Mechanically activated MoO3 has been characterized by infrared and Ram
an spectroscopy. A drastic decrease in the Raman intensity connected w
ith particle size reduction is observed when MoO3 is ground in a plane
tary mill for 600 min. The broadening of Raman bands is linearly corre
lated with the increasing BET surface area. The observed changes in Ra
man intensity ratios are related to the known lattice contraction and
expansion of MoO3-x and thus arise from known distortions in suboxides
. Mechanical activation induces only minor internal. lattice strain; t
hus, only small shifts of the bands assigned to rigid chain modes are
observed. New small bands observed below 50 cm(-1) are attributed to b
ackfolded phonon modes due to the formation of shear superstructures,
which were detected by XRD and HRTEM. A resonance effect is indicated
by a shift of these bands upon changing the excitation wavelength from
457.9 to 487.9 and 514.5 nm, respectively. This resonance effect is c
onfirmed using a laser line at 621.9 nm, which results in a much broad
er Rayleigh wing, and a multitude of bands below 116 cm(-1), a reverse
d intensity of the pair of wagging modes at 283/290 cm(-1), and additi
onal shoulders at 621, 639, 990, and 1005 cm(-1). Further confirmation
is found in a resonance Raman experiment, where the bands observed ar
e suggested to arise from Mo5+=O stretching vibrations of defect sites
, which were also detected by DR-UV/vis and ESR spectroscopies. The tr
ansmission IR spectra in the far-infrared region (200-35 cm(-1)) are a
ffected in a complex way by particle size reduction and the increasing
influence of grain surfaces. This behavior of the FIR bands is connec
ted with the complex, stepwise particle size reduction revealed by XRD
. The observed spectral changes in the far-infrared (450-200 cm(-1)) a
nd mid-infrared (1200-450 cm(-1)) regions as compared to single-crysta
l data, are explained by TO-LO splitting of the B-3u, modes. DRIFTS is
found to be more sensitive toward spectral changes due to LO-TO split
ting and toward minority species, like molybdenum hydrates, as compare
d td transmission IR spectroscopy, probably due to the higher surface
sensitivity of this technique. Combination modes above 1010 cm(-1) los
e intensity upon particle size reduction, thus reflecting the destruct
ion of the MoO3 lattice. A drastic increase in the intensity of bands
that are assigned to OH vibrations indicates the presence of water int
erconnected by H bonds in microcrystalline MoO3. The detection of the
OHO deformation mode at 1425 cm(-1) and additional signals at 770 and
955 cm(-1) reveals an increasing formation of molybdenum hydrates upon
mechanical activation.