Elucidating the phase transitions of decanoic-acid crystal by XRD, Raman, group theory and Gibbs energy analyses combined with DFT calculations.

This research reports a series of phase transitions in the decanoic-acid (DA) crystal under low-temperature conditions, which were elucidated by XRD, Raman scattering and DFT calculations in a dimer of DA in the C form (monoclinic structure). The first phase change was noticed within the 210-190 K interval duly characterized as a transition of second-order type, as indicated by Gibbs energy behavior, suggesting that the monoclinic structure (P2/c) of the crystal is not changed. The second change was observed nearly 110-90 K, whose transition is first-order type occurring from the C form to an A form (triclinic), possibly belonging to the P1 space group.