Effect of pressure on the temperature of the displacive to order–disorder crossover associated with the structural phase transition in K2OsCl6

1990 ◽  
Vol 68 (1) ◽  
pp. 88-90 ◽  
Author(s):  
Robin L. Armstrong ◽  
Marcin Krupski ◽  
Sunyu Su
Keyword(s):  
Phase Transition ◽  
Hydrostatic Pressure ◽  
Nuclear Quadrupole Resonance ◽  
Structural Phase Transition ◽  
Resonance Spectrum ◽  
Structural Phase ◽  
Effect Of Pressure ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole ◽  
Rotational Phase

The 35Cl nuclear quadrupole resonance spectrum of K2OsCl6 is studied as a function of applied hydrostatic pressure in the temperature range bracketing the temperature of the rotational phase transition. The data suggest that the effect of increasing pressure is to increase the lattice dimensionality of the correlated rotational fluctuations that drive this phase transition.

Effect of hydrostatic pressure on the structural phase transition in K2OsCl6:a35Cl nuclear quadrupole resonance

1987 ◽  
Vol 65 (2) ◽  
pp. 134-137 ◽  
Author(s):  
Marcin Krupski ◽  
Robin L. Armstrong ◽  
Mariusz Maćkowiak ◽  
Maria Zdanowska-Fraczek
Keyword(s):  
Phase Transition ◽  
Nuclear Quadrupole Resonance ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Pressure Coefficient ◽  
Nuclear Quadrupole Resonance Frequency ◽  
Rigid Sphere ◽  
Cubic Phase ◽  
Quadrupole Resonance ◽  
Nuclear Quadrupole

The 35Cl nuclear quadrupole resonance frequency is reported in K2OsCl6 at temperatures in the vicinity of the structural phase transition for three externally applied hydrostatic pressures. The phase-transition temperature, Tc, decreases linearly with pressure, and the pressure coefficient, (dTc/dP), is measured to be −(2.2 ± 0.3) × 10−2 K∙MPa−1. This value is compared with that measured for K2ReCl6 and is consistent with the prediction of a calculation based on a modified rigid-sphere model. Measurements of (∂v/∂P)T show precursor behaviour as Tc is approached from the high-temperature cubic phase.

Nitrogen-14 Nuclear Quadrupole Resonance in Some Hexanitro Complexes of the Type R2PbCu(NO2)6

1979 ◽  
Vol 34 (12) ◽  
pp. 1722-1728 ◽  
Author(s):  
Tetsuo Asaji ◽  
Ryuichi Ikeda ◽  
Daiyu Nakamura
Keyword(s):  
Phase Transition ◽  
Nuclear Quadrupole Resonance ◽  
Ammonium Salt ◽  
Complex Anion ◽  
Structural Phase ◽  
Three Phase ◽  
Quadrupole Resonance ◽  
Quadrupole Parameters ◽  
Nuclear Quadrupole ◽  
Nitrogen Bonds

The nuclear quadrupole resonance of nitrogen-14 was observed for potassium, ammo­nium, rubidium, and thallium lead hexanitrocuprates(II) at various temperatures below the second highest transition temperature of each complex. All the compounds except the ammonium salt yielded two practically same sets of the quadrupole parameters, eQq/h and η, indicating the presence of at least two crystallographically different but very similar kinds of nitrogen atoms in the crystals. For the ammonium salt, three phase transitions at 94.5, 287, and 316 K were located from the experiments of DTA and NQR. The crystals of the highest and the second highest temperature phases were proved to be i8omorphous with those of the remaining complexes in their highest and intermediate temperature phases, respectively. The salt yielded two sets of the quadrupole parameters between 287 and 94.5 K, and only one sot below 94.5 K down to 4.2 K, indicating that a structural phase transition takes place at 94.5 K. No resonance could be observed in the highest and the second highest temperature phases of all the complexes studied. The covalency of copper-nitrogen bonds in lead hexanitrocuprates(II) is estimated at about 10% from the quadrupole parameters observed at 4.2 K. The structure of the complex anion is discussed in relation to the Jahn-Toller distortion.

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.

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