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Paper reports the second harmonic generation (SHG) in ferroelectric AgNa(NO2)2 crystals being driven by the spontaneous and electric field induced polarizations. Obtained results are interpreted within the phenomenological theory which considers the free energy describing the interaction between the spontaneous or electric field induced polarizations and spatially inhomogeneous electric polarizations resulted from propagating optical waves. Relatively high magnitudes of the effective second order nonlinear optical (NLO) susceptibilities in these crystals are combined with several phase matching geometries which allows to consider them as high-performance materials for potential NLO applications, such as parametric generation and amplification, frequency doubling, or other applications that require high-efficient frequency conversion. In addition, an anomalously large response of NLO susceptibilities with respect to an applied electric field has been found in the vicinity of the Curie point. This may also have a number of applications, especially in those devices where an efficient tunable control of SHG intensity is demanded. [ABSTRACT FROM AUTHOR]

One of the simplest quantum many-body systems is the spin-1/2 Heisenberg antiferromagnetic chain, a linear array of interacting magnetic moments. Its exact ground state is a macroscopic singlet entangling all spins in the chain. Its elementary excitations, called spinons, are fractional spin-1/2 quasiparticles created and detected in pairs by neutron scattering. Theoretical predictions show that two-spinon states exhaust only 71% of the spectral weight and higher-order spinon states, yet to be experimentally located, are predicted to participate in the remaining. Here, by accurate absolute normalization of our inelastic neutron scattering data on a spin-1/2 Heisenberg antiferromagnetic chain compound, we account for the full spectral weight to within 99(8)%. Our data thus establish and quantify the existence of higher-order spinon states. The observation that, within error bars, the experimental line shape resembles a rescaled two-spinon one with similar boundaries allows us to develop a simple picture for understanding multi-spinon excitations. [ABSTRACT FROM AUTHOR]

Abstract: The present work reports an experimental investigation on the influence of glycine (NH2CH2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH3)3NCH2COO·H3AsO4. The dielectric dispersion (20Hz<ν<3MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130K

Temperature dependences of the dielectric permittivity of betaine phosphite crystals are studied both without and under application of an electric bias. It is shown that, in view of the fact that the high-temperature improper ferroelastic (antiferrodistorsive) phase transition at T[sub c1] = 355 K is nearly tricritical, the nonlinear temperature dependence of inverse dielectric permittivity in the paraelectric phase and the effect of the field on the dielectric permittivity can be described within a phenomenological model containing two coupled (polar and nonpolar) order parameters with a negative coupling coefficient. An analysis of the model revealed that, in the case where two phase transitions, a nonpolar and a ferroelectric one, can occur in the crystal, all of its dielectric properties, including the polarization response in a field, can be described by one dimensionless parameter a. For the crystal under study, we have a = -2.5. This value of the parameter corresponds to a second-order ferroelectric transition far from the tricritical point, at which a = -1. It is shown that the polarization response in the paraelectric phase in an electric field calculated within this model differs radically from that in the ferroelectric phase-transition model for which the Curie-Weiss law holds in the paraelectric phase. [ABSTRACT FROM AUTHOR]

We demonstrate the second harmonic generation (SHG) in ferroelectric AgNa(NO2)2 crystals resulting from the spontaneous and electric field induced polarizations. Relatively high effective nonlinear optic (NLO) susceptibility is combined in this crystals with the existing several phase matching geometries of NLO interaction. Anomalously large response of SHG with respect to an applied electric field has been found in the vicinity of the paraelectric-to-ferroelectric phase transition. The behavior of NLO properties in the ferroelectric phase and especially in the region of the Curie point is discussed within the phenomenological theory. [ABSTRACT FROM AUTHOR]

We have attempted to understand the low temperature microscopic structure and dipolar ordering of the (BP)x(BA)1 -x mixed system in a previous work, by performing detailed pyroelectric, dielectric and polarization reversal measurements, complemented with Raman and infrared spectroscopic investigations. Whenever the same experimental techniques are used, our experimental results agree extremely well with those reported in the literature. However, our use of slightly different methods disclosed new aspects of the phase sequence, which allowed us to trace an alternative phase diagram for the (BP)x(BA)1-x mixed system. The present paper is aimed at emphasising the most relevant of these previous results. Particular attention will be paid to the role of ferro-antiferroelectric competitions in the mixed system (BP)x(BA)1 -x. [ABSTRACT FROM AUTHOR]

In this work we present a detailed study of the temperature evolution (290 K–20 K) of the polarized Raman spectra in a single crystal of glycinium phosphite. The phase transition manifests itself by the activation of new Raman bands and by the occurrence of anomalies in the temperature dependence of the wavenumber of some external and internal modes. The results show that occurring deformations in molecular units contribute relevantly to the spontaneous polarization in GPI. The anomalous behaviour of the wavenumber and of the damping constant of some bands is in good agreement with a theoretical model based in a pseudospin-phonon interaction. [ABSTRACT FROM AUTHOR]

Betaine calcium perchlorate monohydrate (here designate by BCPM) is a new compound of the amino acid betaine with a triclinic symmetry and with the space group P..., at room temperature. In this work we present a detailed study of dielectric properties and of Raman scattering spectra of BCPM, which disclose interesting structural changes in the temperature range 20 K-300 K. [ABSTRACT FROM AUTHOR]

The mixed system of betaine arsenate and betaine phosphate (BP)x(BA)1-x displays, at low temperatures, dielectric anomalies that have been tentatively associated to re-entrant glass phases. In this work, we report results obtained for the composition x = 0.52. The temperature dependence of the complex dielectric constant, polarization hysteresis loops and pyroelectric currents reported prove that an effective ergodicity breaking occurs in the antiferroelectric phase and show that this phase is destabilized at low temperatures. There is also evidence for a high internal bias field, in the whole temperature range studied. Infrared and Raman spectroscopy indicate that the various dielectric anomalies observed reflect structural transformations. [ABSTRACT FROM AUTHOR]

In this work we present a detailed study of the temperature dependence (35 K- 290 K) of the Raman spectra in a single crystal of betaine phosphite. A softening of a relaxational mode is observed above and below the para-ferroelectric phase transition at Tc2 ∼ 213 K, which appears to have its primary origin in the different internal dynamic deformations and reorientations of molecular units. Our results suggest the existence of a certain degree of local disorder between 110 K and 170 K. [ABSTRACT FROM AUTHOR]

Betaine arsenate (BA) and betaine phosphate (BP) are addition compounds of the amino acid betaine [(CH 3 ) 3 N + CH 2 COO - ] and arsenic and phosphoric acids, respectively. The mixed system (BP) x (BA) 1 - x displays, at low temperatures, dielectric anomalies that have been interpreted as due to additional transitions to re-entrant glass phases originated by frustrated FE and AF interactions. In this work, Raman and infrared spectroscopic data are analysed and compared with results of complex dielectric constant, pyroelectric measurements performed during thermal cycles under different bias electric fields and low frequency polarization hysteresis loops. The results obtained for the x = 0.75 composition do not give any evidence for the stabilisation of a re-entrant glass phase or a non-ergodic regime, and a long-range order seems to prevail in the whole temperature range studied. The inclusion of BA is however capable of destabilising the AF order, giving rise to a slightly polar ferroelectric phase at low temperatures. Moreover spectroscopic results reveal that methyl groups of the betaine molecules act as excellent probes for the detailed study of the phase transition sequence in this system. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Betaine potassium bromide dihydrate: (CH 3 ) 3 N + CH 2 COO - ·KBr·2H 2 O, for short BKBr, is a compound of the aminoacid betaine with an orthorhombic symmetry and the space group Pbcm at room temperature. The study of the dielectric properties of this compound, in the temperature range 20-300K, provides a clear evidence for the existence of a structural phase transition occurring around 160K. This phase transition is related to the freezing of water molecules degrees of freedom. [ABSTRACT FROM AUTHOR]

Studies the structures of the high- and low-temperature phases of 38 percent brominated betaine (trimethylammonioacetate) calcium chloride dihydrate or the X-phase by single-crystal neutron diffraction. Symmetry of the X-phase; Anti-symmetric displacements of the betaine molecules.

A study is reported of acoustic anomalies in the vicinity of the antiferrodistortive and ferroelectric phase transitions in nominally pure betaine phosphite crystals and a crystal with 3% betaine phosphate impurity. The observed anomalies in the velocity and damping rate of longitudinal acoustic waves propagating along different crystallographic axes are interpreted within Landau theory. It is shown that the phase transitions in these crystals are characterized by a relatively weak correlation of the order parameter to strain and by a considerable contribution to the acoustic anomalies of an interaction higher in order than striction. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]