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Spectrochim Acta A Mol Biomol Spectrosc. 2015 Sep 5;148:280-8. doi: 10.1016/j.saa.2015.04.003. Epub 2015 Apr 8.

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

Author information

1
Instituto de Ciências Exatas, Universidade Federal do Sul e Sudeste do Pará, CEP 68507-970 Marabá, PA, Brazil.
2
Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil.
3
Departamento de Física, Universidade Federal do Maranhão, 65080-040 São Luis, MA, Brazil.
4
Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil; Departamento de Física, Campus Ministro Petrônio Portella, Universidade Federal do Piauí, CEP 64049-550 Teresina, PI, Brazil.
5
Institutode Física Gleb Wataghin, Universidade Estadual de Campinas, CEP 13083-859 Campinas, SP, Brazil.
6
Faculdadede Física, Universidade Federal do Pará, CEP 66075-110 Belém, PA, Brazil.
7
Faculdadede Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará, CEP 63900-000 Quixadá, CE, Brazil. Electronic address: gilberto.saraiva@uece.br.

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 ∼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.

KEYWORDS:

Polarized Raman scattering; Stearic acid crystals; Structural changes; X-ray powder diffraction

PMID:
25909902
DOI:
10.1016/j.saa.2015.04.003
[Indexed for MEDLINE]

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