Guanidinium Aluminum Sulfate Hexahydrate Research Articles

The parameter of the optical indicatrix of guanidinium aluminum-sulfate hexahydrate crystals

The absorption coefficient (220–1200 nm) and refractive index (800–450 nm) spectra of a strongly anisotropic guanidinium aluminum-sulfate hexahydrate (GASH) crystals are measured. It is shown that the optical anisotropy of GASH crystals in the visible spectral region is significant, while the crystal in the polar direction becomes isotropic. The contribution of IR oscillators to the electronic polarizability of GASH is sharply anisotropic. It is found that the constants of the Sellmeier dispersion formula qualitatively agree with the vacuum ultraviolet spectra calculated from first principles. The experimental refractive indices coincide with the calculated values with an accuracy of 0.10 (n e ) and 0.1% (n o ). It is proposed to use the GASH crystal for development of optical phase difference compensators.

Calculation of the band structure and optical properties of guanidinium aluminum sulfate hexahydrate crystals

The genetic origin of a ferroelectric crystal of guanidinium aluminum sulfate hexahydrate has been established and the spectral dependences of the electron density of states, the electron energy, and the optical functions ɛ1(ħω) and ɛ2(ħω) for this crystal have been calculated in terms of the density functional theory. It has been found that there is a weak dependence of the energy of electrons in the upper valence bands on the wave vector. The calculated values of the band gap (Eg ∼ 5.44 eV) and refractive indices are in agreement with the experimental results. It has been shown that there is a strong anisotropy of the spectral band ɛ2(ħω) in the region of 6 eV, which is predominantly formed by the p states of carbon (∼60%) and nitrogen (∼40%) atoms of the C(NH2)3 group.

Inorganic structures in space groupP31m; coordinate analysis and systematic prediction of new ferroelectrics

The 62 entries listed in ICSD release 2009/1 under polar space group P31m correspond to 31 families of inorganic crystal structures, some with only one member. Coordinate analysis reveals, over a wide confidence range, 11 of these families as ferroelectric candidates. One includes the well known improper ferroelectric GASH (guanidinium aluminum sulfate hexahydrate), [(C(NH(2))(3))Al(SO(4))(2)(H(2)O)(6)], another the previously predicted ferroelectric CsNO(3) phase II. Those remaining include K(3)Nb(3)B(2)O(12), the minerals schairerite, galeite and lizardite 1T, LaNi(5)D(6) and gamma-CaNi(5)D(6.1), Ca(OCl)(2)Ca(OH)(2), [N(CH(3))(4)](2)Mo(3)S(13), Li(17)Ag(3)Sn(6) and Cs(3)As(5)O(9). Candidate selection is based upon detecting an approach by the reported atomic arrangement to the symmetry of a corresponding nonpolar supergroup. A further 13 families are typified by their reduced predictive properties, with four others likely to remain polar at higher temperatures and the remaining three noted as having a unit cell larger than reported or a misassigned space group. The primary sources of uncertainty in structurally based predictions of ferroelectricity are the reliability of the underlying structural determination and the upper limit assigned to the cationic displacement magnitudes required to achieve supergroup symmetry.

Investigations of the spin-Hamiltonian parameters and tetragonal distortion due to the Jahn–Teller effect for Cu(H 2O) 62+ clusters in C(NH 2) 3Al(SO 4) 2·6H 2O: Cu 2+ crystal

When Cu 2+ ion occupies the trigonal Al 3+ (II) site in guanidinium aluminium sulphate hexahydrate (GASH) (C(NH 2) 3Al(SO 4) 2·6H 2O) crystals, the trigonal Al(H 2O) 6 3+ octahedron in the host GASH crystal changes to the tetragonally-elongated Cu(H 2O) 6 2+ octahedron in the impurity center due to the Jahn–Teller effect. The tetragonal distortion (characterized by Δ R= R ∥– R ⊥, where R ∥ and R ⊥ represent the metal–ligand distances parallel with and perpendicular to the C 4 axis) of this Cu(H 2O) 6 2+ cluster is studied by calculating its spin-Hamiltonian parameters ( g factors g ∥, g ⊥ and hyperfine structure constants A ∥ and A ⊥) from two theoretical methods, the complete diagonalization (of energy matrix) method (CDM) and the perturbation theory method (PTM). Both methods are based on the cluster approach in which the admixture between the d orbitals of 3d n ion and the p orbitals of ligand ion is considered. The calculated results show that both methods can be used to calculate the spin-Hamiltonian parameters and to determine the structure of 3d 9 clusters in crystals. These results are discussed.

Gateless Gating Model vs. Gated Pore Model: Phase Pinning of Guanidinium Toxins in Sodium Channels

Unlike the gated pore model, which assumes the existence of a movable gate within the molecule, the gateless gating model (H. R. Leuchtag, Voltage-Sensitive Ion Channels, Springer 2008) (VSIC) explains ion-channel gating as a phase transition. Under this model, the closed channel conformation imposed by the resting electric field is a compact, ordered phase with behavior, such as critical temperature, hysteresis, fractional dispersion exponent (constant phase angle) and Curie-Weiss law, similar to that of phases seen in ferroelectric liquid crystals (VSIC, pp. 355-383). In the absence of a toxin molecule, threshold membrane depolarization indirectly brings about a stochastic phase transition to a less ordered phase in which S4 segments expand by the mutual repulsion of their positively charged residues. The resulting wider pitch of permeation pathway α helices elastically linked to the S4s permits ion replacement in the interloop H bonds and the subsequent percolation of permeant ions through the channel (VSIC, 477f, 506f). With an externally applied tetrodotoxin (TTX) or analog molecule complexed in the channel, however, the ordered phase is pinned by the toxin, inhibiting the transition to the ion-conducting phase (VSIC, 76, 382f). Phase pinning by impurities is an established effect in ferroelectric liquid crystals. In the toxin, a guanidinium group, H2N+=C(NH2)2, a highly resonant, planar, positive ion, is active in pinning the closed phase. The fact that guanidinium is also found in ferroelectric crystals such as guanidinium aluminum sulfate hexahydrate suggests that TTX enhances the spontaneous polarization of the resting phase. This explanation by the gateless gating model of specific toxin action is based on physical principles; in contrast, the phrase “TTX blocks the pore” offered by the gated pore model is vague and at the macroscopic rather than molecular scale.

Studies of EPR theory and trigonal distortion of the [Cr(H 2O) 6] 3+ cluster in ferroelectric guanidinium aluminum sulfate hexahydrate (GASH): Cr 3+ system at different temperatures

For a d 3 configuration ion, a theoretical method for studying the inter-relationships between electronic and molecular structure is investigated by diagonalizing the 120 × 120 complete energy matrices. The theoretical results show the following: (i) the local distortion structure for the Cr 3+ occupying the Al 3+ sites I and II exhibits an expansion distortion and the EPR parameters ( D, g ∥, g ⊥) are in good agreement with the experimental results at different temperatures. (ii) The | D| values decrease with the increasing temperature. (iii) The sign of the zero-field splitting parameter D is negative for the two trigonal Cr 3+ centers I and II in guanidinium aluminum sulfate hexahydrate (GASH) at 295.5, 78.45 and 1.61 K.

Wavelet Analysis in EPR Spectroscopy

Possibility of application of wavelet analysis in EPR spectroscopy is investigated. Basic mathematics of the method is summarized, with emphasis on the relation between EPR experiment and physical interpretation of wavelet transform. The fact that flrst derivative of the Lorentzian function can be used as a base wavelet is employed and the speciflc rules of the interpretation of the flnal wavelet synthesis are identifled. Analysis of a sample EPR spectrum of X-ray irradiated guanidinium aluminium sulphate hexahydrate crystal is given as an example. Set of parameters resulting from the wavelet analysis is subsequently used to reconstruct/synthesize the original EPR spectrum. The method involves an opportunity of eliminating unwanted components of the multicomponent spectra. Generally, the method may supplement other means of data analysis, in particular, in magnetic resonance.

Theoretical investigations of the spin Hamiltonian parameters for the two trigonal Cr3+ centers in GASH

The spin Hamiltonian (SH) parameters (zero-field splitting D, anisotropic g factors g∥, g⊥, the hyperfine structure constants A∥, A⊥, the nuclear quadrupole interaction constant Q′ and the effective nuclear g value gn′) for the two trigonal 53Cr3+ centers I and II in guanidinium aluminum sulfate hexahydrate are theoretically investigated by using the perturbation formulas of the SH parameters for a 3d3 ion in trigonal symmetry. According to the studies, the impurity-ligand bonding angles βi in center I (or II) are found to be about 1° (or 0.9°) smaller than the corresponding metal-ligand bonding angles βiH of the host Al3+ sites, and then the trigonal distortions for the impurity centers are also smaller than those in the hosts. The calculated SH parameters based on the above local angles are in good agreement with the observed values of EPR and ENDOR measurements. Meanwhile, the negative D values for both centers are theoretically verified. Further, the quantitative expressions are established to associate the orbital coefficients a and b in the formula of A∥ (or A⊥) with the trigonal distortion of the studied impurity centers for the first time. The validity of the results is discussed.

On the nature of the trigonal fields in hexaaquachromium(III) in guanidinium aluminum sulfate hexahydrate.

Zeeman and site selective luminescence and excitation spectra in the region of the 2E<--4A2 transition are reported for the hexaaquachromium(III) complex in the trigonal ferroelectric guanidinium aluminum sulfate hexahydrate. The two prominent transitions are due to the R1 lines of the two sites of C3 and C3v point symmetry. The two R1 lines display g parallel = -3.1 and g parallel = -3.2, respectively, and show no measurable Zeeman shift or splitting with B perpendicular c. This behavior is consistent with the presence of a very large trigonal field. A peculiar feature of the present system is the conspicuous absence of any prominent R2 line. From the Zeeman data with B perpendicular c and a comparison of vibrational sidelines in excitation and luminescence it is concluded that the R2 level strongly interacts with vibrational levels.

Electrostatic force microscopy on ferroelectric crystals in inert gas atmosphere

An electrostatic force microscope operated in inert gas atmosphere has been used to investigate the domain structure of ferroelectric crystals. The electrostatic force observed in the inert gas atmosphere is compared to that measured under ambient conditions. The domain structure of guanidinium aluminum sulfate hexahydrate has been revealed in the dynamic as well as in the static noncontact operation mode of the electrostatic force microscope. We have studied the dependence of the domain contrast on the applied external electric field in the inert gas chamber and under ambient conditions. The sign of the domain polarity could be identified in the static operation mode of our microscope. @S0163-1829~97!04601-8#

Nanoscale Visualization and Control of Ferroelectric Domains by Atomic Force Microscopy

The nanoscale visualization and control of domain structure with atomic force microscopy (AFM) in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate is reported. The origin of the domain contrast in the topographic of AFM images is explained by the piezoelectric deformation of the crystal surface in the internal electric field. The domain structure was modified by applying a voltage to the conductive AFM tip. The dynamics of domain growth has been directly observed for the first time with a resolution of 10 nm.

An electron paramagnetic resonance study of a Cu2+-doped guanidinium aluminium sulphate hexahydrate single crystal in the 3.9-433 K temperature range: Jahn-Teller effect

Detailed X-band (about 9.5 GHz) EPR studies on a Cu2+-doped C(NH2)3Al(SO4)2.6H2O single crystal have been carried out in the extended temperature range 3.9-433 K. Two magnetically inequivalent groups of Cu2+ complexes, each group consisting of three physically equivalent Cu2+ ions, were observed. The principal values of the g- and A-matrices characterizing the Cu2+ ion for one of these groups (site II) have been estimated at various temperatures, indicating a tetragonally elongated distortion of the octahedral local symmetry around the Cu2+ ions. The occurrences of static and dynamic Jahn-Teller effects below and above 423 K, respectively, have been observed.

Statics and dynamics of ferroelectric domains studied with scanning force microscopy

Scanning force microscopy for studying ferroelectric domain structures is applied. The force microscope was operated in the contact static mode (repulsive force regime) and in the noncontact dynamic mode (attractive force regime). These two techniques were applied to study cleavage faces of ferroelectric crystals of GASH (guanidinium aluminum sulfate hexahydrate) and TGS (triglycine sulfate) crystals. Using the contact mode, the positive and negative domains are revealed by opposite contrast. In the dynamic noncontact mode, the domain walls are revealed. The experimental setup allows in situ experiments to study the dynamics of ferroelectric domains. First results on the time dependence of the domains motion in TGS will be presented.

Progress in noncontact dynamic force microscopy

The technique of operating the scanning force microscope in the dynamic noncontact mode (dynamic force microscopy) has been improved. Home-built instruments based on an optical beam deflection scheme in two different environments were used. The two force microscopes were operated in ambient air and in ultrahigh vacuum, respectively. In order to control the oscillating cantilever different methods were applied: slope-detection (lock-in amplifier, RMS-to-DC converter) and frequency modulation (FM) technique as well. The advantages of this nondestructive technique are demonstrated on different samples, such as soft organic matter (hexagonally packed intermediate layer, Langmuir–Blodgett film), layer-structured compounds (CdI2), n-doped Si(111), and ferroelectric crystals [triglycine sulfate (TGS), guanidinium aluminum sulfate hexahydrate (GASH)]. On TGS and GASH cleavage faces, the ferroelectric domains and domain walls could be imaged. From experimental data a spatial resolution of about 1–2 nm in lateral and &amp;lt;0.1 nm in vertical directions could be determined.

Nanoscale Control of Ferroelectric Domain Structure by AFM

AbstractAn atomic force microscope is used for visualization and control of domain structure in the ferroelectric crystal guanidinium aluminum sulfate hexahydrate (GASH). Large built-in domains are delineated due to the tip-sample electrostatic interaction by the force microscope operating in friction mode. It is found that an applied voltage of a particular sign created new domains whereas a potential of opposite sign erased these domains. Domains created by an external electric field are visualised in topography mode due to piezoelectric deformation of the crystal. The dynamics of domain lateral growth has been directly observed with nanoscale resolution.

Surface and domain structures of ferroelectric crystals studied with scanning force microscopy

The understanding of the phenomena of ferroelectricity requires profound knowledge of the ferroelectric domain structure. In this paper we report on the progress of studying ferroelectric domains and domain walls with scanning force microscopy (SFM). Domains and domain walls of ferroelectric crystals of guanidinium aluminum sulfate hexahydrate (GASH) are imaged with SFM. Two sets of complementary results are obtained depending on the operation mode of the instrument. In the non-contact imaging mode (attractive force regime), domain walls are imaged. In the contact imaging mode (repulsive force regime) in addition to the domain wall structure, information about the polarity of the domains is obtained. In these latter images, the opposing contrast of the ferroelectric positive and negative domains is superimposed on the GASH cleavage structure. The imaging mechanism of the contact and noncontact modes are discussed. Corroborating scanning electron microscopy images are presented as well.

Superposition-model investigations of the zero-field splittings and their stress and temperature dependence for Mn 2+ in guanidinium aluminum sulfate hexahydrate

The zero-field splittings of sites I and II for Mn 2+ in guanidinium aluminum sulfate hexahydrate (GASH) are calculated from the superposition model by using the normal intrinsic parameter b̄ 2( R 0) obtained from Mn 2+ ions in many oxygen octahedra. The results are in good agreement with the experimental findings. Based on this, the local compressibilities and local thermal expansion coefficients in the vicinity of the impurity ion Mn 2+ have been studied from the stress and temperature dependence of zero-field splitting and are found to be half of the host ones. The reasonableness of these local values is discussed.

Optical properties of guanidinium aluminium sulphate hexahydrate (GASH)

Far-infrared reflection spectra were determined, for the first time, for single crystals of guanidinium aluminium sulphate hexahydrate (GASH) and its solid solution for 5 mol.% chromium isomorph (GCSH). The infrared active transversal and associated longitudinal phonon frequency and the dielectric permittivity functions for E//C and E perpendicular to C have been determined using both Kramers-Kronig analysis and a fitting procedure based on a four-parameter model. The indices of refraction were also measured using the immersion method with Cargille liquid and the results were compared with data obtained by numerical analysis of reflectivity measurements. The optical transmission of the samples were measured in the visible range and three wide energy bands were observed at about 2.6 eV, 3 eV and 4.9 eV for GASH doped with Cr, below the conduction energy zone.

Observation of ferroelectric domains in gel grown GASH

Abstract Ferroelectric crystals of guanidinium aluminum sulfate hexahydrate were grown in gel mediums. Tapered pin type crystals with hexagonal cross section were obtained. Ferroelectric domain structures on cleaved surfaces perpendicular to the spontaneous polarization were examined by scanning electron microscopy and a powder deposition technique. Sectors corresponding to crystal growth pyramids were observed in the domain structures.

Pyroelectric Imaging on the Ferroelectric GASH[C(NH2)3Al(SO4)2·6H2O

Ferroelectric domain patterms of guanidine aluminum sulfate hexahydrate (GASH) were examined by a pyroelectric probe technique, in which the laser beam scanning and data storing were controlled by a microcomputer. It was confirmed that the averaged polarity and the magnitude of pyroelectric signal on the (0001) growth region are equal to those of either (10\bar10) or (01\bar10) growth regions, which are connected by 3-fold inversion symmetry of the crystal. The standard deviation of the pyroelectric signal intensity spectrum in the (0001) region is larger than that in the other regions. The spatial fluctuation of the pyroelectric constant in the (0001) region is larger than 25 µm, which is consistent with the inhomogeneous distribution of the polar region on the spiral patterns revealed by the powder deposition technique.