Article,
Low-temperature phase transformation studies in the stearic acid: C form
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, (2015)
DOI: 10.1016/j.saa.2015.04.003
Abstract
This paper reports the temperature-dependent measurements in the C form
of stearic acid. Raman scattering, X-ray diffraction, and differential
scanning calorimetry measurements were performed at low temperatures.
The polarized Raman spectra were measured for temperatures ranging from
8 to 300 K over the spectral range of 30-3000 cm(-1). The spectral
changes observed in both the lattice vibrational modes and the internal
vibrational modes regions of the Raman spectrum, allowed to identify a
phase transition undergone by the stearic acid crystal occurring between
210 and 170 K and a change in the structure continues to be observed
down to 8 K. The anharmonicity of some vibrational modes and the
possible space groups presented by the crystal at low temperatures were
also discussed. Low-temperature X-ray diffraction measurements were
performed from 290 to 80 K and the results showed slight changes in the
lattice parameters at similar to 200 K. Furthermore, the evidence of the
phase transformation was provided by the differential scanning
calorimetry measurements, which identified an enthalpic anomaly at about
160 K. (C) 2015 Elsevier B.V. All rights reserved.
