Scanning Capacitance Microscopy of Triglycine Sulfate Crystals with the Profile Chromium Distribution

The spatial capacitance distribution, domain wall configuration, and impurity composition of triglycine sulfate TGS–TGS + Cr crystals with a growth periodic impurity structure have been investigated using scanning capacitance microscopy and X-ray fluorescence and topography. The chromium ion concentration in the strips emerging to the surface has been determined, and the periodic impurity distribution has been established. The difference between the chromium concentrations in nominally pure and impurity strips was found to be ~0.08 wt %, which is reflected in a variation in the capacitance image contrast by 0.17%. It is shown that capacitance images carry information about localization of the impurity gradient regions and domain walls and make it possible to establish a correlation between the defect and domain structures of a ferroelectric crystal.     

一种改性的TGS:Be2+热释电单晶体

本文报道了在TGS中掺入适量的金属铍离子的新晶体生长特性,晶体形貌分析,同时测定了新晶体的热释电系数(P)、介电常数(ε)、居里温度(Tc).实验表明,在TGS中掺入金属铍离子生成的TGAS:Be2+晶体的优值比明显提高.     

Growth and Kinetic Measurements of Triglycine Sulphate Crystals

Synthesis and two-step recrystallisation have been used to produce TGS basic substance. Kinetic measurements have been performed for (110)-type face on a large scale of supersaturations up to about 3%. Evidences of impurity influence for small supersaturation and the “coverage” effect has been estimated.     

Study on the Growth and Properties of Guanidine Doped Triglycine Sulfate Crystal

Guanidine doped TGS crystal is grown from the aqueous solution. The pyroelectric properties of GTGS crystal are studied, the result shows that GTGS crystal has better pyroelectric properties than those of pure TGS crystal. The effects of organic dopant on pyroelectric properties of TGS crystal are discussed.     

Dielectric Properties of Triglycine Fluoberyllate Depending on the Conditions of Growing

The paper deals with the influence of Triglycine Fluoberyllate (TGFB) monocrystals growing conditions upon the dielectric permeability ϵ and dielectric loss angle tangent tg δ in wak and strong electric fields. A temperature hysteresis of the dielectric permeability is to be observed. The Curie-temperature, the Curie-Weiss constant, the tangent of inclination angle of 1/ϵ function depending upon the temperature in ferroelectric and paraelectric regions and the values characterizing the nonlinearity of TGFB monocrystals were determined proceeding from the conditions of growing.     

Some Morphological Peculiarities of Lysozyme Crystals

Hen-egg-white lysozyme (HEWL) crystals does not differ from small molecule crystals in respect to diffusion limited growth but differ substantially as far as lattice bound strength is concerned.     

Effect of Doping and Irradiation on Optical Parameters of Triglycine Sulphate Single Crystals

Crystals of triglycine sulphate (TGS) doped with orthonitroaniline (ONA) irradiated with different doses of gamma-radiation were used to investigate gamma-radiation effect on electrical and optical parameters. The absorption coefficient and the reflectance were measured and hence the extinction coefficient, the optical refractive index and the dielectric constants (e_r′, e_r″) of unirradiated and irradiated TGS crystals were calculated. Values of the allowed indirect optical energy gap E_g^opt. of TGS doped with ONA were calculated as a function of gamma-dose. Value of E_g^opt. decreases from 4.72 eV to 4.25 eV with increasing gamma-doses from 0 up to 3 Mrad. The values of the static dielectric constant e_r(0) and the effective electrical conductivity sigma₀ at room temperature and their dependence on gamma-dose were also calculated.     

Growth of Triglycine Sulphate Single Crystals Doped by Cobalt (II) Phosphate

Modified TGS single crystals have been grown by doping with Cobalt (II) Phosphate in ferroelectric phase. The effects of different amounts of doping entities on the growth habit and P‐E hysteresis loop have been investigated. The experimental results show that while the spontaneous polarization P_s measured on variously doped crystals remains virtually unchanged, the coercive field values differ in dependence on the growth conditions and grown pyramidal features. The highest values of the coercive field E_c have been found to fall in the interval 800‐900 V/cm.     

Comparative Dielectric Investigations on Nematic Liquid Crystals with Aerosil

Dielectric measurements on a nematic room temperature mixture and the mixture with 20% aerosil were carried out. Addition of aerosil results in a small increase of the clearing temperature and in increasing relaxation frequency for the reorientation around the short molecular axis. The results are interpreted as orientation effect of the nematic sample at the fractal aerosil.     

Sb2Te3 Single Crystals Doped with Chromium Atoms

Chromium-doped Sb₂Te₃ single crystals were prepared from elements of semiconductor purity using a modified Bridgman method. The samples of these crystals were characterized by means of X-ray diffraction analysis, measurements of the reflectivity in the plasma resonance frequency range ω_p, of the Hall constant R_H and electrical conductivity σ. It was found that the incorporation of Cr atoms into the Sb₂Te₃ crystal lattice reduces the volume of the unit cell, whereas the values of ω_p and R_H (i.e. the concentration of holes) remain unaltered and the values of σ decrease with increasing chromium content. This effect is qualitatively explained by an interaction of incorporated Cr atoms with antisite defects of Sb₂Te₃ crystal lattice. The In (R_Hσ) vs. In T dependences show that the dominant mechanism of scattering of free charge carriers in the studied crystals is the scattering by acoustic phonons; the presence of chromium atoms increases the scattering rate by ionized impurities.     

Vibrational Spectra of Liquid Crystals. XII

Abstract

Recent papers by Gray et al.¹ have discussed the synthesis, structure, and properties of the mesomorphic 4-cyano, 4′-alkyl (or alkoxy) biphenyls. The reports on these materials have made mention of the existence of solid state dimorphism for certain homologs. This paper discusses this dimorphism as it manifests itself in the Raman spectrum of the octyloxy homolog (hereinafter referred to as 80CB) in the CN stretching region.

The approach used involves direct measurement of the Raman spectrum as a function of temperature, as well as computation of a correlation function obtained from the Raman band envelope by means of Fourier transformation. The application of this correlation function technique to this system has been discussed by us recently in detail.^2,3

Gray and Mosley,⁴ in a recent study of the Raman spectrum of 4-cyano, 4′-pentylbiphenyl note that the CN stretch of this compound is a doublet in the solid phase (2224 and 2233 cm^?1), but only the 2224 cm^?1 band appears in the nematic phase. They further report that only a single band appears in the CN stretching spectrum of solid 4'-heptyl-, -hexyl-, and -butyl-derivative. They speculate that the doublet might appear in the spectrum of the metastable solid phase of the heptyl homolog.

In this work, we show that for 80CB this is not the case. Rather, a doublet is observed for the stable solid but not for the metastable. The origin of this doublet is discussed, and all of the CN stretches for stable solid, metastable solid, and smectic liquid crystal are analyzed from the viewpoint of the vibrational relaxation correlation function.     

Electronic Spectra and Structure of Polydiacetylene Crystals

Abstract

The spectra of polydiacetylene crystals may be categorized such that they form two distinct classes. There are the long wavelength reflectors with their peaks of reflectivity from 15,000 to 16,000 cm^?1 and the short wavelength reflectors with their reflection peaks from 18,000 to 19,000 cm^?1. In the former set where the crystals reflect a reddish-gold color, the vibrational structure is greatly enhanced compared to the spectra for the systems of the second class which reflect in the green. X-ray crystallographic determinations have shown that in the case of the gold-reflecting crystals the polymer may be represented by an acetylenic backbone:     

Stable Liquid Crystals with Large Negative Dielectric Anisotropy - III

The synthesis of 4-n-pentyl and 4-n-butoxy derivatives of 1-(2,3-dicyano phenyl)-2-(4-(4-trans-n-pentyl cyclohexyl)phenyl) ethane and 1-(2,3-dicyano phenyl)-2-(4-trans-n-pentyl-4-trans-bicyclohexyl) ethane as well as of 1-(4-n-butoxy-2,3-dicyano phenyl) -2-(4-n-pentyl-4-biphenyl) ethane is described. These ethane derivatives as well as 4-butoxy-2,3-dicyano-4-n-pentyl p-terphenyl were all high melting and no enantiotropic or monotropic mesophases could be observed. However, they can be used as additives for photochemi-cally stable LC mixtures with low viscosity and large negative Δσ. The mesomorphic properties of some intermediate thiophene and furan derivatives are described.     

In-Plane Switching of Chiral Nematic Liquid Crystals with Different Dielectric Anisotropies

The electro-optic response in planar-aligned chiral nematic liquid crystals in an electric field oriented perpendicular to the helical structure axis is studied as a function of the magnitude and sign of the dielectric anisotropy of liquid crystal in order to understand the mechanism of this electro-optic effect. The main contribution to the electro-optic response is shown to be due to the interaction of the electric field with the dielectric anisotropy. The flexoelectric effect also contributes to the electro-optic response, but its magnitude is much smaller.     

Photoconductivity Spectra of n-type CuInSe2 Single Crystals

Photoconductivity spectra of n-type CuInSe₂ single crystals are measured in the photon energy range hv = 0.75 – 3.1 eV and as a function of temperature in the range T = 80 – 320 K. It is found that the photoconductivity of as-grown crystals is a nearly pure surface effect, while sensitization of the crystal volume is observed only after sufficiently long annealing in the presence of powdered material. To explain the temperature dependence of the photoconductivity carrier trapping processes must be taken into account.     

Sm∶YCOB晶体生长及吸收光谱表征

采用熔体提拉法生长了高质量Sm3+掺杂YCa4O(BO3)3(YCOB)晶体.通过X射线粉末衍射、高分辨X射线衍射摇摆曲线、ICP-AES、吸收光谱等对晶体的性能进行了研究.发现生长的Sm∶ YCOB晶体与YCOB晶体具有相同的结构,结晶质量较好,半高宽可达31弧秒;5at;浓度掺杂时Sm3+在YCOB晶体中分凝系数为0.773;晶体在1400～1600 nm范围内有若干较强的吸收峰.     

Microscopic Analysis of the Surface of Potassium-Ammonium Sulfate Acid Salt Crystals

Crystallography Reports - Single crystals of (K1‒x(NH4)x)3H(SO4)2 (x ≥ 0.57) solid solutions have been studied by electrical atomic force microscopy. At 296 K, the local...     

Some Novel Nematic Liquid Crystals of Negative Dielectric Anisotropy

A number of ether and ester derivatives of 1-(trans-4-n-alkylcyclohexyl)-2-(4-hydroxyphenyl)ethane bearing lateral substituents on the phenyl ring are reported. Several of the novel compounds exhibit enantiotropic nematic phases at room temperature. All of the liquid crystals described are of negative dielectric anisotropy (-0.5 -3.5). The effect of lateral substituents on the liquid crystal transition temperatures of these ethanes has been studied.     

Crystals with an Open Wave-Vector Surface: Peculiarities of Reflection and Possibilities of Designing Flat Lenses

The frequency dependence of the reflection coefficient of MgF₂ crystal in the frequency range of 200–800 cm^-1 at different orientations of the optical axis has been investigated. The experimental data are compared with the calculation results. This comparison confirms that the wave vectors for the extraordinary wave have an open surface. This makes it possible to focus a divergent beam refracted at a flat boundary ori- ented perpendicularly to the optical crystal axis. The focusing effect of a plane-parallel MgF₂ crystal plate is calculated.