title: Low-temperature phase transformation studies in the stearic acid: C form.
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.
authors.affiliation: Instituto de Ciências Exatas, Universidade Federal do Sul e Sudeste do Pará, CEP 68507-970 Marabá, PA, Brazil.
authors.forename: F F
authors.initials: FF
authors.lastname: de Sousa
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: P T C
authors.initials: PT
authors.lastname: Freire
authors.affiliation: Departamento de Física, Universidade Federal do Maranhão, 65080-040 São Luis, MA, Brazil.
authors.forename: A S
authors.initials: AS
authors.lastname: de Menezes
authors.affiliation: 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.
authors.forename: G S
authors.initials: GS
authors.lastname: Pinheiro
authors.affiliation: Institutode Física Gleb Wataghin, Universidade Estadual de Campinas, CEP 13083-859 Campinas, SP, Brazil.
authors.forename: L P
authors.initials: LP
authors.lastname: Cardoso
authors.affiliation: Faculdadede Física, Universidade Federal do Pará, CEP 66075-110 Belém, PA, Brazil.
authors.forename: P
authors.initials: P
authors.lastname: Alcantara
authors.affiliation: Faculdadede Física, Universidade Federal do Pará, CEP 66075-110 Belém, PA, Brazil.
authors.forename: S G C
authors.initials: SG
authors.lastname: Moreira
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: F E A
authors.initials: FE
authors.lastname: Melo
authors.affiliation: Departamento de Física, Universidade Federal do Ceará, CEP 60455-760 Fortaleza, CE, Brazil.
authors.forename: J
authors.initials: J
authors.lastname: Mendes Filho
authors.affiliation: Faculdadede Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará, CEP 63900-000 Quixadá, CE, Brazil. Electronic address: gilberto.saraiva@uece.br.
authors.forename: G D
authors.initials: GD
authors.lastname: Saraiva
mesh_terms: D003080:Cold Temperature; D008958:Models, Molecular; D044367:Phase Transition; D033362:Powder Diffraction; D013059:Spectrum Analysis, Raman; D013229:Stearic Acids / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D013229:Stearic Acids; C031183:stearic acid
keywords: Polarized Raman scattering; Stearic acid crystals; Structural changes; X-ray powder diffraction