On the Order-Disorder Phase Transformation of Anilinium Halides.

1981 ◽  
Vol 36 (9) ◽  
pp. 967-974 ◽  
Author(s):  
Gerhard Fecher ◽  
Alarich Weiss ◽  
Gernot Heger
Keyword(s):  
Crystal Structure ◽  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Temperature Phase ◽  
Ordered Structure ◽  
Low Temperature Phase

Abstract The crystal structure of the low temperature phase of anilinium bromide, C6H5NH3⊕Br⊖, was studied by neutron diffraction at T = 100 K. The refinement supports an ordered structure. The structures of the low and high temperature phases are compared and the mechanism of the phase transformation is discussed.

Irreversible single-crystal to polycrystal and reversible single-crystal to single-crystal phase transformations in cyanurates

2001 ◽  
Vol 57 (6) ◽  
pp. 791-799 ◽  
Author(s):  
Menahem Kaftory ◽  
Mark Botoshansky ◽  
Moshe Kapon ◽  
Vitaly Shteiman
Keyword(s):  
Phase Transformation ◽  
High Temperature ◽  
Low Temperature ◽  
Single Crystal ◽  
High Temperature Phase ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Space Group ◽  
Reversible Phase ◽  
Low Temperature Phase

4,6-Dimethoxy-3-methyldihydrotriazine-2-one (1) undergoes a single-crystal to single-crystal reversible phase transformation at 319 K. The low-temperature phase crystallizes in monoclinic space group P21/n with two crystallographically independent molecules in the asymmetric unit. The high-temperature phase is obtained by heating a single crystal of the low-temperature phase. This phase is orthorhombic, space group Pnma, with the molecules occupying a crystallographic mirror plane. The enthalpy of the transformation is 1.34 kJ mol−1. The small energy difference between the two phases and the minimal atomic movement facilitate the single-crystal to single-crystal reversible phase transformation with no destruction of the crystal lattice. On further heating, the high-temperature phase undergoes methyl rearrangement in the solid state. 2,4,6-Trimethoxy-1,3,5-triazine (3), on the other hand, undergoes an irreversible phase transformation from single-crystal to polycrystalline material at 340 K with an enthalpy of 3.9 kJ mol−1; upon further heating it melts and methyl rearrangement takes place.

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.

Crystal Structure and NQR of Two Copper (I) Complexes of 4,6-Dimethylpyrimidine-2-thione

1994 ◽  
Vol 49 (1-2) ◽  
pp. 193-198 ◽  
Author(s):  
Sundara Ramaprabhu ◽  
Edwin A. C. Lucken ◽  
Gérald Bernardinelli
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Low Temperature ◽  
Phase Change ◽  
Temperature Dependence ◽  
High Temperature Phase ◽  
Symmetry Element ◽  
Temperature Phase ◽  
Crystallographic Study ◽  
Low Temperature Phase

Abstract The crystal structure and 63Cu NQR spectra of two neutral hexanuclear Cu(I) complexes of 4,6-dimethylpyrimidine-2-thione, (Hdmpt); [dmptCu]66CHCl3 (l) and [dmptCu]6C2H4Cl2 (2), are reported. The number and relative intensities of the NQR resonances are in agreement with the results of the crystallographic study. The temperature-dependence of the resonances reveals that both compounds undergo a phase-change in the temperature range 77 K -300 K, both of which may be associated with the loss of a symmetry-element present in the high-temperature phase. The 35Cl resonances of CHCl3 in 1 could be observed in the low-temperature phase but the corresponding resonances for C2H4Cl2 in 2 were not detected.

Investigation of an unusual low-temperature phase transformation in RbBH4 by neutron diffraction

2013 ◽  
Vol 203 ◽  
pp. 51-54 ◽  
Author(s):  
Brian B. Kitchen ◽  
Nina Verdal ◽  
Terrence J. Udovic ◽  
John J. Rush ◽  
Michael R. Hartman ◽  
...  
Keyword(s):  
Phase Transformation ◽  
Low Temperature ◽  
Neutron Diffraction ◽  
Temperature Phase ◽  
Low Temperature Phase
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