High-pressure nuclear quadrupolar resonance study of dynamical effects associated with the structural phase transition in K2OsCl6

1989 ◽  
Vol 67 (6) ◽  
pp. 566-571 ◽  
Author(s):  
Marcin Krupski ◽  
Robin L. Armstrong
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Soft Mode ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Central Peak ◽  
Spin Lattice Relaxation ◽  
Detectable Effect ◽  
Spin Lattice ◽  
Lattice Mode

A new design for a nuclear quadrupolar resonance probe to study solids subjected to high hydrostatic pressures at low temperatures is presented. Measurements of the 35Cl spin-lattice relaxation are reported at three pressures in the temperature range just above the structural phase transition in the antifluorite crystal K2OsCl6. These data are influenced by the softening of the rotary lattice mode and the evolution of a dynamic central peak. A small pressure dependence of the correlated fluctuations associated with the soft mode is observed; however no detectable effect on the correlated fluctuations associated with the dynamic disorder component of the central peak is seen.

The Observation of a Displacive Phase Transition in (NH4)2PtBr6

1973 ◽  
Vol 51 (8) ◽  
pp. 781-786 ◽  
Author(s):  
Maria Wiszniewska ◽  
Robin L. Armstrong
Keyword(s):  
Phase Transition ◽  
Relaxation Time ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Tetragonal Symmetry ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
Lattice Mode

Measurements of the 79Br nuclear quadrupole resonance frequency and spin–lattice relaxation time in a polycrystalline sample of (NH4)2PtBr6 from 4 to 450 K are reported. The frequency data indicate the occurrence of a structural phase transition at 58 K. The spin–lattice relaxation time data exhibit a distinct minimum, also at 58 K. The data are discussed in terms of a model previously introduced to account for phase transitions from cubic to tetragonal symmetry in R2MX6 compounds. A point charge calculation provides an explanation of the observed frequency splitting in terms of the alteration in the neighboring ion contribution to the electric field gradient at the 79Br nuclear sites. This alteration results from a small distortion of the cages defined by the NH4 ions and an accompanying rotation of the PtBr6 octahedra situated within these cages. The temperature dependences of two different average rotary lattice mode frequencies are deduced; in each case the observed behavior supports the hypothesis that it is the rotary lattice mode which softens thereby bringing about the change in structure.

Chlorine-35 NQR Study of a Structural Phase Transition in (ND4)2PdCl6

1998 ◽  
Vol 53 (6-7) ◽  
pp. 514-517 ◽  
Author(s):  
Yoshio Kume ◽  
Tetsuo Asaji
Keyword(s):  
Phase Transition ◽  
Structural Phase ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Temperature Phase ◽  
Spin Lattice ◽  
First Order Phase Transition ◽  
Temperature Dependences ◽  
First Order Phase

Abstract Temperature dependences of 35Cl NQR frequencies and spin-lattice relaxation times were measured at 4.2 to 400 K for natural and deuterated ammonium hexachloropalladate. It was confirmed that only the deuterated salt undergoes a first order phase transition at 30 K. The crystal structure of the low-temperature phase is predicted to be the same as that of the deuterated ammonium hexachloroplatinate and hexachloroplumbate. The mechanism of the deuteration-induced phase transition is discussed.

Chlorine-NQR Relaxation Near the Structural Transitions of Natural and Deuterated (NH4)2TeCl6

1992 ◽  
Vol 47 (1-2) ◽  
pp. 261-264 ◽  
Author(s):  
C. Dimitropoulos ◽  
F. Borsa ◽  
J. Pelzl
Keyword(s):  
Phase Transition ◽  
Relaxation Rate ◽  
Critical Region ◽  
Soft Mode ◽  
Lattice Relaxation ◽  
Relaxation Mechanism ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Trigonal Phase ◽  
Strongly Damped

AbstractThe temperature and isotope dependence of the 35,37Cl-NQR spin-lattice relaxation rate near the cubic to trigonal phase transition at Tc1 ≌ 87 K has been investigated in both (NH4) 2TeCl6 and (ND4)2TeCl6 salts. In the temperature range of ~ 20 K above and ~ 10 K below TCl, the relaxation obeys the relation (T1 • T)2 ∞(T-TCl). This behaviour corresponds to a direct relaxation mechanism in presence of a strongly damped rotational soft mode of the TeCl26- tetrahedra and is discussed on the basis of cation-anion coupling near the critical region. Below TCl we observe an extra contribution to the 35,37Cl relaxation rate which is tentatively ascribed to the dynamics of the NH4+ tetrahedra.

NQR Investigation of Anion Dynamics in Rb2Zn(Cl1 - xBrx)4

1996 ◽  
Vol 51 (5-6) ◽  
pp. 745-750 ◽  
Author(s):  
R. K. Subramanian ◽  
S. Uma Maheswari ◽  
K. Venu ◽  
V. S. S. Sastry
Keyword(s):  
Phase Transition ◽  
Dominant Role ◽  
Structural Phase ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Cation Substitution ◽  
Spin Lattice ◽  
Quadrupole Resonance ◽  
Anion Impurity

Abstract The structural stability of Rb2Zn(Cl1 - xBrx)4 (x = 1% and 3%) is investigated using the 35Cl quadrupole resonance frequency and spin lattice relaxation time (T1Q) in the paraelectric (PE) phase. The PE to incommensurate (IC) phase transition temperature T1, observed at 302 K in the pure compound, is lowered to 300 K for x = 1 % and to 293 K for x = 3%. These effects are smaller than in the earlier reported case of 3% Cs substitution in Rb2ZnCl4 , which reduces T1 by 25 K. While bigger cation substitution affects only the barrier for anion dynamics about directions perpendicular to the a-axis (direction of low temperature IC modulation wave), bigger anion substitution is found to affect the barrier for anion dynamics about the a-axis as well. The present study also indicates that the cusp like dip in T1Q observed while approaching T1 from above (characterizing the soft mode condensation associated with the structural phase transition) is essentially unaffected by anion impurity substitution, in contrast to the case where bigger cation substitution tends to smear the transitional effects. These results seem to suggest the dominant role played by cations in stabilizing the PE phase of these A2BX4 systems, in comparison to anions.

scholarly journals Raman spectroscopy study of the behavior of the soft mode in a structural phase transition in the Pr3Sb5O12 crystal

2015 ◽  
Vol 57 (11) ◽  
pp. 2286-2289 ◽  
Author(s):  
A. S. Oreshonkov ◽  
A. K. Khodzhibaev ◽  
A. S. Krylov ◽  
M. F. Umarov ◽  
A. N. Vtyurin
Keyword(s):  
Phase Transition ◽  
Raman Spectroscopy ◽  
Structural Phase Transition ◽  
Soft Mode ◽  
Structural Phase ◽  
Spectroscopy Study
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