Nuclear quadrupole resonance study of phase transition in tetrachloro‐p ‐benzoquinone (chloranil)
15 Nov 1973-Journal of Chemical Physics (American Institute of Physics)-Vol. 59, Iss: 10, pp 5392-5396
TL;DR: In this paper, the phase transition in chloranil crystal has been studied by measurements of the 35Cl nuclear quadrupole resonance frequency and the spin-lattice relaxation time.
Abstract: The phase transition in chloranil crystal has been studied by measurements of the 35Cl nuclear quadrupole resonance frequency and the spin‐lattice relaxation time. The splitting of the resonance line in the low temperature phase was shown to behave as an order parameter of the phase transition. The experimental order parameter and the anomalous behavior of the transition probability (1/T1) near the transition point were interpreted satisfactorily in terms of the librational soft‐mode theory which assumes anharmonic coupling between molecular librational modes in the crystal.
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TL;DR: The anomalous heat capacity of solid chloranil was measured between 11 and 300 °K with particular attention to the phase transition at 92 °K, where the heat and entropy of the transition were 38 J mol−1 and 0.41 J °K−1 ·mol−1, respectively.
Abstract: Molar heat capacity of solid chloranil was measured between 11 and 300 °K with particular attention to the phase transition at 92 °K. The heat and entropy of the transition were 38 J mol−1 and 0.41 J °K−1 · mol−1. The transition is of a lambda shape starting at 70 °K and ends at 100 °K. The anomalous heat capacity curve was explained by the soft librational mode theory. There is another large transition at about 570 °K. The shape and magnitude of the transitions are very sensitive to the long‐range regularity of the structure and depend on the method of preparation.
37 citations
TL;DR: In this paper, the authors performed heat capacity measurements on 1-1′-biphenyl and revealed two broad anomalies at 11.0 K and 40.4 K, respectively.
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31 citations
TL;DR: In this article, the second order phase transition from hexagonal to monoclinic was studied in detail, and the splittings of the NQR lines in the monOClinic phase, which are proportional to the order parameter, were found to vanish with the critical exponent β = 1/2 on approaching Tc.
Abstract: 14N NQR frequencies, linewidth, and spin–lattice relaxation times were measured in s‐triazine as a function of temperature between 77 and 280 °K. The second order phase transition from hexagonal to monoclinic which takes place at the critical temperature Tc=198.8 °K was studied in detail. The splittings of the NQR lines in the monoclinic phase, which are proportional to the order parameter, were found to vanish with the critical exponent β=1/2 on approaching Tc. Above 210 °K the temperature dependence of the linewidth and of the spin–lattice relaxation time indicates that the s‐triazine molecule undergoes molecular reorientation around its threefold axis. The activation enthalpy for this motion was found to be ΔH=14.0 kcal/mole. These relaxation phenomena were analyzed using a density matrix formalism. Explicit expressions for the decay exponents and signal function were derived.
24 citations
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TL;DR: In this article, the linear response of a given system to an external perturbation is expressed in terms of fluctuation properties of the system in thermal equilibrium, which may be represented by a stochastic equation describing the fluctuation, which is a generalization of the familiar Langevin equation in the classical theory of Brownian motion.
Abstract: The linear response theory has given a general proof of the fluctuation-dissipation theorem which states that the linear response of a given system to an external perturbation is expressed in terms of fluctuation properties of the system in thermal equilibrium. This theorem may be represented by a stochastic equation describing the fluctuation, which is a generalization of the familiar Langevin equation in the classical theory of Brownian motion. In this generalized equation the friction force becomes retarded or frequency-dependent and the random force is no more white. They are related to each other by a generalized Nyquist theorem which is in fact another expression of the fluctuation-dissipation theorem. This point of view can be applied to a wide class of irreversible process including collective modes in many-particle systems as has already been shown by Mori. As an illustrative example, the density response problem is briefly discussed.
4,096 citations
TL;DR: In this paper, the authors compared theory and experiment for behavior very near critical points, and suggested that scaling laws provide a promising approach to understand phenomena near the critical point, but that they are by no means proved or disproved by the existing experimental data.
Abstract: This paper compares theory and experiment for behavior very near critical points. The primary experimental results are the "critical indices" which describe singularities in various thermodynamic derivatives and correlation functions. These indices are tabulated and compared with theory. The basic theoretical ideas are introduced via the molecular field approach, which brings in the concept of an order parameter and suggests that there are close relations among different phase transition problems. Although this theory is qualitatively correct it is quantitatively wrong, it predicts the wrong values of the critical indices. Another theoretical approach, the "scaling law" concept, which predicts relations among these indices, is described. The experimental evidence for and against the scaling laws is assessed. It is suggested that the scaling laws provide a promising approach to understanding phenomena near the critical point, but that they are by no means proved or disproved by the existing experimental data.
1,189 citations
TL;DR: In this paper, the electron spin resonance of F 3+ in single crystals of SrTiO 3 has been studied in the low temperature phase below 110°K, and the resonance lines exhibited small splitting in addition to the usual tetragonal splitting.
Abstract: The electron spin resonance of F 3+ in single crystals of SrTiO 3 has been studied in the low temperature phase below 110°K. The resonance lines exhibited small splitting in addition to the usual tetragonal splitting. The orientation dependence of the splitting was measured at 77°K and at 4.2°K. The whole spectrum is explained to be due to the rotation of oxygen octahedron in the (100) plane, the angle of rotation being 1.4° at 77°K and 2.1° at 4.2°K. Corresponding splitting was also observed for the case of the `strong axial field' spectrum due to Fe 3+ accompanied by the nearest neighbor oxygen vacancy. The observed angles of rotation are about 30 percent smaller than those of the former case. The crystal structure deduced from the atomic positions of oxygen ions will be D 4 h 16 in the low temperature phase. Correlation with the resonance data of Gd 3+ in SrTiO 3 is discussed.
330 citations
TL;DR: In this article, Debye, P. VAN PANTHALEON VAN ECK, C. Z. MEI~KE, H. MENDEL, and H. H.MENDEL (1962b). Acta Cryst. 15, 113.
Abstract: DEBYE, P. (1927). Phys. Z. 28, 135. KROGH-MOE, J. (1956). Acta Cryst. 9, 951. ME~KE, H. (1932). Phys. Z. 33, 593. MEI~)ET,, I-I. (1962a). Acta Cryst. 15, 113. MENDEL, i . (1962b). Acta Cryst. 15, 9. NO~MAN, :N. (1957). Acta Cryst. 10, 370. VAN PANTHALEON VAN ECK, C. L., MENDEL, H. • BOOG, W. (1957). Disc. Faraday Soc. 24, 200. VAN PANTHALEON VAN ECK, C. L., MENDEL, H. & FA~RENFORT, J. (1958). Prec. Roy. Soc. (London), A, 247, 472. ZER~KE, F. & PRn~S, J. A. (1927). Phys. Z. 41, 184.
89 citations
TL;DR: The magic echoes described by Waugh are shown to have a number of useful applications in the nuclear magnetic resonance of solids, such as lineshape analysis of free induction decays and high-resolution NMR in solids as discussed by the authors.
40 citations