14N and35Cl nuclear quadrupole double resonance study of the structural phase transitions in N-octylammoniumchloride

1987 ◽  
Vol 67 (3) ◽  
pp. 363-368 ◽  
Author(s):  
J. Seliger ◽  
V. Žagar ◽  
R. Blinc ◽  
R. Kind ◽  
H. Arend ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Double Resonance ◽  
Structural Phase Transitions ◽  
Nuclear Quadrupole

NQR study of the structural phase transitions in a system with reduced effective dimensionality: K2ReCl6

1983 ◽  
Vol 61 (10) ◽  
pp. 1374-1381 ◽  
Author(s):  
Marie D'Iorio ◽  
Robin L. Armstrong
Keyword(s):  
Fourier Transform ◽  
Phase Transitions ◽  
Hydrostatic Pressure ◽  
Magnetic Resonance ◽  
Structural Phase ◽  
Nonlinear Phenomena ◽  
Structural Phase Transitions ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole ◽  
Effective Dimensionality

Chlorine 35 nuclear quadrupole resonance (NQR) frequency and lineshape data, obtained with a Fourier transform magnetic resonance spectrometer, are presented for the antifluorite crystal K2ReCl6. In the temperature range investigated, 85 to 130 K, two structural phase transitions occur which reduce the crystal symmetry from cubic to tetragonal to monoclinic. The variation of the NQR spectrum with temperature and with hydrostatic pressure up to 2.64 kbar is documented. The structure of the spectrum and the intensity distribution within it are unexpected from previous studies of antifluorite systems. An explanation of the results is given which is based on recent discussions of nonlinear phenomena at phase transitions in crystals exhibiting reduced effective dimensionality.

Neutron-diffraction study of the structural phase transitions in the antifluorite K2PtBr6

1985 ◽  
Vol 63 (7) ◽  
pp. 988-996 ◽  
Author(s):  
Robin L. Armstrong ◽  
Rose M. Morra ◽  
Brian M. Powell
Keyword(s):  
Phase Transitions ◽  
Nuclear Quadrupole Resonance ◽  
Goodness Of Fit ◽  
Structural Phase ◽  
Spectral Characteristics ◽  
Neutron Diffraction Study ◽  
Structural Phase Transitions ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

Neutron-powder-diffraction profiles are reported for the antifluorite K2PtBr6 at temperatures of 296, 160, 141, and 120 K. Bromine nuclear-quadrupole-resonance measurements have shown that each of these temperatures corresponds to a different crystal structure and have provided information on the most probable structures. A variety of structural models with symmetries obtained from a group theoretical classification of structural phase transitions are fitted to the diffraction data. A comparison of goodness-of-fit parameters for the models considered at each temperature allows the space group of each phase to be identified. The results provide (i) a definitive test of the validity of a classification scheme proposed for nuclear-quadrupole-resonance spectral characteristics, and (ii) support for the proposition that the allowable, continuous distortions of a crystal are given by the nondisruptive criterion rather than the more restrictive group–subgroup criterion.

Evidence for precursor clusters associated with structural phase transitions in antifluorite crystals

1982 ◽  
Vol 60 (4) ◽  
pp. 397-398 ◽  
Author(s):  
Robin L. Armstrong ◽  
Marie D'Iorio ◽  
Maximo E. Ramia
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Indirect Evidence ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
Type Phase ◽  
Symmetry Phase ◽  
Nuclear Quadrupole ◽  
Low Symmetry

Measurements of the temperature dependence of the intensities of the halogen nuclear quadrupole resonances in K2PtBr6 and K2ReCl6, in the cubic phase are reported. These results provide indirect evidence for the formation of dynamic clusters of the low symmetry phase as a precursor to the occurrence of rotative type phase transitions to tetragonal structures in these crystals.

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