<sup>35</sup>Cl nuclear quadrupole resonance study of the structural phase transition in 1,2,4,5-tetrachlorobenzene
C A Martin; C A Martin; Fac. de Matematica, Astron. y Fisica, Univ. Nacional de Cordoba, Argentina
Журнал:
Journal of Physics: Condensed Matter
Дата:
1992-02-17
Аннотация:
The crystallographic phase transition which 1,2,4,5-tetrachlorobenzene undergoes at about 188 K from a high-temperature monoclinic (P2<sub>1</sub>/a) structure to a low-temperature triclinic (P1) structure has been studied by means of the <sup>35</sup>Cl nuclear quadrupole resonance transition frequencies measured as a function of temperature from 77 to 300 K. The transition is shown to be first order displacive, determining the order parameter and its temperature dependence, and deducing a critical exponent beta =0.309+or-0.012 which indicates that the system behaves as a 3D Ising-like model where the important forces are those of short range. Also, the measured spectra are shown to be consistent with the measured (P2<sub>1</sub>/a) and proposed (P1) crystal structures, producing an assignment of the spectra to the various chlorine sites in both primitive unit cells. Additionally, a wide temperature range (approximately 165-205 K) where phases coexist in a stable form is found and analysed.
320.7Кб