends are different for the two samples. These
variations have been explained according to differences in the cation
distribution. and electronic properties of the samples.

12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph
35
The categories of this paper are: mtrl-th