1,720,991 research outputs found
Kinetics of decomposition in ionic solids: neutron scattering study of the system AgBr-NaBr
No full textThe kinetics of decomposition in the quasibinary ionic system AgBr-NaBr has been studied by time-resolved neutron diffract ion and small-angle scattering. The temperature regimes for nucleation and for spinodal decomposition are dearly distinguished The coherent critical point is estimated as 458 +/- 5 K which is about 100 K below the maximum of the chemical binodal. Even at low temperatures the chemical demixing is completed within some 100 s resulting in a metastable state which is characterized by coherency strains and internal stresses of the order of 0.3 GPa. The mechanical relaxation of the lattice takes place on a much longer timescale after the correlation length of the decomposition pattern is increased to some critical value larger than 40 nm
Electric field induced intermediate phase near the ferroelectric lock-in transition in Rb2ZnCl4
No full textIn the presence of a strong external electric field, a diffuse intermediate phase is shown to exist in Rb2ZnCl4 between the incommensurate and the commensurate phases. High resolution gamma-ray diffraction in combination with in situ dielectric experiments yields detailed information about this unusual sequence of phase transitions that is most probably due to the accumulation of charged defects. The kinetics of field-induced transitions is studied by stroboscopic diffraction on a millisecond time-scale demonstrating that also mechanical strains play an important role for the transition mechanism
Visualising lattice vibrations: new features of the UNISOFT-program
No full textThe lattice dynamical program package UNISOFT had been developed as a tool for phenomenological model calculations and optimisation of experiments on phonon dispersion in the mid-1980's. In this paper we present a new version of UNISOFT which provides a number of new features. (C) 2000 Elsevier Science B.V. All rights reserved
Switching kinetics of the ferroelectric transition in K2SeO4 studied by stroboscopic gamma-ray diffraction
No full textThe kinetics of the ferroelectric lock-in transition in potassium selenate (K2SeO4) was studied on a millisecond timescale using high-resolution gamma-ray diffraction. A large change of the line width and wavevector of the first order satellite is observed during the switching process. This is attributed to a loss of long-range order under the influence of the electric field. In addition, the incommensurate phase is stabilized by the pulsed field and the transition to the pure commensurate phase is shifted to lower temperatures. Strains that may build up during the rapid switching process are supposed to be the reason for this behaviour.DFG [EC153/2-2
Influence of electric field and domain structure on the low-temperature Raman spectra of SrTiO3
No full textThe domain structure of SrTiO3 below its cubic to tetragonal phase transition depends not only on the stress-state of a particular sample but can also be modified very efficiently by the application of electric fields. Hence, the interpretation of field induced phenomena needs a careful consideration of the domain distribution which is often neglected in existing studies. In this paper, it is shown that the strong variation of polarized Raman spectra under external fields observed within both the para-electric tetragonal phase and the field induced ferroelectric phase, is a direct consequence of the redistribution of domains. Raman data can therefore be used to characterize the domain structure of a particular sample
Analytical approach to the 4D-resolution function of three axes neutron spectrometers with focussing monochromators and analysers
No full textThree axes neutron spectrometers explore excitations in condensed matter at almost arbitrary points within the 4-dimensional (Q-omega)-space of momentum and energy transfers. The knowledge of resolution is important for both, the preparation and interpretation of experiments. In order to meet the requirements of modem focussing techniques in direct and reciprocal spaces, an analytical algorithm is presented which allows the detailed calculation of the 4D-resolution function. This approach takes into account all essential features of state-of-the-art three axes spectrometers. Complementary to existing numerical simulation methods, the analytical treatment provides neutron users with almost instantaneous information about resolution effects of ongoing experiments. Moreover, it can be used as an efficient tool for the quantitative interpretation of experimental results. Several examples are shown which demonstrate the performance and the accuracy of the present approach. (C) 2014 Elsevier B.V. All rights reserved.German Federal Ministry for Education and Research (BMBF) [05K10MG2
Kinetics of the stress induced phase transition in quartz by real-time neutron scattering
No full textReal-time stroboscopic neutron scattering has been used to investigate the time evolution of the phase transition in quartz Under periodic external stresses relaxation times of the order 1 s are observed and the incommensurate phase exhibits a different stability regime as compared to static conditions. (C) 2000 Elsevier Science B.V. All rights reserved
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