Does it really work like that? – Reproducing a paper on Na2MoO4 in a lab exercise

As part of a laboratory exercise, we are reproducing Raman measurements from the
literature. This time we chose a temperature dependent study of Na2MoO4 by Saraiva et al.
[1]. It proved to be both an interesting engineering challenge and a deep dive into old
theoretical work on Na2MoO4. The study by Saraiva et al. roughly breaks down into two parts;
the temperature dependent behavior of the cubic phase and the observation of a phase
transition from cubic (I) to orthorhombic (II). For the first part our measurements qualitatively
match the published data by Saraiva et al. (Figure (c, d)), though quantitatively, we observe a
consistent shift in one fit parameter for all bands. This might be due to two data points at ≈15
K and ≈50 K in the data set of Saraiva. It is unclear how they were measured using a
cryostat that is cooled with liquid nitrogen (≈80 K). For the phase transition we found that
there are two different
orthorhombic (II, III) phases
(Figure (b)) and that the
transition appears to be
somewhat “unstable”, which
leads us to suspect the
observation of a metastable
phase that has been descript
by Pistorius [2].
Figure: (a) Raman-measurement
setup for the insitu heating/cooling,
with improvised cooling devices, to
prevent overheating of the cell
casing. (b) Raman spectra of the
(orthorhombic) phases of Na2MoO4.
(c) Raman spectra as a function of
temperature for the main (cubic)
Na2MoO4 phase. (d) Band positions
as a function of temperature for the
spectra in (c)