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Lavrenčič, B. B.; Scott, J. F.

doi:10.1103/physrevb.24.2711

Cited by 16 publications

(6 citation statements)

References 27 publications

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“…The superlattice spots below 247 K appear at (0.40, 0, 0.5) instead of (0.39, 0.5, 0. this phase would be commensurate with the orthorhombic A2lam disordered phase. These results are in disagreement with [1] and could be sample dependent [2,3]. The authors of the first neutron scattering investigation [1] have recently repeated their measurements [4] which confirms their previous experiments : the phase below 247 K is incommensurate with a slight temperature dependence of the incommensurability [5] : the wave vector of the incommensurate modulation changes from qð (250 K) ~ 0.389 a* to q~ (120 K) ~ 0.394 a*.…”

contrasting

confidence: 93%

“…Points obtained by decreasing temperature fall on the same curve within the error bars. In the theory by Dvorak and Fousek for the structural transition of BaMnF4 [3], the spontaneous deformation uyz is a second order parameter which couples to the primary order parameter b y a term (lowest order coupling term : My~~). The change in the angular width can be directly compared to the intensity of the first order satellites obtained from neutron measurements.…”

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confidence: 99%

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Temperature dependence of the wave vector of the incommensurate modulation in two BaMnF4 crystals grown by different techniques ; neutron and X-ray measurements

et al. 1983

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Re_Cu le 20 mai 1983, revise le 6 juillet, accepte le 10 aout 1983) Résumé. 2014 Des mesures précises en diffusion des neutrons de la variation avec la température du vecteur d'onde incommensurable 03B4 dans deux cristaux de BaMnF4 sont présentées. Le rôle des défauts est mis en évidence par la présence d'hystérésis global et par la valeur, différente d'un échantillon à l'autre, de l'incommensurabilité résiduelle à basse température.Une faible déformation spontanée du réseau a été mise en évidence par une étude aux rayons X de la largeur des taches de Bragg.Cet effet est en accord avec la prédiction théorique d'une ferroélasticité pour T T0 (T0 ~ 250 K).Abstract 2014 Neutron elastic scattering measurements on two incommensurate BaMnF4 crystals show that the incommensurability 03B4 is temperature dependent. The large observed « global » hysteresis and the sample dependent residual value of the incommensurability at low temperature indicate the importance of lattice defects. A very small angular lattice distortion has been observed below T0 ~ 250 K by means of X-ray measurements of the width of some Bragg spots:This observation is in agreement with the theory of the structural transition in BaMnF4 which predicts the possibility of a ferroelastic strain below T T0.

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confidence: 93%

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confidence: 99%

Temperature dependence of the wave vector of the incommensurate modulation in two BaMnF4 crystals grown by different techniques ; neutron and X-ray measurements

et al. 1983

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“…This equation agrees with the relaxation time for the phason in a charge density wave system, as proposed by Bhatt and McMillan (1975); however, that agreement may be fortuitous inasmuch as their theory is for the commensurate phase, whereas the BaMnF, data are below Gin the incommensurate phase. As a follow-up to this experiment, Lavrencic and Scott derived the temperature dependence for a relaxation mode in the incommensurate phase of BaMnF, and obtained the same form (Lavrencic and Scott, 1981).…”

Section: Experimental Results In Incommensuratesmentioning

confidence: 92%

“…A temperature dependent diffusion time was derived for the phason in BaMnF, (Eq. 1.8)) (Lavrencic and Scott, 1981). The q-dependence of the diffusion time was not investigated.…”

Section: Discussionmentioning

confidence: 98%

Brillouin spectroscopy of the incommensurate—commensurate phase transition in barium sodium niobate

Young

Scott

1986

Phase Transitions

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Small angle and large-angle Brillouin scattering have been used to measure the sound velocity and damping of longitudinal waves propagating along (C, and perpendicular to (C'J the incommensurate axis in Ba,NaNb,O,, . For each mode strong dispersion is observed, with relaxation time 2 m of order 1.3 x lo-" s near T. For C , , T (~ satisfies with 2nr, = (1.08 & 0.13) x lo-'' s;2zr1 = (8.5 + 0.7) x lo-" s; and thediffusivity D = 1.3 cm'/s. This approximately 65 times larger than the thermal diffusivity of entropy fluctuations and implies a dynamic "central mode" for right-angle geometry light scattering of -60GHz. This mode is ten times the width observed for phason (soliton) diffusion by Lyons et al. in BaMnF,; it is not directly observed in the present work. For LA sound waves perpendicular to the incommensurate axis r;i(T) = T ; ' + Dq';that is, T, and D are the same as for C , , but ro' is neligible. T,, is interpreted as due to amplitude mode-acoustic mode interaction; T, and D are interpreted as interaction of acoustic modes with mobile defects, presumably soliton-like kinks in the incommensurate structure. +This paper summarizes the

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“…1), the structure of which is known from single-crystal X-ray (Effenberger & Pertlik, 1986) and neutron (Wilson, Cox & Stewart, 1991) techniques. This material undergoes a paraelectric-ferroelectric phase transition at 313 K (Lavrencic & Petzelt, 1977), and below this temperature the hydrogen atom gradually orders onto one of two initially equivalent sites, the ordering becoming complete some 100K or more below the transition temperature (Wilson, 1994). There are other structural changes as the symmetry is lowered from P2/c to Pc, but in this work only the hydrogen-atom ordering is considered.…”

Section: Introductionmentioning

confidence: 99%

Hydrogen-Atom Ordering in Lead Hydrogen Arsenate Monitored by Neutron Time-of-Flight Laue Diffraction using Single-Frame Methods

Wilson¹

1996

J Synchrotron Radiat

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The ordering of the hydrogen atom in a single crystal of lead hydrogen arsenate in the temperature range 320 to 80 K is described. The details of the ordering at small temperature steps are determined from single frames of data collected using the neutron time-of-flight Laue method. The constrained refinements obtained from these data yield lower precision than full data sets but allow the ordering to be characterized rapidly and reliably. This is the first example of the use of this single-frame method of monitoring such phase transitions. The approach used here with neutrons, stimulated in part by synchrotron Laue diffraction, will be of interest for all time-resolved experiments with synchrotron radiation or neutrons.

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Dynamical model for the polar-incommensurate transition in BaMnF4

Cited by 16 publications

References 27 publications

Temperature dependence of the wave vector of the incommensurate modulation in two BaMnF4 crystals grown by different techniques ; neutron and X-ray measurements

Temperature dependence of the wave vector of the incommensurate modulation in two BaMnF4 crystals grown by different techniques ; neutron and X-ray measurements

Brillouin spectroscopy of the incommensurate—commensurate phase transition in barium sodium niobate

Hydrogen-Atom Ordering in Lead Hydrogen Arsenate Monitored by Neutron Time-of-Flight Laue Diffraction using Single-Frame Methods

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