NMR-NQR studies of structural phase transitions

Rigamonti, A.

doi:10.1080/00018738400101651

Cited by 139 publications

(53 citation statements)

References 335 publications

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“…This is very different behavior from what has been observed in many other displacive phase transitions. In most cases, T~ decreases with increasing temperature up to the phase transition, and then increases with increasing temperature above the transition (Rigamonti 1984). The relaxation time in these cases is usually related to a vibrational soft mode that hardens above the transition temperature, and this behavior has been observed for both spin 1/2 (e.g.…”

Section: Quartzmentioning

confidence: 94%

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Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

1992

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Abstract. Relaxation times (T1) and lineshapes were examined as a function of temperature through the c~-// transition for z9si in a single crystal of amethyst, and for 29Si and 170 in cristobalite powders. For single crystal quartz, the three z9Si peaks observed at room temperature, representing each of the three differently oriented SiO, tetrahedra in the unit cell, coalesce with increasing temperature such that at the c~-//transition only one peak is observed. 29Si Tl's decrease with increasing temperature up to the transition, above which they remain constant. Although these results are not uniquely interpretable, hopping between the Dauphin6 twin related configurations, el and ez, may be the fluctuations responsible for both effects. This exchange becomes observable up to 150~ below the transition, and persists above the transition, resulting in//-quartz being a time and space average of el and e2. 298i Tl's for isotopically enriched powdered cristobalite show much the same behavior as observed for quartz. In addition, 170 Tl's decrease slowly up to the e-// transition at which point there is an abrupt 1.5 order of magnitude drop. Fitting of static powder ~70 spectra for cristobalite gives an asymmetry parameter (t/) of 0.125 at room T, which decreases to <0.040 at the transition temperature. The electric field gradient (EFG) and chemical shift anisotropy (CSA), however, remain the same, suggesting that the decrease in t/is caused by a dynamical rotation of the tetrahedra below the transition. Thus, the mechanisms of the e-// phase transitions in quartz and cristobalite are similar: there appears to be some fluctuation of the tetrahedra between twin-related orientations below the transition temperature, and the//-phase is characterized by a dynamical average of the twin domains on a unit cell scale.

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Section: Quartzmentioning

confidence: 94%

“…NMR has been used extensively to study the dynamics of phase transitions in crystalline solids (Borsa and Rigamonti 1990;Rigamonti 1984;Blinc 1981). However, it has not yet been widely applied to the study of phase transitions in silicates.…”

Section: Nmr and Phase Transitionsmentioning

confidence: 99%

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

1992

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“…Calculation of the spectral density is here based on a collective coordinate representation of the hydrogen bond fluctuations connected with a soft lattice mode. Excellent and comprehensive reviews of the theoretical concepts, as well as of the experimental verifications can be found in [20,21].…”

Section: Spin-lattice Relaxation and Critical Behaviourmentioning

confidence: 99%

Evidence for Ferroelectric Nucleation Centres in the Pseudo-spin Glass System Rb1−x (ND4) x D2PO4: A 87Rb NMR Study

Kind

2006

Structure and Bonding

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“…This leads to two limiting cases; the high frequency local field fluctuation with small amplitudes on the one hand and the infrequent and large amplitude fluctuation of the local field on the other hand. The so-called Fweak collision_ approach is relevant to the former case while to the latter case the Fstrong collision_ approach is applicable [3]. Following the general procedure, the weak collision approach yields the relaxation rates in the fast motion regime frequency region with increasing impurity concentration, may be explained in terms of the local point symmetry in the crystal and the probability for the impurities to occupate the lattice sites around the symmetry points.…”

Section: Introductionmentioning

confidence: 99%

Comparison of the Impurity Effects on Lattice Dynamics in K2SnCl6 between Isomorphic and Nonisomorphic Systems Near the Structural Phase Transition Temperature Revealed by Nuclear Resonance

et al. 2005

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Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (KYRb) 2 SnCl 6 and K 2 (SnYRe)Cl 6 and the nonisomorphic system K 2 SnCl 6 :Al 3+ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.

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NMR-NQR studies of structural phase transitions

Cited by 139 publications

References 335 publications

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

Dynamics of the ?-? phase transitions in quartz and cristobalite as observed by in-situ high temperature 29Si and 17O NMR

Evidence for Ferroelectric Nucleation Centres in the Pseudo-spin Glass System Rb1−x (ND4) x D2PO4: A 87Rb NMR Study

Comparison of the Impurity Effects on Lattice Dynamics in K2SnCl6 between Isomorphic and Nonisomorphic Systems Near the Structural Phase Transition Temperature Revealed by Nuclear Resonance

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