Neutron structural study of the successive phase transitions in Rb<sub>2</sub>ZnCl<sub>4</sub>

Quilichini, M.; Pannetier, J.

doi:10.1107/s0108768183003183

Cited by 71 publications

(35 citation statements)

References 7 publications

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“…Pater, 1979), and in Rb2ZnCI 4 (Quilichini & Pannetier, 1983), K2ZnC14 (Mikhail & Peters, 1979), K2CoCI 4 (Vermin et al, 1976), (NH4)EZnCI4 (Matsunaga, 1982), CsECdBr 4 and CSEHgBr 4 (Altermatt, Arend, Gramlich, Niggli & Petter, 1984). Apart from these systematic differences, the variations in the distances in ZnBr 4 tetrahedra are much smaller than the modulation amplitudes of the Br atoms and the Zn atoms have small modulation amplitudes.…”

Section: Discussionmentioning

confidence: 93%

“…The phase-transition temperatures T i and T~ are 553 and 403 K for K2ZnCI 4 (Gesi &Iizumi, 1979), 303 and194 K for RbEZnCl 4 (Quilichini &Pannetier, 1983), and 129 and 94 K for KESeO 4 (lizumi, Axe, Shirane & Shimaoka, 1977). In addition, many other A2BX 4 compounds show incommensurately and commensurately modulated structures related to the modulated structure of Rb2ZnBr 4 (Hogervorst, 1986).…”

Section: Introductionmentioning

confidence: 99%

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Structural study of three modulated phases in Rb₂ZnBr₄

Hogervorst¹,

Helmholdt²

1988

Acta Crystallogr Sect B

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The crystal structures of Rb2ZnBr 4 at 293, 140 and 95 K have been studied using single-crystal X-ray diffraction or single-crystal neutron diffraction (for the structure at 95 K). The so-called incommensurate structure (293K) and the two threefold superstructures (140 and 95 K) have been determined using a computer program for modulated structures. The resulting 293 K structure has space group Pcmn-(00 y) (ssl). Because of conflicting symmetry evidence in the literature, several other space groups were tried, but they yielded less satisfactory results. For the other two phases, the space group Pc2~n was used. The R values are 0.08 (for 1512 main and 2654 satellite reflections), 0.12 (1494 + 3002 reflections) and 0.05 (for 502 + 980 reflections) for the structures at 293, 140 and 95 K respectively. There is no clear structural difference between the two threefold superstructure phases. The displacive modulation is strikingly similar in the three structures. It mainly consists of rotations of the rather rigid ZnBr 4 tetrahedra. The amplitude of the modulation functions is roughly 35% smaller in the 293 K structure than in the 95 K structure. The modulation functions of the two threefold superstructures show a strong pseudo-Pcmn(OOy)(ssi) symmetry. The temperature parameters clearly reveal that librations of the tetrahedra form an important component of the thermal vibrations. Crystal data at 95 (1)K: Mr= 555.9, a= 13.184 (4), b= 7.599 (2), c = 9.623 (5) A, V = 964.1 A 3.

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Section: Discussionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Structural study of three modulated phases in Rb₂ZnBr₄

Hogervorst¹,

Helmholdt²

1988

Acta Crystallogr Sect B

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“…Crystal structure analyses [10][11][12] reveal that there exist two possible orientations for the ZnCl4 groups that are occupied with equal probabilities and two corresponding sites for the Rb ions. We were able to identify the 2-site motion as reorientations of the ZnCI 4 between these orientations that are correlated with translational motions of Rb ions between the two sites.…”

Section: Rb 2-d Exchange-difference Nmr In Rb2zncl4mentioning

confidence: 99%

Magnetic resonance investigations of phase transitions and modulation wave motions in incommensurate solids

2000

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We measured R 'Rb nuclear magnetic resonance (NMR) and 35 C1 nuclear quadrupole resonance (NQR) Hahn spin-echo magnetization decays in the incommensurate (1) phase of Rb 2 ZnCl4 and, in each case, obtained a Hahn echo decay that was shorter than the Carr-Purcell-Meiboom-Gill decay and one which decayed with a time constant proportional to the cube of the echo time. From these measurements we obtained from both the s 'Rb NMR and "Cl NQR measurements values for the diffusion coefficients that are comparable in magnitude, a fact that strongly supports the existence of slow modulation wave diffusionlike motions in the I phase, since such motions should affect both Rb and Cl ions similarly. In addition, we used "'Rb two-dimensional exchange-difference NMR to study atomic motions in the incommensurate (I) and paraelectric (P) phases to elucidate the nature of the I -P transition. We measured as a function of the mixing time the frequency shifts of the cross peaks from the main diagonal and observed a gradual increase towards an asymptotic value in the I phase but a sudden jump to the final value in the P phase. We interpreted the motions observed in the P phase as normal modes arising from simultaneous reorientations of ZnC1 4 tetrahedra and corresponding Rb ions displacements between two sites. These normal modes freeze out in the I phase and change to the diffusionlike motion of the modulation wave. We also performed 35 C1 NQR lineshape and Ti measurements in K 2 ZnCi4 and obtained conclusive evidence for the presence of a narrow lq (singly modulated) T phase between 146 and 149 K.

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“…Rb 2 ZnCl 4 belongs to the family of A 2 BX 4 crystals with the β-K 2 SO 4 structure that exhibits several successive phase transitions that have been experimentally measured [1][2][3][4][5][6] and theoretically predicted [7][8][9][10][11]. Above 303 K, Rb 2 ZnCl 4 exists in the high temperature normal (N ) phase, which is orthorhombic, belonging to space group Pnma-D 16 2h [2] and containing four formula units per unit cell.…”

Section: Introductionmentioning

confidence: 98%

A Study of the Incommensurate Phase of Rb₂ZnCl₄by ESR

Agirtmis¹,

Farach²,

Creswick

et al. 2004

Ferroelectrics

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The ESR absorption spectrum of Mn 2+ ions at Zn positions has been studied in the incommensurate phase of Rb 2 ZnCl 4 . It is known that Rb 2 ZnCl 4 crystals exhibit an incommensurate phase between temperatures T i = 303 K and T l = 192 K. The form and the temperature dependence of ESR spectra are in good agreement with the predictions of the phase soliton theory. The parameters h 1 and h 2 determining the magnetic resonance field show, as expected, a power law as a function of the temperature. A modified superposition model was used to estimate the modulation amplitude of the incommensurate phase, and the principal axis of the zero field splitting D.

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Neutron structural study of the successive phase transitions in Rb₂ZnCl₄

Cited by 71 publications

References 7 publications

Structural study of three modulated phases in Rb₂ZnBr₄

Structural study of three modulated phases in Rb₂ZnBr₄

Magnetic resonance investigations of phase transitions and modulation wave motions in incommensurate solids

A Study of the Incommensurate Phase of Rb₂ZnCl₄by ESR

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Neutron structural study of the successive phase transitions in Rb2ZnCl4

Cited by 71 publications

References 7 publications

Structural study of three modulated phases in Rb2ZnBr4

Structural study of three modulated phases in Rb2ZnBr4

Magnetic resonance investigations of phase transitions and modulation wave motions in incommensurate solids

A Study of the Incommensurate Phase of Rb2ZnCl4by ESR

Contact Info

Product

Resources

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Neutron structural study of the successive phase transitions in Rb₂ZnCl₄

Structural study of three modulated phases in Rb₂ZnBr₄

Structural study of three modulated phases in Rb₂ZnBr₄

A Study of the Incommensurate Phase of Rb₂ZnCl₄by ESR