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A Klopperpieper - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic Effects of Bromine Substitution in Betaine Calcium Chloride Dihydrate
    Ferroelectrics, 2004
    Co-Authors: L. G. Vieira, J. L. Ribeiro, M. R. Chaves, M. Quilichini, Olivier Hernandez, Agostinho Almeida, A Klopperpieper
    Abstract:

    The effects of partial substitution of chlorine by bromine in incommensurate betaine Calcium Chloride di-hydrate (BCCD) have been investigated by FTIR reflectivity and elastic neutron scattering. Bromine distorts the H-bonds linking the Ca complexes and induces local symmetry breaking. The temperature dependence of b and c lattice parameters of the 4% and 8% brominated compounds reveals that this distortion has effects that are markedly anisotropic. This anisotropy may help to clarify why bromine progressively destabilizes the low temperature phases of BCCD.

  • Hydrogen bonds behaviour in brominated betaine Calcium Chloride Dihydrate
    Ferroelectrics, 2002
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, A. Almeida, Filipa Pinto, Pedro Teles, L. M. Rabkin, A Klopperpieper
    Abstract:

    The results of a comparative Raman scattering study of pure and Br - doped betaine Calcium Chloride Dihydrate (BCCD) in the 12-300 K temperature range are reported. It is shown that bromine weakens hydrogen bonding, preventing in this way the localization of protons at low temperatures. Consequently for a high enough content of bromine, the non modulated ferroelectric phase is missing.

  • On the T s Anomaly in Betaine Calcium Chloride Dihydrate (BCCD)
    Ferroelectrics, 2002
    Co-Authors: J. L. Ribeiro, M. R. Chaves, L. G. Vieira, Olivier Hernandez, A. Almeida, P. Thuery, A Klopperpieper
    Abstract:

    In this work we study the structure of the fourfold phase in a 2% brominated BCCD sample, above and below the so-called "strange anomaly" at T s , 93 K, in order to confirm the structural modification predicted by Neubert et al . on the basis of the Double Ising Spin model. The "internal transition" predicted by this model would correspond to a first order, symmetry conserving phase transition, that preserves the wavenumber of the commensurate phase and is characterized by a discontinuous increase of the symmetrized components of the structural modulation. The experimental results reported herein do not corroborate the quantitative predictions of the model.

  • influence of bromine on the incomplete devil s staircase behavior of betaine Calcium Chloride Dihydrate
    Physical Review B, 2001
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, A. Almeida, Filipa Pinto, A Klopperpieper
    Abstract:

    The results of a comparative Raman study of pure and ${\mathrm{Br}}^{\ensuremath{-}}$-doped betaine Calcium Chloride Dihydrate in the temperature interval 12--292 K are presented. The analysis of the low-frequency Raman spectra at room temperature revealed that the lowest-frequency phonons are associated with the betaines' vibrations whereas the lattice modes sensitive to ${\mathrm{Cl}}^{\ensuremath{-}}/{\mathrm{Br}}^{\ensuremath{-}}$ substitution are found above 44 ${\mathrm{cm}}^{\ensuremath{-}1}.$ The mechanisms responsible for the incommensurate phase are not strongly affected by bromination in contrast with what happens in the commensurate phases. It is shown that bromine weakens hydrogen bonding, preventing the localization of protons related to the onset of the nonmodulated ferroelectric phase. A quantitative analysis of low-frequency spectra provides evidence for a correlation between the anomalous increase of the damping parameter of the activated acoustic mode and the freezing of the random distribution of solitons at low temperatures.

  • Influence of bromine on the incomplete devil's staircase behavior of betaine Calcium Chloride Dihydrate
    Physical Review B, 2001
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, Filipa Pinto, A. Almeida, A Klopperpieper
    Abstract:

    the incommensurate phase are not strongly affected by bromination in contrast with what happens in the commensurate phases. It is shown that bromine weakens hydrogen bonding, preventing the localization of protons related to the onset of the nonmodulated ferroelectric phase. A quantitative analysis of low-frequency spectra provides evidence for a correlation between the anomalous increase of the damping parameter of the activated acoustic mode and the freezing of the random distribution of solitons at low temperatures.

M. R. Chaves - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic Effects of Bromine Substitution in Betaine Calcium Chloride Dihydrate
    Ferroelectrics, 2004
    Co-Authors: L. G. Vieira, J. L. Ribeiro, M. R. Chaves, M. Quilichini, Olivier Hernandez, Agostinho Almeida, A Klopperpieper
    Abstract:

    The effects of partial substitution of chlorine by bromine in incommensurate betaine Calcium Chloride di-hydrate (BCCD) have been investigated by FTIR reflectivity and elastic neutron scattering. Bromine distorts the H-bonds linking the Ca complexes and induces local symmetry breaking. The temperature dependence of b and c lattice parameters of the 4% and 8% brominated compounds reveals that this distortion has effects that are markedly anisotropic. This anisotropy may help to clarify why bromine progressively destabilizes the low temperature phases of BCCD.

  • Hydrogen bonds behaviour in brominated betaine Calcium Chloride Dihydrate
    Ferroelectrics, 2002
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, A. Almeida, Filipa Pinto, Pedro Teles, L. M. Rabkin, A Klopperpieper
    Abstract:

    The results of a comparative Raman scattering study of pure and Br - doped betaine Calcium Chloride Dihydrate (BCCD) in the 12-300 K temperature range are reported. It is shown that bromine weakens hydrogen bonding, preventing in this way the localization of protons at low temperatures. Consequently for a high enough content of bromine, the non modulated ferroelectric phase is missing.

  • On the T s Anomaly in Betaine Calcium Chloride Dihydrate (BCCD)
    Ferroelectrics, 2002
    Co-Authors: J. L. Ribeiro, M. R. Chaves, L. G. Vieira, Olivier Hernandez, A. Almeida, P. Thuery, A Klopperpieper
    Abstract:

    In this work we study the structure of the fourfold phase in a 2% brominated BCCD sample, above and below the so-called "strange anomaly" at T s , 93 K, in order to confirm the structural modification predicted by Neubert et al . on the basis of the Double Ising Spin model. The "internal transition" predicted by this model would correspond to a first order, symmetry conserving phase transition, that preserves the wavenumber of the commensurate phase and is characterized by a discontinuous increase of the symmetrized components of the structural modulation. The experimental results reported herein do not corroborate the quantitative predictions of the model.

  • influence of bromine on the incomplete devil s staircase behavior of betaine Calcium Chloride Dihydrate
    Physical Review B, 2001
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, A. Almeida, Filipa Pinto, A Klopperpieper
    Abstract:

    The results of a comparative Raman study of pure and ${\mathrm{Br}}^{\ensuremath{-}}$-doped betaine Calcium Chloride Dihydrate in the temperature interval 12--292 K are presented. The analysis of the low-frequency Raman spectra at room temperature revealed that the lowest-frequency phonons are associated with the betaines' vibrations whereas the lattice modes sensitive to ${\mathrm{Cl}}^{\ensuremath{-}}/{\mathrm{Br}}^{\ensuremath{-}}$ substitution are found above 44 ${\mathrm{cm}}^{\ensuremath{-}1}.$ The mechanisms responsible for the incommensurate phase are not strongly affected by bromination in contrast with what happens in the commensurate phases. It is shown that bromine weakens hydrogen bonding, preventing the localization of protons related to the onset of the nonmodulated ferroelectric phase. A quantitative analysis of low-frequency spectra provides evidence for a correlation between the anomalous increase of the damping parameter of the activated acoustic mode and the freezing of the random distribution of solitons at low temperatures.

  • Influence of bromine on the incomplete devil's staircase behavior of betaine Calcium Chloride Dihydrate
    Physical Review B, 2001
    Co-Authors: Yu. I. Yuzyuk, M. R. Chaves, Filipa Pinto, A. Almeida, A Klopperpieper
    Abstract:

    the incommensurate phase are not strongly affected by bromination in contrast with what happens in the commensurate phases. It is shown that bromine weakens hydrogen bonding, preventing the localization of protons related to the onset of the nonmodulated ferroelectric phase. A quantitative analysis of low-frequency spectra provides evidence for a correlation between the anomalous increase of the damping parameter of the activated acoustic mode and the freezing of the random distribution of solitons at low temperatures.

G Schaack - One of the best experts on this subject based on the ideXlab platform.

  • The Commensurate Phases of BCCD Revisited: Domain Walls, Condensates, and Quantum Effects
    Ferroelectrics, 2007
    Co-Authors: G Schaack
    Abstract:

    A new analysis of previously published experimental findings on ferroelectric (fe) BCCD (betaine Calcium Chloride Dihydrate) is presented. The commensurately (c) modulated phases, which exist in the temperature interval 46 K ≤ T ≤ 115 K at ambient pressure (sixfold, fivefold, fourfold modulated structures), display a highly anharmonic soliton regime. The domain walls separating the fe microdomains are not static but discrete, spatially localized, stable topological objects, breaking ergodicity, formed by twodimensional Bose-Einstein condensates of nonlinear, time-periodic vibrational excitations in molecular monolayers at low frequencies (≈20 cm−1), derived from the lowest optical (librational) mode of the crystal. These 2d-condensates are stacked coherently along the modulation c-axis, following the soliton wave and forming a 3-dimensional system with extreme anisotropy along c. This remarkable system is the first example, which displays strong quantum pressure effects due to quantum fluctuations, e.g. g...

  • quasi elastic light scattering in betaine Calcium Chloride Dihydrate bccd
    Journal of Physics: Condensed Matter, 1999
    Co-Authors: M Schmittlewen, G Schaack
    Abstract:

    We report measurements of the temperature (40 K T 200 K) and polarization (z(yy)x,z(xz)x) dependence of the integrated intensities of quasi-elastically scattered laser light ( = 514.5 nm) in a wavenumber interval of 0±3 cm-1 around the Rayleigh line at the different phase transitions in single crystals of BCCD. Large anomalies (central peaks) are observed at the transitions into the ferroelectric, the various commensurate (c,c´), and the incommensurate phases. The widths of the anomalies on the temperature scale are large in the regions of quasi-harmonic modulation of the structure, but narrow and distinct in the region of square-wave modulation in the solitonic phase of BCCD, where also unusual shapes on the T-axis are observed. The scattering phenomena at low temperatures are interpreted hypothetically as due to fluctuations caused by the formation or rearrangement of domain walls (solitons) in the lattice near the transitions between commensurate phases and by the variation in soliton density. The cc´ transitions are of the order-disorder type.

  • theoretical temperature electric field phase diagram for betaine Calcium Chloride Dihydrate
    Physical Review B, 1998
    Co-Authors: D G Sannikov, G Schaack
    Abstract:

    Theoretical phase diagrams for betaine Calcium Chloride Dihydrate in the presence of an external electric field are calculated. A phenomenological approach applied earlier by the present authors [J. Phys.: Condens. Matter 10, 1803 (1998)] for the construction of the temperature-pressure phase diagram, which is in agreement with the experimental diagram, is used. Expressions for thermodynamic potentials of different phases and for boundaries between these phases are given in an explicit or parametric form. The theoretical temperature-electric-field phase diagram is plotted and is compared with the experimental diagram.

  • The theoretical temperature-pressure phase diagram for betaine Calcium Chloride Dihydrate (BCCD)
    Journal of Physics: Condensed Matter, 1998
    Co-Authors: D G Sannikov, G Schaack
    Abstract:

    Theoretical phase diagrams for betaine Calcium Chloride Dihydrate are constructed. A phenomenological approach is used. Expressions for the thermodynamic potentials of different phases and for the boundaries between these phases are given in an explicit form. The theoretical temperature-pressure phase diagram is plotted and is found to be in agreement with the experimental diagram. The approximations and assumptions made in the construction of the diagrams are discussed.

  • Betaine Calcium Chloride Dihydrate (BCCD): Present status and recent experimental results>
    Ferroelectrics, 1998
    Co-Authors: G Schaack, M. Le Maire
    Abstract:

    Abstract A review of the presently available experimental information on the modulated phases of BCCD, which display a devil's-staircase behavior, is given. Some basic experimental results using methods of dielectric, high-frequency and optical spectroscopy are compiled and discussed. Data from X-ray and elastic and inelastic neutron scattering studies are also considered. This paper also includes some previously unpublished results, mainly about the role of lattice imperfections (doping, radiation-induced defects) on the sequence and stability of modulated phases and about solitons. Some problems hitherto unsolved or still under discussion are mentioned at the end of this article.

M. Quilichini - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic Effects of Bromine Substitution in Betaine Calcium Chloride Dihydrate
    Ferroelectrics, 2004
    Co-Authors: L. G. Vieira, J. L. Ribeiro, M. R. Chaves, M. Quilichini, Olivier Hernandez, Agostinho Almeida, A Klopperpieper
    Abstract:

    The effects of partial substitution of chlorine by bromine in incommensurate betaine Calcium Chloride di-hydrate (BCCD) have been investigated by FTIR reflectivity and elastic neutron scattering. Bromine distorts the H-bonds linking the Ca complexes and induces local symmetry breaking. The temperature dependence of b and c lattice parameters of the 4% and 8% brominated compounds reveals that this distortion has effects that are markedly anisotropic. This anisotropy may help to clarify why bromine progressively destabilizes the low temperature phases of BCCD.

  • on the transition to the x phase in highly brominated betaine Calcium Chloride Dihydrate bccd
    Ferroelectrics, 2000
    Co-Authors: L. G. Vieira, M. R. Chaves, M. Quilichini, J L Ribeiro, Olivier Hernandez, A. Almeida, A Klopperpieper
    Abstract:

    Abstract We report dielectric and optical birefringence measurements in 38 % brominated BCCD, which confirm the transition to the X-phase, at ambient pressure, around Tc =80 K. These results are compared with elastic neutron scattering data. A coexistence of the parent Pnma phase with the X-phase is observed in a large range of temperature centered at about Tc . It is found that the mosaic spread of the crystal varies strongly and irreversibly when a temperature cycle Pnma - X-phase - Pnma is performed. A 30% brominated BCCD has also been investigated by elastic neutron scattering. For this compound, an intermediate incommensurate phase occuring between T1 ≈ 111 K and Tc ≈50 K is observed.

  • Elastic neutron scattering and dielectric behaviour of 4% brominated betaine Calcium Chloride Dihydrate (BCCD)
    EDP Sciences, 1999
    Co-Authors: L. G. Vieira, M. R. Chaves, M. Quilichini, J L Ribeiro, O. Hernandez, A. Almeida, A Klopperpieper
    Abstract:

    We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially deuterated and x=4% brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and characterized by the coexistence of different commensurate domains (with δ = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the "harmless" low temperature part of the phase diagram, is observed up to Ti. The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks), probably with respect to a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric current measurements are in very good agreement with those obtained from neutron scattering. The dielectric anomaly observed in €''b(T) at T≈85 K, and known as the "Ts-anomaly" , could not be related with any special feature detected in the neutron data, and in particular no correlation between this anomaly and the appearance of the soliton regime can be established

  • Elastic neutron scattering and dielectric behaviour of 4% brominated betaine Calcium Chloride Dihydrate (BCCD)
    The European Physical Journal B - Condensed Matter and Complex Systems, 1999
    Co-Authors: L. G. Vieira, M. R. Chaves, A. Almeida, M. Quilichini, J L Ribeiro, O. Hernandez, A Klopperpieper
    Abstract:

    We report a combined experimental study by means of elastic neutron scattering and dielectric measurements of a partially deuterated and x =4% brominated BCCD (Betaine Calcium Chloride Dihydrate) crystal. The lowest-temperature phase is one-dimensional modulated and characterized by the coexistence of different commensurate domains (with ∂ = 1/4, 4/17, 2/9 and 1/5 on cooling), but with a clear predominance of the five-fold phase. A huge global thermal hysteresis of the wave-vector of the modulation, attaining values of about 9 K in the incommensurate phase and up to 15 K in the “harmless” low temperature part of the phase diagram, is observed up to T_i. The role of lattice defects on this phenomenon is discussed. Similarly to the behaviour of the pure compound, the structural modulation evolves on cooling towards a soliton regime (growth of third and fifth-order satellite peaks), probably with respect to a non-stabilized non-modulated ferroelectric phase. The critical temperatures deduced from dielectric constant and pyroelectric current measurements are in very good agreement with those obtained from neutron scattering. The dielectric anomaly observed in $$\varepsilon _b^(T)$$ at $$T \simeq 85$$ K, and known as the “T_s-anomaly”, could not be related with any special feature detected in the neutron data, and in particular no correlation between this anomaly and the appearance of the soliton regime can be established.

  • The role of nearest neighbour anharmonic couplings in the phase diagram of betaine Calcium Chloride Dihydrate (BCCD)
    Journal of Physics: Condensed Matter, 1999
    Co-Authors: I. Etxebarria, Jirka Hlinka, M. Quilichini
    Abstract:

    We present the results of mean-field calculations on a symmetry based semimicroscopic model for betaine Calcium Chloride Dihydrate. The model takes into account the three degrees of freedom associated with the lowest energy phonon branches as relevant variables and experimental inelastic neutron scattering data and observed transition temperatures are used to fit the coupling constants of the model potential. Although the method does not allow us to predict incommensurate phases, the results show the failure of previous models based on continuous variables to reproduce the observed phase diagram. The insertion of a new term in the model potential corresponding to anharmonic interactions between nearest neighbours is shown to be crucial to stabilize some experimentally observed commensurate phases.

Jirka Hlinka - One of the best experts on this subject based on the ideXlab platform.

  • Phonon symmetry selection rules for coherent inelastic neutron scattering: application to BCCD
    Physica B-condensed Matter, 2000
    Co-Authors: Jirka Hlinka
    Abstract:

    Abstract Recently demonstrated theorem for searching of the symmetry selection rules for coherent inelastic neutron scattering by phonons, independent of particular structural features, is applied to betaine Calcium Chloride Dihydrate (BCCD). Selection rules for the zone center phonon scattering in crystalline phases of BCCD are given explicitly.

  • Lattice dynamics of BCCD
    Ferroelectrics, 2000
    Co-Authors: Jirka Hlinka
    Abstract:

    Abstract The paper summarizes the recent studies of lattice dynamics in Betaine Calcium Chloride Dihydrate (BCCD), which are not included in the review by G. Schaack and M. Le Maire (1988). The hard harmonic mode method used previously for determination of amplitudon and pseudo-phason modes in BCCD is formulated in a general manner. It is shown why and how the well-known coupled damped harmonic oscillator model can be systematically used for determination of the bare soft mode parameters directly from a single experimental spectrum. Transmission maximum in IR spectra used previously for monitoring the modulation vector is assigned to the anti-resonance effect caused by coupling between the soft and the transverse acoustic mode.

  • The role of nearest neighbour anharmonic couplings in the phase diagram of betaine Calcium Chloride Dihydrate (BCCD)
    Journal of Physics: Condensed Matter, 1999
    Co-Authors: I. Etxebarria, Jirka Hlinka, M. Quilichini
    Abstract:

    We present the results of mean-field calculations on a symmetry based semimicroscopic model for betaine Calcium Chloride Dihydrate. The model takes into account the three degrees of freedom associated with the lowest energy phonon branches as relevant variables and experimental inelastic neutron scattering data and observed transition temperatures are used to fit the coupling constants of the model potential. Although the method does not allow us to predict incommensurate phases, the results show the failure of previous models based on continuous variables to reproduce the observed phase diagram. The insertion of a new term in the model potential corresponding to anharmonic interactions between nearest neighbours is shown to be crucial to stabilize some experimentally observed commensurate phases.

  • A Note on the Steps in Thermal Dilatation of Betaine Calcium Chloride Dihydrate.
    Journal of the Physical Society of Japan, 1998
    Co-Authors: Jirka Hlinka, Yoshihiro Ishibashi
    Abstract:

    Relative heights of the steps in the temperature dependence of thermal strain along the direction of modulation, corresponding to the phase transitions between various commensurate phases in betaine Calcium Chloride Dihydrate (BCCD), are interpreted within a simple discrete model.

  • on the t s anomaly in betaine Calcium Chloride Dihydrate
    Journal of the Physical Society of Japan, 1998
    Co-Authors: Jirka Hlinka, Yoshihiro Ishibashi
    Abstract:

    Recent experimental investigations of the dielectric anomaly inside the fourfold modulate phase of betaine Calcium Chloride Dihydrate by Le Maire et al. ( T s -anomaly) is analysed in the framework of Landau theory. Suggested symmetry for the structure is P2 1 c a (above T s ) and P1 c 1, P11 a or P2 1 11 (below T s ), respectively. It is shown that biquadratic coupling between primary order parameter with the B 2 mode (inducing the P2 1 c a to P11 a phase transition ) may provide consistent explanation of Le Maire et al. 's results.