NMR · NQR and DTA · DSC Studies of Phase Transitions in Pyridinium Tetrachloropalladate(II) and Pyridinium Tetrachloroplatinate(II)

1998 ◽  
Vol 53 (6-7) ◽  
pp. 419-426 ◽  
Author(s):  
Tetsuo Asaji ◽  
Keizo Horiuchi ◽  
Takehiko Chiba ◽  
Takashige Shimizu ◽  
Ryuichi Ikeda
Keyword(s):  
Phase Transitions ◽  
Low Temperatures ◽  
Structural Phase ◽  
Orientational Order ◽  
Second Order ◽  
Order Transition ◽  
Spin Lattice Relaxation ◽  
Potential Wells ◽  
H Nmr ◽  
Second Order Transition

Abstract From the measurements of DTA • DSC and the temperature dependences of 35Cl NQR frequencies, phase transitions were detected at 150 K, 168 K, and 172 K for (pyH)2 [PtCl4], and at 241 K for (PyH)2 [PdCl4]. In order to elucidate the motional state of the constituent ions in the crystals in connection with the structural phase transitions, the 35Cl NQR and 1H NMR spin-lattice relaxation times and the second moment of the 1H NMR line were measured as functions of temperature. For both compounds, the potential wells for the cationic reorientation are suggested to be highly nonequivalent at low temperatures. Above 168 K, the pyridinium ions in (pyH)2[PtCl4] are expected to reorient between almost equivalent potential wells. As for (pyH)2[PdCl4], it is expected that the orientational order of the cation still remains even above the second order transition at 241 K. A change of the potential curve from two-unequal to three-unequal wells is proposed as a possible mechanism of the second order transition. The activation energies for the cationic motion in the respective model potential are derived for both compounds at high and low temperatures.

Structural Phase Transitions and Ionic Motions in Pyridinium Hexachlorotellurate(IV),Hexachlorostannate(IV), and Hexabromostannate(IV) Crystals as Studied by 1H NMR

1989 ◽  
Vol 44 (4) ◽  
pp. 300-306 ◽  
Author(s):  
Yutaka Tai ◽  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Scanning Calorimetry ◽  
Spin Lattice ◽  
H Nmr

Abstract The 1H NMR second moment M2 and the spin-lattice relaxation time T1 are determined for pyridinium hexachlorotellurate(IV), hexachlorostannate(IV), and hexabromostannate(IV) at various temperatures above ca. 140 K. The phase transition temperatures already reported from halogen NQR experiments are determined as 272, 331, and 285 K, respectively, by differential thermal analysis (DTA). The DTA as well as differential scanning calorimetry measurements show that the above phase transitions are of second-order. For pyridinium hexachlorotellurate(IV) and hexa-bromostannate(I V), a sharp 1H T1 dip was observed at the transition temperature. This is interpreted in terms of a phenomenon related to the critical fluctuation of an order parameter. From the measurements of 1H M2, 60° two-site jumps (60° flips) around the pseudo C6 axis of the cation are suggested to occur in the high temperature phases of the complexes. Modulation of X...1H (X = CI, Br) magnetic dipolar interactions due to the reorientational motion of the complex anions is considered as a possible relaxation mechanism in the high temperature phases.

Structural Phase Transitions and Cationic Motions in Pvridinium Dichloroiodate(I) as Studied by 1H NMR, Differential Thermal Analysis, and Powder X-Ray Diffraction

1989 ◽  
Vol 44 (11) ◽  
pp. 1111-1115 ◽  
Author(s):  
Reiko Watanabe ◽  
Tetsuo Asaji ◽  
Yoshihiro Furukawa ◽  
Daiyu Nakamura ◽  
Ryuichi Ikeda
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Phase Transitions ◽  
Room Temperature ◽  
Structural Phase ◽  
Spin Lattice Relaxation ◽  
Growth Time ◽  
Stable Phase ◽  
Temperature Phase ◽  
H Nmr

For crystals of pyridinium dichloroiodate (I), (pyH)ICl2, the temperature dependences of the 1H NMR spin-lattice relaxation time T1 and the 1H second moment M2 were determined. M2 was found to be small (~ 1 G2) above room temperature, indicating that the cations perform rapid reorientational motion about their pseudohexad axis perpendicular to the cationic plane. 1H T1 at its minimum was unusually long, indicating this motion occurring in the low symmetry local environments. Phase transitions between stable solid phases were revealed at 282 and 373 K by the 1H NMR measurements and differential thermal analysis. The highest-temperature phase was easily supercooled and transformed reversibly into another metastable phase and back on cooling and warming at almost the same temperature of 138 K. The kinetics of the phase transition from the supercooled to the stable phase at room temperature was analyzed using an Avrami type relation. The growth time of the stable phase was estimated to be about 14 h at room temperature

2H NMR Study on Phase Transitions and Crystal Dynamics of p-Chloro- and p-Bromobenzyl Alcohols

2002 ◽  
Vol 57 (6-7) ◽  
pp. 388-394 ◽  
Author(s):  
Motohiro Mizuno ◽  
Masanori Hamada ◽  
Tomonori Ida ◽  
Masahiko Suhara ◽  
Masao Hashimoto
Keyword(s):  
Relaxation Time ◽  
Phase Transitions ◽  
Nmr Spectra ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Hydrogen Atoms ◽  
Potential Wells ◽  
H Nmr ◽  
Nmr Study ◽  
Crystal Dynamics

Two phase transitions of 4-chlorobenzyl alcohol (pCBA) and 4-bromobenzyl alcohol (pBBA), from the low-temperature phase (LTP) to the intermediate-temperature phase (ITP) and from ITP to the room-temperature phase (RTP), were investigated by 2H NMR and differential scanning calorimetry (DSC). The crystal dynamics in each phase were studied using the 2H NMR spectra, the spin-lattice relaxation time (T1) and the relaxation time of quadrupole order (T1Q) for the samples, where the hydrogen of the -OH group was selectively deutrated. The 2H NMR 1 of both crystals in the RTP were dominated by the fluctuation of the electric field gradient at 2H nucleus caused by vibrational motions of the -CH2OH group. In the LTP of both crystals, the fast jump of hydrogen atoms between the two sites corresponding approximately to the positions of the hydroxyl hydrogen atoms in the RTP and LTP were found from 2H NMR spectra. The results of T1 and T1Q in the LTP revealed that the jump of hydrogen atoms occurs in asymmetric potential wells and that these potential wells gradually approach symmetric ones with increasing temperature on the high-temperature side in the LTP

Crystallization and Second-Order Transitions in Silicone Rubbers

1951 ◽  
Vol 24 (2) ◽  
pp. 366-373 ◽  
Author(s):  
C. E. Weir ◽  
W. H. Leser ◽  
L. A. Wood
Keyword(s):  
Thermal Expansion ◽  
Volume Change ◽  
Silicone Rubber ◽  
Low Temperatures ◽  
Linear Thermal Expansion ◽  
Second Order ◽  
Order Transition ◽  
General Electric ◽  
Second Order Transition ◽  
Silicone Rubbers

Abstract In the course of an investigation to determine which rubbers might be suitable for use at low temperatures, interferometric measurements of the length-temperature relationships of silicone rubbers have been made. Crystallization was found between −60° and −67° C in Dow-Corning Silastic X-6160 and in General Electric 9979G silicone rubber, the latter of which contains no filler. Crystallization between −75° and −85° C was found in Silastic 250. Melting occurred over a range of temperature above the temperature of crystallization. The volume change on crystallization varied from 2.0 to 7.8 per cent. No crystallization or melting phenomena were observed in Silastic X-6073 between −180° and +100° C. All types of silicone rubber exhibited a second-order transition at about −123° C, the lowest temperature at which such a transition has been observed in a polymer. The coefficient of linear thermal expansion of silicone rubbers containing no filler was found to be about 40×10−5/degree C between −35° and 0° C.

Beta Ray Absorption in Polymers and Determination of First and Second-Order Transition Temperatures

1963 ◽  
Vol 36 (2) ◽  
pp. 459-472 ◽  
Author(s):  
R. Zannetti ◽  
P. Manaresi ◽  
L. Baldi
Keyword(s):  
Phase Transitions ◽  
Natural Rubber ◽  
Good Accuracy ◽  
Second Order ◽  
Order Transition ◽  
Beta Radiation ◽  
Transition Temperatures ◽  
Inorganic Substances ◽  
Second Order Transition

Abstract It is possible to determine the first- and second-order transition temperatures of polymers, copolymers, and other organic and inorganic substances with good accuracy and reproducibility by measuring their absorption of beta radiation. Variations in the measured absorptions are in essence related to variations in the product of the density and thickness of the sample, so that the method can be employed, in practice, when seeking information concerning variations in density, with the temperature or the time. The technique was used to investigate a number of polymers, e.g., polyethylene terephthalate, polystyrene, polyethylene, 1,4-cis polybutadiene, natural rubber, polyisobutylene, polybutene-1, polypropylene, and certain copolymers of ethylene/propylene and ethylene/butene-1. Finally, data pertaining to phase transitions in organic and inorganic substances are presented. The results are discussed., and compared with those obtained by other methods.

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