The incommensurate phase of 4,4'-dichlorobiphenyl sulphone reinvestigated by³⁵Cl NQR

Abstract

In order Lo acquire new informntion about the normal-incommensurate (IC) phase transition and to check the existence of a lock-in transition in 4,4'-dichlombiphenyl sulphone (4.4'-0Css), a comprehensive "Cl nuclear quadrupole resonance (NQR) study is reported.Detailed NOR mwurements of frequency, line width and spin relaxation time ( T I ) were obtained in the temperature range 80-270 K. The results show that the IC phose is present from 1.50 K down to 80 K. The behaviour of the NQR spectrum in the trmsition region suggests that the IC modulation IS dominated by the first-order term in the order panmeter. The tt values at the p e L s of the IC specmm are quite different, suggesting strong onharmonic effects. No lock-in rrmsition was detected at 115 K. Small changer in the temperature behaviour of the frequency and the tl of the low-frequency IC peak were observed from temperatures lower than 110 K. Neither impurities nor thermal hysteresis effects were detected.

Finite-size effects on the incommensurate phase transition of bis(4-chlorophenyl)sulphone studied byCl35NQR

“…The NQR spectrum is composed of a single inhomogeneously broadened resonance line. The second moment of this electric-field gradient ͑EFG͒ distribution is one order of magnitude greater than that observed in bulk, 21 possibly due to a distribution of film thickness values and different orientations of the film crystalline axis with respect to the substrate. In order to study the temperature behavior of the NQR frequencies, only the first moment of the EFG distribution will be regarded.…”

“…1 and 2, a continuous splitting of the NQR line can be observed for temperatures below 156 K. This behavior of the NQR spectra of the BCPS film indicates a continuous structural phase transition as in the bulk sample. 21 Nevertheless, the transition temperature is shifted 6°above that observed in bulk. Thermal hysteresis effects were not detected in the transition temperature or in the spectral features.…”

“…For a comparison, NQR frequencies of the bulk sample are superimposed. 21 From Figs. 1 and 2, a continuous splitting of the NQR line can be observed for temperatures below 156 K. This behavior of the NQR spectra of the BCPS film indicates a continuous structural phase transition as in the bulk sample.…”

“…This compound has been extensively characterized by x-ray diffraction, 12,15 Raman spectroscopy, 16 calorimetric measurements, 17 neutron scattering, 18 NMR, 19 and NQR. 20,21 Thus, BCPS is a suitable compound to carry out a comparative study between film and bulk behavior of the IC phase.…”

35Cl Nuclear Magnetic Resonance Study in Bis(4-Chlorophenyl)Sulphone [(ClC6H4)2SO2]

“…Some of them were limited to the study of the spin-lattice relaxation time [5][6][7] and phase transitions [7,8]. The variation of the 35 Cl spin-lattice relaxation rate over the incommensurate NQR frequency distribution in BCPS has been measured at various temperatures by Schneider et al [9], Pusiol et al [6], Blinc et al [5], and Decker and Petersson [7]. The characteristic features of the variation of the effective spin-lattice relaxation rate T --1 over the incommensurate NQR frequency distribution were explained in terms of competing phason and amplitudon contributions.…”