Differential Thermal Analysis and Dielectric Studies on 2-Methyl-2-Nitro-Propane under High Pressure

1995 ◽  
Vol 50 (4-5) ◽  
pp. 502-504 ◽  
Author(s):  
D. Büsing ◽  
M. Jenau ◽  
J. Reuter ◽  
A. Würflinger ◽  
J. Li. Tamarit
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Temperature Phase ◽  
Dielectric Studies ◽  
Static Permittivity ◽  
Coexistence Region ◽  
Disordered Phase ◽  
Plastic Phase ◽  
Related Compounds ◽  
Low Temperature Phase

Abstract Differential thermal analysis and dielectric studies under pressures up to 300 MPa and temperatures of about 200 to 350 K have been performed on 2-methyl-2-nitro-propane (TBN). TBN displays an orientationally disordered phase (ODIC), solid I, and two non-plastic phases, solids II and III. The coexistence region of the plastic phase I increases with increasing pressure, whereas the low-temperature phase II apparently vanishes at a triple point I, II, III, above 300 MPa. The static permittivity increases on freezing, characterizing the solid I as an ODIC phase. In the frame of the Kirkwood-Onsager-Fröhlich theory the g-factor is about unity, discounting specific dielectric correlations. The dielectric behaviour of TBN is similar to previously studied related compounds, such as 2-chloro-2-methyl-propane or 2-brome- 2-methyl-propane

Differential Thermal Analysis and Dielectric Studies on Neopentanol under Pressure

1992 ◽  
Vol 47 (11) ◽  
pp. 1127-1134 ◽  
Author(s):  
H. G. Kreul ◽  
R. Waldinger ◽  
A. Würflinger
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Relaxation Time ◽  
Phase Transitions ◽  
Dielectric Relaxation ◽  
Pressure Dependence ◽  
Dielectric Relaxation Time ◽  
Dielectric Studies ◽  
Dielectric Measurements ◽  
Plastic Phase

Abstract Differential thermal analysis (DTA) and dielectric measurements have been performed on 2,2-dimethyl- 1-propanol (neopentanol) up to 200 MPa. Neopentanol exhibits at least one orientationally disordered (ODIC) phase (solid I) that transforms at lower temperatures to a non-plastic phase (solid II). There is evidence of a further ODIC phase denoted as solid I'. The pressure dependence of the phase transitions and the dielectric behaviour up to frequencies of 13 MHz are described. Activation enthalpies and volumes are derived from the dielectric relaxation time and compared with results for other alcohols

Structural phase transition to disorder low-temperature phase in [Fe(ptz)6](BF4)2 spin-crossover compounds

2012 ◽  
Vol 68 (1) ◽  
pp. 40-56 ◽  
Author(s):  
Joachim Kusz ◽  
Maciej Zubko ◽  
Reinhard B. Neder ◽  
Phillipp Gütlich
Keyword(s):  
Short Range ◽  
Short Range Order ◽  
Spin Crossover ◽  
Structural Phase ◽  
The Other ◽  
Special Technique ◽  
Temperature Phase ◽  
Disordered Phase ◽  
Novel Approach ◽  
Low Temperature Phase

In the spin-crossover compound [Fe(ptz)6](BF4)2 (where ptz=1-n-propyltetrazole) six different phases are observed. When a single crystal is slowly cooled from high temperatures to those below 125 K, the reflections broaden into diffuse maxima and split into two maxima along the c* direction [Kusz, Gütlich & Spiering (2004). Top. Curr. Chem. 234, 129–153]. As both maxima are broad along the c* direction, the short-range order exists only along the c direction and in the ab plane the structure remains long-range ordered. In this disordered phase additional satellite reflections appear. Upon heating above 135 K, the diffuse maxima return to their previous shape and this process is completely reversible. Rapidly cooled samples, on the other hand, do not show such splitting and the symmetry remains R\bar 3, despite a jump in lattice parameters. We use a special technique to analyse the disorder model of the slowly cooled samples, which consists of layered domains shifted in the hexagonal ab plane. The low-spin disordered phase was solved in a novel approach to accommodate the very unusual twinning and refined in the non-standard space group C\bar 1. In contrast to the ordered low-spin phase, the Fe ion is in a non-centrosymmetric coordination polyhedron and two of the six propyl groups change their conformation.

scholarly journals High-Temperature Superconductors and Related Compounds Studied by Mössbauer Spectroscopy

1993 ◽  
Vol 15 (3-4) ◽  
pp. 211-224 ◽  
Author(s):  
E. Kuzmann ◽  
Z. Homonnay ◽  
S. Nagy ◽  
M. Gál ◽  
A. Vértes
Keyword(s):  
Phase Transformation ◽  
Mössbauer Spectroscopy ◽  
High Temperature ◽  
Low Temperature ◽  
Mossbauer Spectroscopy ◽  
High Temperature Superconductors ◽  
Temperature Phase ◽  
Mößbauer Spectroscopy ◽  
Related Compounds ◽  
Low Temperature Phase

57Fe,119Sn, and151Eu Mössbauer spectroscopy was used to study the chemical structure, phonon mode changes, and low-temperature phase transformation around the Tcas well as suppression of superconductivity in high-temperature superconductors and related compounds. Anomalous temperature-dependent changes in the total57Fe spectral area fraction and in the Mössbauer line shift were simultaneously found around the Tcin a EuBa2(Cu0.9957Fe0.01)3O7-dsuperconductor. These anomalous changes were attributed to phonon softening and low-temperature phase transformation occurring around the superconducting transition. Significant differences were observed between the57Fe Mössbauer spectra of superconducting EuBa2(Cu0.9957Fe0.01)3O7-dand the isostructural non-superconducting PrBa2(Cu0.9957Fe0.01)3O7-d. The differences were interpreted in connection with the suppression of superconductivity (by hole filling or hybridization of Pr, Cu and O states) in the Pr-containing compound. The unusually high isomer shift value observed in the Pr-containing material can give evidence for the charge transfer mechanism between the Cu(1) chains and the Cu(2) planes and for its role in the suppression of superconductivity.

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

Differential Thermal Analysis and PVT Measurements on 2,2,2-Trichloro-ethanol Under High Pressure

1997 ◽  
Vol 52 (6-7) ◽  
pp. 493-501 ◽  
Author(s):  
M. Jenau ◽  
M. Sandmann ◽  
A. Würflinger ◽  
J. Ll. Tamarit
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Atmospheric Pressure ◽  
Solid Phase ◽  
Melting Curve ◽  
Phase Behaviour ◽  
Enthalpy Changes ◽  
Pvt Measurements ◽  
Plastic Phase ◽  
Lower Temperature

Abstract The phase behaviour, the calorimetric and volumetric properties of 2,2,2-trichloro-ethanol (TCE) have been studied with differential thermal analysis (DTA) and pVT measurements in the pressure range 1 atm to 300 MPa and temperatures between 250 K to 355 K. TCE displays a metastable plastic phase (solid I') and a non-plastic solid phase II at atmospheric pressure. At least two pressure-induced solid phases have been detected: a stable plastic phase (solid I') and a non-plastic phase (solid III). There are two sets of triple points: a) 123 MPa and 308 K with the phases solid I, solid II and the liquid, b) 243 MPa and 316 K for solid I, II, III. Furthermore a metastable low-temperature brittle form (solid II') has been found, which transforms to solid I at a considerably lower temperature than solid II. The melting curve of solid I' can be pursued to higher pressures up to 260 MPa. On the other hand, the melting curve of the stable plastic phase solid I can be extrapolated beyond the triple point to pressures below 123 MPa. Volume and enthalpy changes are reported for all phase transitions.

scholarly journals NQR and Phase Transitions in Hexachlorocyclopropane Crystal

1990 ◽  
Vol 45 (3-4) ◽  
pp. 339-342 ◽  
Author(s):  
Masahiko Suhara ◽  
Koichi Mano
Keyword(s):  
Phase Transitions ◽  
Slow Rate ◽  
Metastable Phase ◽  
Phase Iii ◽  
Temperature Phase ◽  
Dsc Studies ◽  
Disordered Phase ◽  
Solid Phases ◽  
Low Temperature Phase ◽  
Phase Phase

Abstract35Cl NQR and DSC studies on phase transitions in hexachlorocyclopropane (HCCP), C3Cl6 , are reported. It is found that HCCP has three solid phases: A high temperature disordered phase (Phase I) above 301 K (no NQR spectrum was observed); a metastable phase (Phase II), which exhibited 6 NQR lines from 77 to 270 K; a low temperature phase (Phase III) in which a 24-multiplet of 35Cl NQR lines at 77 K, the most complex multiplet spectrum ever reported was observed. DSC measurement shows a A-type transition at 301 K and a broad transition of very slow rate at 285 K. The structure and mechanism of phase transitions in HCCP crystal are discussed.

1H NMR and Thermal Studies of CH3NH3Br in a Metastable Solid Phase Newly Found above 483 K

1989 ◽  
Vol 44 (8) ◽  
pp. 738-740 ◽  
Author(s):  
Masataka Tansho ◽  
Daiyu Nakamura ◽  
Ryuichi Ikeda
Keyword(s):  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Solid Phase ◽  
Thermal Studies ◽  
Stable Phase ◽  
Self Diffusion ◽  
H Nmr ◽  
Plastic Phase ◽  
Metastable Solid Phase ◽  
Absorption Measurements

Abstract By differential thermal analysis a new high-temperature solid phase of methylammonium bromide was found between 483 K and its “melting point” (510 K). 1H NMR absorption measurements revealed the presence of rapid 3D translational self-diffusion and overall rotation of methylammonium cations in this phase. These cationic motions are quite analogous to those of methylammonium iodide in its ionic plastic phase. Surprisingly, this plastic-like phase is metastable, the stable phase in the same temperature range being liquid.

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