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High-entropy oxides (HEOs) comprise an equimolar mixing of metal cations
combined into a single-phase crystal structure. First synthesized in 2015 [1],
HEOs have garnered much attention as candidates for high-efficiency batteries
and heat shields [2, 3]. HEOs composed of four and five binary oxides have
been previously investigated by infrared [4] and Raman spectroscopy [5] and
lattice dynamical simulations. The IR spectra consist of a strong, reststrahlen
mode at $350~\textrm{cm}^{-1}$ and a much weaker mode at $150~\textrm{cm}^{-1}$ not predicted by
group theory. The absence of spin-phonon splitting in the reststrahlen band
below the Neel temperature ($T_N$), despite appearing in the parent oxides CoO
and NiO, has been attributed to a high rate of static disorder scattering. The
Raman spectra are composed of five peaks which have been assigned to $TO, LO,
LO+TO, 2LO$ modes, as well as a two-magnon mode. Fits of the spectra to the
Lorentz oscillator model revealed a temperature-dependent damping parameter
which was ascribed to anharmonic effects. The phonon density of states will be
simulated using GULP [6] in order to understand the IR and Raman spectra.
[1] Christina Rost et al. “Entropy-stabilized oxides”. In: Nature Communica-
tions 6 (Sept. 2015), p. 8485. doi: 10.1038/ncomms9485.
[2] Abhishek Sarkar et al. “High Entropy Oxides for Reversible Energy Stor-
age”. In: Nature Communications 9 (Aug. 2018). doi: 10.1038/s41467-
018-05774-5.
[3] Joshua Gild et al. “High-entropy fluorite oxides”. In: Journal of the Euro-
pean Ceramic Society 38.10 (2018), pp. 3578–3584. issn: 0955-2219. doi:
https://doi.org/10.1016/j.jeurceramsoc.2018.04.010. url: https:
//www.sciencedirect.com/science/article/pii/S0955221918302115.
[4] Tahereh Afsharvosoughi and D. A. Crandles. “An infrared study of antifer-
romagnetic medium and high entropy rocksalt structure oxides”. In: Jour-
nal of Applied Physics 130.18 (2021), p. 184103. doi: 10.1063/5.0070994.
eprint: https://doi.org/10.1063/5.0070994. url: https://doi.org/
10.1063/5.0070994.
[5] Tahereh Afsharvosoughi. “Structural, Magnetic and Vibrational Studies of
Entropy Stabilized Oxides”. Brock University, 2021.
[6] Julian D. Gale. “GULP: A computer program for the symmetry-adapted
simulation of solids”. In: J. Chem. Soc., Faraday Trans. 93 (4 1997), pp. 629–
637. doi: 10 . 1039 / A606455H. url: http : / / dx . doi . org / 10 . 1039 /
A606455H.
