X-ray Study on Structural Phase Transition of 4,4''-Difluoro-p-terphenyl and 4,4'''-Difluoro-p-quaterphenyl

Low-temperature X-ray diffraction experiments were performed on 4,4''-difluoro-p-terphenyl (DFTP) and 4,4'''-Difluoro-p-quaterphenyl (DFQP). The structure analyses were performed for the high-temperature phases and the librational motion of the benzene rings was analyzed. The super-lattice reflections were found in DFQP below about 200 K on the same position as the low-temperature phase of p-quaterphenyl. In DFTP, the satellite reflections with small wavevector component d_c (about 1/6) along the c*-axis were found below the transition temperature.
(Solid State Commun., 91, 89-92 (1994))

Incommensurate Crystal-Instability and a Role of Internal Degrees of Freedom in Bis(4-chlorophenyl)sulfone Molecules

Phonon dispersion relations of crystalline bis(4-chlorophenyl)sulfone were calculated assumind various degree of flexibility of the molecule. A dip in the lowest branch appeared around the location of the satellite reflection observed experimentally in the incommensurate phase, irrespective of the flexibility. An internal degree of freedom of the molecule, which breaks the two-fold axis of the molecule, couples with the lowest branch and strongly enhances the dip.
(Solid State Commun., 81, 241-243 (1992))

See also Displacive Transition or Order-Disorder Transition?

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