Search results for "elastic neutron scattering"

Isostructural phase transition, quasielastic neutron scattering and magnetic resonance studies of a bistable dielectric ion-pair crystal [(CH3)2NH2]2…

2019

We have synthesised and characterised a novel organic–inorganic hybrid crystal, [(CH3)2NH2]2KCr(CN)6. The thermal DSC, TMA, DTG and DTA analyses indicate two solid-to-solid structural phase transitions (PTs). According to the X-ray diffraction experiments, the first PT at 220 K is isostructural, since it does not involve a change of the space group. This transition occurs between the states, where the (CH3)2NH2+ cations are orientationally disordered and ordered (frozen). The other reversible PT at 481 K leads to a melt-like phase similar to the one observed in plastic crystals or polar liquids. Dielectric spectroscopy has been used to characterise the switching properties of the dipole mom…

Diffusive motions in HD films physisorbed on graphite

2003

Abstract High-resolution quasielastic neutron scattering was used to study diffusive motions in two-dimensional liquid and solid phases of deuterium hydride submonolayers adsorbed on graphite (Papyex). For the first time it could be unambiguously clarified that the novel reentrant fluid phase at the commensurate–incommensurate transition has the character of a viscous fluid.

LaAg x In1?x

1980

The phonon dispersion of LaAg x In1−x (x=1, 0.89, 0.8) has been studied by inelastic neutron scattering in the cubic high temperature phase. A soft mode behaviour was observed at theM-point. The doubling and the cubic to tetragonal deformation of the elementary cell was observed through the phase transition. The measurements of the elastic constants were extended to 450 K and their magnetic field dependence was investigated.

Symmetry-species conversion in CD3systems

1993

The rates for symmetry-species conversion of CD3 groups are calculated using a model in which the interaction between the quadrupolar moment of the deuterons with electric-field gradient at the site of the nucleus causes symmetry-changing transitions. Just the same phonons are considered for energy conservation as are used to describe the temperature dependence of inelastic neutron scattering experiments. For the conversion rate, a similar temperature dependence is found as has already been obtained for CH3. For temperatures around the tunnelling energy, a behaviour is predicted for CD3 that is different from the behaviour in protonated systems according to all theories known to the authors…

NH3 dynamics in Zn(NH3)4I2 and Zn(NH3)4Br2 investigated by incoherent quasielastic neutron scattering

1997

We report on studies of NH3 dynamics in Zn(NH3)4I2 and Zn(NH3)4Br2 by means of incoherent quasielastic neutron scattering in the temperature range from 150 to 300 K. Quasielastic experiments were carried out on the Fermi chopper time-of-flight spectrometer at NIST. The Lorentzian full-widths at half-maximum, ƒw, of the quasielastic line follow an Arrhenius law and increase from 0.39 [0.25] meV at 150 K to 1.33 [0.80] meV at 300 K. We find an activation energy Ea for the NH3 reorientations of 32(1) and 30(3) meV for Zn(NH3)4I2 and Zn(NH3)4Br2, respectively.

MAGPACK1A package to calculate the energy levels, bulk magnetic properties, and inelastic neutron scattering spectra of high nuclearity spin clusters

2001

The Lineshape of Inelastic Neutron Scattering in Relaxor Ferroelectrics

2005

We show that a microscopic reason for the steep drop of the optical phonon branch into an acoustic one (the so-called waterfall effect) in relaxor ferroelectrics may be the coupling of phonons with defects and impurities of different kinds, which is always present in relaxors. Namely, we do not specify the type of impurities but rather represent them as an ensemble of so-called two-level systems (TLS). This approach makes it possible to trace the evolution of the “waterfall” with temperature and the TLS concentration. To facilitate the planning of experiments on inelastic neutron scattering, we present a modification of the so-called Latin hypercube sampling method, which, based on some sig…

Inelastic neutron scattering study of the rotational excitations in(KBr)1−x(KCN)xin the paraelastic and structural glass state

1984

The coupled rotational-translational excitations in ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ were studied by inelastic neutron scattering for concentrations $0.008\ensuremath{\le}x\ensuremath{\le}0.20$. We followed the ${A}_{1g}\ensuremath{-}{T}_{2g}$ tunneling transition and the ${A}_{1g}\ensuremath{-}{E}_{g}$ librational excitation through the transition from the paraelastic to the structural glass state. We found that these two excitations and their coupling to the lattice strains exhibit a very different temperature dependence in the glass state. While the tunneling transition, which triggers reorientations of the ${\mathrm{CN}}^{\ensuremath{-}}$ ions, shows a drastic r…

Spin Dynamics of the Half-Integer-Spin Quasi-One-Dimensional Heisenberg Antiferromagnet CsMnI3

1994

Magnetic excitations of CsMnI 3 , a quasi-one-dimensional Heisenberg antiferromagnet with S =5/2, have been measured by means of inelastic neutron scattering. Magnetic excitations in the low temperature phase are in good agreement with the predictions of the conventional linear spin-wave theory. In particular, in accordance with the linear spin-wave theory, we found three separate modes at Q =(0, 0, 1) instead of a threefold degenerate mode as seen in CsNiCl 3 ( S =1). It confirms that the spin dynamics of the integer spin value system are very different from those of the half-integer spin value system, even in their three-dimensionally ordered phase. Magnetic excitations in the intermediat…

Comparison of woods-saxon and double-folding potentials forα-particle scattering from54Fe at 24.5 MeV

1988

Inelastic-scattering data are presented forα-particles of 24.5 MeV from54Fe over the range 15° to 175° in the centre-of-mass system. The real part of the optical potential is calculated microscopically using the M3Y effective interaction of Bertschet al. and the DDM3Y density-dependent interaction. Elastic scattering has been analysed by using as real part of the optical potential M3Y, DDM3Y and Woods-Saxon forms (WS), taking in all three cases as imaginary part a WS potential. To fit the data the double-folding potential needs to be normalized by a factor of ⋍1.6 for the M3Y interaction and of ⋍1.13 for the DDM3Y interaction. By the study of the invariant-point ambiguity it has been observ…