Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Structural phase transition and its consequences on optical behavior of
  LaV$_{1-x}$Nb$_x$O$_4$   We present the structural, electronic, vibrational, and photoluminescence
properties of polycrystalline LaV$_{1-x}$Nb$_x$O$_4$ ($x =$ 0--0.2) samples at
room temperature. The substitution of Nb at the V site shows the fascinating
structural and optical behavior due to their isoelectronic character and larger
ionic radii of Nb$^{5+}$ as compared to the V$^{5+}$. The Rietveld refinement
of x-ray diffraction patterns demonstrate that the $x=$ 0 sample exist in a
monoclinic (P2$_1$/n) phase, whereas for the $x >$ 0, both monoclinic and
scheelite-tetragonal (I4$_1$/a) phases co-exist in a certain proportion.
Interestingly, a monotonous enhancement in the Raman spectral intensity with Nb
substitution is correlated with the substitution induced increase in the
scheelite-tetragonal phase. The x-ray absorption measurements reveal that the
La ions exist in a trivalent oxidation state, while V and Nb cations possess 5+
oxidation state in tetrahedral coordination. Moreover, the Fourier-transform
infrared (FTIR) spectra indicate that the Nb substitution give origin to some
additional IR modes owing to the deformation of the VO$_4$$^{3-}$ tetrahedra
and mixing of monoclinic and tetragonal phases. The photoluminescence
measurements on these samples exhibit broadband spectra and their deconvolution
designate the availability of more than one electron-hole pairs recombination
center.

29
The categories of this paper are: funct-an
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
37
The categories of this paper are: supr-con
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom