Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-Pressure Monoclinic-Monoclinic Transition in Fergusonite-type
  HoNbO4   In this paper we perform a high-pressure study of fergusonite-type HoNbO4.
Powder x-ray diffraction experiments and ab initio density-functional theory
simulations provide evidence of a phase transition at 18.9(1.1) GPa from the
monoclinic fergusonite-type structure (space group I2/a) to another monoclinic
polymorph described by space group P21/c. The phase transition is reversible
and the high-pressure structural behavior is different than the one previously
observed in related niobates. The high-pressure phase remains stable up to 29
GPa. The observed transition involves a change in the Nb coordination number
from 4 to 6, and it is driven by mechanical instabilities. We have determined
the pressure dependence of unit-cell parameters of both phases and calculated
their room-temperature equation of state. For the fergusonite-phase we have
also obtained the isothermal compressibility tensor. In addition to the
high-pressure studies, we report ambient-pressure Raman and infrared
spectroscopy measurements. We have been able to identify all the active modes
of fergusonite-type HoNbO4, which have been assigned based upon
density-functional theory calculations. These simulations also provide the
elastic constants of the different structures and the pressure dependence of
the Raman and infrared modes of the two phases of HoNbO4.

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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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The categories of this paper are: cs
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: math
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: chao-dyn