Neutron scattering investigation of incommensurate ThBr<sub>4</sub>

Bernard, L.; Currat, R.; Delamoye, P.; Zeyen, C. M. E.; Hubert, S.; Kouchkovksy, R de

doi:10.1088/0022-3719/16/3/007

Cited by 94 publications

(53 citation statements)

References 17 publications

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“…In only a few cases are both components Cl and C2 known: in ThBr4 an optic and acoustic mode (Bernard, Currat, Delamoye, Zeyen, Hubert & de Kouchovsky 1983), in NaNO2 the NO2 ordering and an xy shear (Kucharczyk, Pietrasko & Lukaszewicz 1978a, b), in the mineral mullite and the intermediate plagioclase feldspars two different ordering patterns (McConnell, 1978(McConnell, , 1981(McConnell, a, 1984a. Other cases include K2PbCu(NO2)6 (Noda, Mori & Yamada, 1978;McConnell & Heine, 1982), thio-urea (Parlinski & Michel, 1984) and nepheline (McConnell, 1981b(McConnell, , 1984b.…”

Section: Introduction: the Use Of Two-component Structuresmentioning

confidence: 99%

“…For example, it allows us to fix immediately the phase of the shear wave in NaNO2 which was found by Kucharczyk et al (1978) but whose phase was left undetermined by these authors: it should be displaced by a quarter wavelength from the suggested position shown in their sketch. While such symmetry requirements have been used directly or indirectly in a few specific cases like ThBr4 (Bernard et al, 1983) we wish to develop them here in their generality. The symmetry connection (1.3) is almost obvious from Fig.…”

Section: Introduction: the Use Of Two-component Structuresmentioning

confidence: 99%

“…Sometimes (?2 does not only have the symmetry of grad C~, it actually is grad Ci, e.g. in ThBr4 (Bernard et al, 1983).…”

Section: Introduction: the Use Of Two-component Structuresmentioning

confidence: 99%

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An aid to the structure analysis of incommensurate phases

McConnell¹,

Heine²

1984

Acta Cryst Sect A

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Section: Introduction: the Use Of Two-component Structuresmentioning

confidence: 99%

Section: Introduction: the Use Of Two-component Structuresmentioning

confidence: 99%

See 1 more Smart Citation

An aid to the structure analysis of incommensurate phases

McConnell¹,

Heine²

1984

Acta Cryst Sect A

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“…Below this temperature, neutron diffraction measurements (Bernard et al, 1983;Currat, Bernard & Delamoye, 1986) show the presence of weak first-order satellites, which indicates a structural distortion with wavevector q = 0.32e*. No lock-in transition has been detected within the temperature range 95 to 1.5 K. Weak second-order satellites seemed to be observed at very low temperatures (Currat, Bernard & Delamoye, 1986) but they could not be accurately measured.…”

Section: Introductionmentioning

confidence: 94%

“…The high site symmetry of Th and Br atoms and the direction of the modulation wavevector simplifies its structural distortion. On the other hand, phase and amplitude branches have been clearly observed by inelastic neutron scattering (Bernard et al, 1983;Currat, Bernard & Delamoye, 1986).…”

Section: Introductionmentioning

confidence: 99%

Phasons modulate the atomic Debye–Waller factors in incommensurate structures: experimental evidence in ThBr₄ at 55 K

Madariaga¹,

Pérez-Mato²,

Aramburu³

1993

Acta Crystallogr Sect B

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The incommensurate displacive structure of fl-ThBr4 at 55 K has been determined from a neutron diffraction data set including main reflections and firstorder satellites. The superspace group is DI4damdJr-s-f sl.Final agreement factors are 0.0193, 0.0186 and 0.045 for all, main and satellite reflections, respectively. It is shown that the effect of phasons on the atomic Debye-Waller factors can be quantified by two additional structural parameters: the modulus Br fill.2 and the phase Br XI1.2 of a second harmonic that spatially modulates the temperature factors of Br atoms. Results are in good agreement, within the resolution of the experimental data, with the theoretically expected value for Br X IL2. Crystal data for the average structure: Mr=551.65, tetragonal, 141/amd, a= 8.919(1), c=7.902(1) A, V=628.6(2) A 3, Z=4,

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Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U⁴⁺–ThCl₄ System

Krupa¹,

Malek²,

Delamoye³

et al. 1987

Physica Status Solidi (b)

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The second order phase transition in P-ThC14 (T, = 70 K) leads to an incommensurate tetragonal structure modulated along the fourfold symmetry axis. This is due to the freezing of an optical soft mode which induces a modulation of the chlorine ion positions in a plan perpendicular to this axis. Consequently in neighbouring unit cells the crystal field strength acting on the U4+ ion is slightly different. Then the line shape in the optical spectra shows a continuous variation which reflects the shift of the energy as the symmetry changes. Selective excitation of the resulting different classes of sites, S,, D,, and various C,p ermits one to establish a correlation between absorption and emission profiles of U4+ ions. The green and the red observed fluorescences of U4+ in ThCl, are assigned in the different symmetries and the energy level mapped out as a function of a phase angle ql related to the distortion according to the Delamoye and Currat model.Der Phasenubergang zweiter Ordnung in P-ThCl, (T, = 70 K) fuhrt zu einer inkommensurablen tetragonalen Struktur, die in Richtung der vierfachen Symmetrieachse moduliert ist. Dies riihrt vom Susfrieren einer optiscben Soft-Mode her, die eine Modulation der Chlorionenplatze in einer Ebene senkrecht zu dieser Achse induziert. Folglich ist in den benachbarten Einheitszellen die auf das U4+-Ion wirkende Kristallfeldstarke leicht unterschiedlich. Somit zeigt die Linienform in den optischen Spektren eine kontinuierliche Anderung, die die Verschiebung der Energie widerspiegelt, wenn sich die Symmetrie andert. Selektive Anregung der sich ergebenden unterschiedlichen Klassen der Platze S,, D, und verschiedene C,, erlaubt, eine Korrelation zwischen Absorptions-und Emissionsprofilen der U4f-Ionen aufzustellen. Die beobachtete grune und rote Fluoreszenz von U4+ in ThCl, in den verschiedenen Symmetrien werden zugeordnet und die Energieniveaus als Funktion eines Phasenwinkels ql dargestellt, der entsprechend dem Model1 von Delamoye und Currat mit der Verzerrung verkniipft ist.

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Neutron scattering investigation of incommensurate ThBr₄

Cited by 94 publications

References 17 publications

An aid to the structure analysis of incommensurate phases

An aid to the structure analysis of incommensurate phases

Phasons modulate the atomic Debye–Waller factors in incommensurate structures: experimental evidence in ThBr₄ at 55 K

Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U⁴⁺–ThCl₄ System

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Neutron scattering investigation of incommensurate ThBr4

Cited by 94 publications

References 17 publications

An aid to the structure analysis of incommensurate phases

An aid to the structure analysis of incommensurate phases

Phasons modulate the atomic Debye–Waller factors in incommensurate structures: experimental evidence in ThBr4 at 55 K

Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U4+–ThCl4 System

Contact Info

Product

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About

Neutron scattering investigation of incommensurate ThBr₄

Phasons modulate the atomic Debye–Waller factors in incommensurate structures: experimental evidence in ThBr₄ at 55 K

Observation of an incommensurate structure by optical spectroscopy with a 5f ion as an internal probe. U⁴⁺–ThCl₄ System