Low-temperature phase transformation studies in the stearic acid: C form

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.