Bond-charge calculation of electro-optic coefficients of diatomic crystals

A theoretical method has been set up to calculate the electrooptic tensor coefficients r(ijk), based on the Phillips-Van Vechten (PV) dielectric theory and the Levine bond charge model, Starting from the crystal structure data and only introducing the experimentally determined optical permittivity and dielectric constant, the electro-optic tensor coefficients r(ijk) can be quantitatively predicted, The theoretical calculations are in good agreement with experiment in the case of zinc blende and wurtzite crystals, For zinc blende crystals, the effects of covalent radii on the linear electro-optic coefficients are discussed. (C) 1997 Academic Press.

Fractal roughness characterization of super-ground Mn-Zn ferrite single crystals

The surface of superground Mn-Zn ferrite single crystal may be identified as a self-affine fractal in the stochastic sense. The rms roughness increased as a power of the scale from 10(2) nm to 10(6) nm with the roughness exponent alpha = 0.17 +/- 0.04, and 0.11 +/- 0.06, for grinding feed rate of 15 and 10 mu m/rev, respectively. The scaling behavior coincided with the theory prediction well used for growing self-affine surfaces in the interested region for magnetic heads performance. The rms roughnesses increased with increase in the feed rate, implying that the feed rate is a crucial grinding parameter affecting the supersmooth surface roughness in the machining process.

Nonlinearity of the complex crystals with O-H bond

A systematic and quantitative research on the structure-property correlation has been carried out in KH2PO4 (KDP), NH4H2PO4 (ADP) and HIO3, based on the dielectric theory of complex crystals and the Levine bond charge model. We, for the first time, successfully solve the problems in the calculation of the nonlinearities of the complex inorganic nonlinear optical (NLO) crystals, which have O-H bonds in their crystal structures. We do this by introducing the bond-valence equation we have set up, calculating the nonlinear optical tensor coefficients d(ijk) of these three compounds, quantitatively determining the contributions of each type of bond to the total second-order NLO tensor coefficient (d(ijk)) of the crystal, and presenting the bond parameters and the linear properties of each kind of bond. For the first time, the NLO coefficient d(36) for ADP was calculated. All calculated results are in good agreement with experimental data. We found that O-H bonds also play an important role in these crystals, except for in the important anionic groups (PO4 groups and IO3 groups). All the results thus calculated show that our method is useful in evaluating the NLO coefficients of the inorganic NLO crystals containing O-H bonds in their structures, and should be a useful tool toward the future research into new nonlinear optical materials of this kind.

SYNTHESIS AND VARIABLE-TEMPERATURE FTIR STUDY OF 5 CHIRAL LIQUID-CRYSTALS INDUCED BY INTERMOLECULAR HYDROGEN-BONDING

Five new chiral liquid crystal systems induced by intermolecular hydrogen bonding between 4-[(S)-2-chloro-3-methyl]butyroyloxy-4'-stilbazole (MBSB, proton acceptor) and 4-alkoxybenzoic acids (nBA, proton donors) were prepared. Their liquid crystalline properties were investigated by DSC and polarized optical microscopy. Chiral nematic and chiral smectic phases were observed, and the thermal stability of one complex was studied through temperature dependent infrared spectroscopy.

SYNTHESIS AND PHASE-BEHAVIOR STUDIES OF 2 NEW CHIRAL LIQUID-CRYSTALS OF SCHIFF-BASE - THE INFLUENCE OF INTRAMOLECULAR HYDROGEN-BOND ON THE PHASE-BEHAVIOR

Two new chiral liquid crystals of schiff-base type have been synthesized. This series of compounds contain a-chloro acidic ester chain prepared from commercially available L-valine. Both of the compounds exhibit tilted smectic phases; their phase transitions were studied using DSC and polarized optical microscopy; the influence of intramolecular hydrogen bonds on the phase behavior was studied as well.

SYNTHESIS OF SOME CHIRAL LIQUID-CRYSTALS AND STUDY OF THE EFFECT OF INTRAMOLECULAR HYDROGEN-BONDING ON THE PHASE-BEHAVIOR

The synthesis of three new series of chiral Schiffs bases containing benzilideneaniline and 2-hydroxybenzilideneaniline moieties as mesogenic cores is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements were used to study the phase transition temperatures and behaviour. The results reveal that most of these materials show chiral smectic mesomorphism.

SYNTHESIS OF 2 NEW HYDROGEN-BOND INDUCED LIQUID-CRYSTALS

Two new hydrogen bond induced liquid crystals with 4-butoxy benzoic acid as the proton donor and two chiral substituted stilbazole as the proton acceptor have been synthesized. Their liquid crystal transitions were studied by DSC and optical polarized microscope, the IR spectra of the complexes show the existence of the intermolecular hydrogen bond. The results of DSC and optical polarized microscope show that one of them (4BA-VSZ) has a chiral smectic C phase.

CHEMICAL-BONDS AND DIELECTRIC-CONSTANTS OF REM (RE=RARE EARTH, M=N, P, AS, SB) CRYSTALS

By using Pillips and van Vechten theory, the chemical bond parameters and dielectric constants of REM (RE=rare earth, M=N, P, As, Sb) crystals were calculated. The values calculated of dielectric constants agree with the experimental values.

SPECTRAL CHARACTERISTICS OF ER3+-ACTIVATED AND CE3+-SENSITIZED YTTRIUM-ALUMINUM-GARNET LASER CRYSTALS

We report in this paper the spectral characteristics of Er3+ (2 at.%)-activated and Ce3+ (0.3 at.%)-sensitized yttrium aluminium garnet (YAG:Er,Ce) laser crystals grown by the Czochralski technique. The absorption and emission spectra were measured at room temperature. By using absorption spectra and Judd-Ofelt theory the experimental oscillator strengths of the Er3+ transitions in the YAG:Er,Ce crystals were calculated. The energy transfer between the Er3+ and Ce3+ ions is also discussed.

CALCULATION METHOD OF LATTICE ENERGY ON COMPLEX-CRYSTALS

In this paper, based on the consideration of covalent behavior of adjacent ions in crystals, a calculation formula of lattice energy was proposed. In which, the concept of ionic effective valence and the empirical formula covalent energy were introduced,

EFFECT OF THE CONCENTRATION OF THE ER3+ ION ON THE SPECTRAL INTENSITY PARAMETERS OF ER-YAG CRYSTALS

The absorption spectra of Er:YAG (YAG, yttrium-aluminium-garnet) crystals containing different concentrations of the trivalent erbium ion were measured and the spectral intensity parameters were calculated from these experimental spectra using the Judd-Ofelt model. The results indicate that the phenomenological intensity parameters, OMEGA(lambda) (lambda = 2, 4 and 6), vary as a function of the concentration of the Er3+ ion in the Er:YAG crystal, but no variation in the fluorescence-branching ratios as a function of the concentration of the Er3+ ion is found. An empirical formula is proposed to describe the relationship between the spectral intensity parameters and the Er3+ ion concentration in the Er:YAG crystal. The spectral intensity parameters exhibit a maximum in Er:YAG crystals containing about 1-1.5 at.% Er3+ ion. The effect of the Er3+ ion concentration on the spectral intensity parameters may be attributed to the inhomogeneous lattice distortion in the cell of the Er:YAG crystal caused by the dopant erbium ions.

LUMINESCENCE AND ENERGY-TRANSFER IN GDP5O14-EU3+,SM3+ SINGLE-CRYSTALS

In this paper we report on the luminescence and energy transfer in GdP4O14:Eu3+,Sm3+ (GdPP:Eu,Sm) in single crystals grown by the hydrothermal method. The room temperature excitation, emission, absorption and IR spectra of the crystals have been measured and analysed. The energy transfer from Gd3+ and Sm3+ to Eu3+ ions in GPP:Eu,Sm crystals is also discussed.

STUDY ON GAMMA-RADIATION INDUCED LAMELLAR DAMAGE MECHANISM OF POLY(VINYLIDENE FLUORIDE)

This paper studies gamma-radiation induced lamellar damage mechanism of poly(vinylidene fluoride), using wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), electronic paramagnetic resonance (EPR) and gel fraction determination. We believe that it is ''lamellae core damage'' rather than ''lamellae surface damage'' that results in the decrease of the crystallinity.