Growth,optical, mechanical,dielectric and theoretical properties of picolinium maleate NLO single crystal

Nonlinear optical single crystals of picolinium maleate (PM) were grown by slow evaporation method. The grown crystal was subjected to single crystal X-ray diffraction analysis to confirm that the crystal belongs to the monoclinic crystal structure with space group P2₁/c. The optical transmission range of the grown crystal was measured by UV–Vis–NIR region with the lower cut-off wavelength as 330 nm. The optical bandgap is found to be 3.75 eV. Mechanical strength of the grown crystal was analyzed using Vickers microhardness tester. Dielectric constant and dielectric loss of picolinium maleate are measured in the frequency range from 50 Hz to 5 MHz at different temperatures. Further, electronic properties, such as valence electron plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal have been estimated.     

Studies on the optical and dielectric properties of a zinc thiourea chloride NLO single crystal

Single crystals of a nonlinear optical material, zinc thiourea chloride were grown by the slow evaporation technique. The crystal structure and lattice parameters of the grown crystal were determined by the single crystal X-ray diffraction studies. The single crystal XRD revealed that the material crystallized in a orthorhombic crystal system. Optical studies were carried out and it was found that the tendency of transmission observed from the specimen, with respect to the wavelength of light, is practically more suitable for opto-electronic applications. The optical band gap is found to be 4.30 eV. Optical constants such as the band gap, refractive index, reflectance, extinction coefficient and real (?_r) and imaginary (?_i) components of the dielectric constant and electric susceptibility were determined from the UV–vis–NIR spectrum. The dielectric constant and dielectric loss of zinc thiourea chloride were measured in the different frequency range from 50 Hz to 5 MHz at different temperatures. Further, electronic properties, such as valence electron plasma energy, Penn gap, Fermi energy and electronic polarizability of the grown crystal have been estimated.     

Growth and characterization of novel ferroelectric bis(methylammonium) tetrachlorozincate

Single crystals of ferroelectric bis(methylammonium) tetrachlorozincate are grown by slow evaporation method within a period of 5 weeks at 303 K. The grown crystal is subjected to single crystal X-ray diffraction, UV-vis analysis, Fourier transform infrared spectroscopy (FTIR) and mechanical and thermal analysis (TG/DTA/DSC). The crystalline perfection is identified with HR XRD studies. Two phase transitions at about 208.2 and 285.3 °C are identified from differential scanning calorimetric studies. The results are confirmed with differential thermal analysis and dielectric studies. The band gap energy is calculated from UV studies as 2.7 eV. Important parameters like polarizability which are useful for device fabrication, are also calculated theoretically using Clausius-Mossotti equation and Penn analysis and their results are compared.     

Evaluation of the second order strain derivatives of the electronic dielectric constant of alkali halides

We have evaluated the second order strain derivatives of the electronic dielectric constant of alkali halides employing two different theories viz. the Clausius—Mossotti theory of polarizability and the Penn model of energy gap. The results obtained from the two theories are in fair agreement with each other. It has been emphasised that the present calculations can be used to separate the electronic and ionic contributions to the second order strain derivative of the static dielectric constant.     

Band structure and optical properties of antimony-sulfobromide: density functional calculation

The electronic structure, linear, and non-linear optical properties of ferroelectric-semiconductor SbSBr are investigated in the non-polar (paraelectric) and polar (ferroelectric) phase, using the density functional methods in the generalized gradient approximation. The electronic band structure obtained shows that SbSBr has an indirect forbidden gap of 2.16 and 2.21 eV in the paraelectric and ferroelectric phase, respectively. The linear photon-energy dependent dielectric functions and some optical functions, such as absorption and extinction coefficients, refractive index, energy-loss function, reflectivity, and optical conductivity in both phases and photon-energy dependent second-order susceptibilities in the ferroelectric phase are calculated. Moreover, some important optical parameters, such as the effective number of valence electrons and the effective optical dielectric constant, are calculated in both phases.      

BaZr0.5Ti0.5O3电子结构、力学和光学性质的第一性原理研究

在广义梯度近似（GGA）下,采用基于密度泛函理论的第一性原理方法对BaZr0.5Ti0.5O3的电子结构、力学性质和光学性质进行了理论计算．计算得到该晶体的晶格常数为4.145925 Å,且此材料是一种间隙的半导体材料,价带和导带都来源于Ba原子、O原子的p态和Ti原子、Zr原子的d态电子间的杂化;力学性质的计算得到：BaZrO3和BaZr0.5Ti0.5O3的晶体结构稳定,且BaZrO3晶体掺杂Ti元素后体系的硬度变大;光学计算结果表明BaZr0.5Ti0.5O3的静态介电常数为4.20,吸收主要集中在低能区,静态折射率为2.00,能量损失峰出现在11.59eV处．上述研究结果为BaZr0.5Ti0.5O3材料的设计和应用提供了理论依据．     

BaZr0.5Ti0.5O3电子结构、力学和光学性质的第一性原理研究

在广义梯度近似（GGA）下,采用基于密度泛函理论的第一性原理方法对BaZr0.5Ti0.5O3的电子结构、力学性质和光学性质进行了理论计算．计算得到该晶体的晶格常数为4.145925 Å,且此材料是一种间隙的半导体材料,价带和导带都来源于Ba原子、O原子的p态和Ti原子、Zr原子的d态电子间的杂化;力学性质的计算得到：BaZrO3和BaZr0.5Ti0.5O3的晶体结构稳定,且BaZrO3晶体掺杂Ti元素后体系的硬度变大;光学计算结果表明BaZr0.5Ti0.5O3的静态介电常数为4.20,吸收主要集中在低能区,静态折射率为2.00,能量损失峰出现在11.59eV处．上述研究结果为BaZr0.5Ti0.5O3材料的设计和应用提供了理论依据．     

Optical, thermal, dielectric and ferroelectric behaviour of sodium acid phthalate (SAP) single crystals

Sodium acid phthalate (SAP), an efficient semi-organic crystal having dimensions 17×8×2 mm³ has been grown from aqueous solution by slow evaporation technique at room temperature within the period of 2 weeks. The lattice parameters of the grown crystals were determined using single-crystal X-ray diffraction analysis. The presence of functional groups was estimated qualitatively by Fourier transform infrared (FTIR) analysis. The band gap energy was determined using optical absorption studies. The TG/DTA analysis reveals that the SAP crystal is thermally stable up to 141.6 °C. The dielectric constant and dielectric loss was studied as a function of frequency and the corresponding activation energy (E_a) has been calculated for the grown crystal. Scanning electron microscope studies enunciate the ferroelectric domain patterns of the SAP crystal. Ferroelectric property of the grown crystal was confirmed by hysteresis loop studies.     

氧化锌掺钡的电子结构及其铁电性能研究

运用基于密度泛函理论的第一性原理方法计算了不同原子百分比含量的Ba掺杂Zn0半导体体材料超晶胞的能带结构、电子态密度、极化率和相对介电值.计算结果表明:Ba掺杂的Zn0体系为直接带隙半导体材料,其禁带宽度随着Ba原子掺杂百分比的增加呈现出逐渐增大的趋势.体系铁电性能的计算表明:与纯Zn0相比,Zn0掺入Ba原子后的极化率与相对介电值发生了较为明显的变化,其极化率随着Ba原子掺杂百分比的增加而增大,相对介电值随着Ba原子掺杂百分比的增加而减小.对角化后的极化率分量的数值结果表明:在电场作用下超胞中可能存在微畴结构,并且由于畴间电偶极矩的强相互作用,使得超胞宏观上表现为几乎具有各向同性的极化率特征.     

Calculation of electronic ion polarizability and parameters of interionic repulsion in LiNbO3 crystals

A method for calculating the anisotropy of the electronic polarizability of O^2? ions in oxygen octahedral ferroelectrics has been proposed. It is shown that, in the case of mixed ion-covalent bonds in the crystal, the calculation of the polarizability within the approximation of isolated ions gives incorrect results. The principal components of the polarizability tensor for the O^2? ions and the electronic polarizability of the Nb⁵⁺ ions are calculated for the LiNbO₃ ferroelectric. Analysis of the stability of the LiNbO₃ structure confirms the results obtained.     

Ab initio calculations of the elastic, electronic, optical, and vibrational properties of PdGa compound under pressure

The structural, elastic, electronic, optical, and vibrational properties of cubic PdGa compound are investigated using the norm-conserving pseudopotentials within the local density approximation (LDA) in the framework of the density functional theory. The calculated lattice constant has been compared with the experimental value and has been found to be in good agreement with experimental data. The obtained electronic band structures show that PdGa compound has no band gap. The second-order elastic constants have been calculated, and the other related quantities such as the Young’s modulus, shear modulus, Poisson’s ratio, anisotropy factor, sound velocities, and Debye temperature have also been estimated. Our calculated results of elastic constants show that this compound is mechanically stable. Furthermore, the real and imaginary parts of the dielectric function and the optical constants such as the electron energy-loss function, the optical dielectric constant and the effective number of electrons per unit cell are calculated and presented in the study. The phonon dispersion curves are also derived using the direct method.     

Synthesis,optical, dielectric,thermal and mechanical properties of a nonlinear optical amino acid crystal: Bis-glycine hydrobromide

A semi organic material Bis-glycine hydrobromide (C₄H₁₁N₂O₄⁺Br⁻) has been synthesized by slow solvent evaporation technique. The grown crystal was subjected to single crystal X-ray diffraction studies and its crystal parameters were confirmed. The FTIR analysis confirms the presence of various functional groups present in the title compound. The Kurtz powder second harmonic generation test shows that the crystal is a potential candidate for optical second harmonic generation. The UV–vis spectrum reveals the transparency of the crystal and enumerates the direct band gap energy of the material. The dielectric constant and the dielectric loss were studied as a function of frequency. The thermal studies indicate that the material is thermally stable up to 290 °C. The hardness number was calculated to be 110 kg/mm² from the Vicker's microhardness test.     

Synthesis,spectral, thermal,optical and dielectric studies on 4-dimethylaminopyridinium picrate crystals

Single crystal of 4-dimethylaminopyridinium picrate was grown by slow evaporation solution growth method. The optical properties of the crystal were studied by using UV–vis absorption and transmittance studies. The emission spectrum indicates that the crystal shows green and red fluorescence emissions. The band gap energy of the crystal was calculated and it is found to be 2.05 eV. The thermal stability of the crystal was studied using thermogravimetry-differential thermal (TG-DTA) analyses. The thermal anomalies observed in the differential scanning calorimetry (DSC) heating and cooling cycles indicate the occurrence of a first order phase transition. FTIR spectrum was used to confirm the presence of various functional groups in the crystal. The synthesized crystal shows SHG efficiency 32 times greater than that of potassium dihydrogen phosphate (KDP). The dielectric constant and dielectric loss of the crystal decreases with increases in frequency.     

Studies on second harmonic generation efficiency of organic material l-arginine maleate dihydrate

A crystalline organic nonlinear optical l-arginine maleate dihydrate has been grown by solution growth technique. Single crystal X-ray diffraction study confirms that the grown crystal belongs to triclinic system having non-centrosymmetric space group P₁. The optical studies were carried out to estimate the transmission range, band gap, extinction coefficient, refractive index and reflectance of the grown crystal. The fundamental solid state parameters were determined from dielectric studies to analyze the polarizability and second harmonic generation efficiency of the grown crystal. Activation energy of the grown crystal was found to be 0.218 eV from ac conductivity measurements.     

Ga掺杂ZnS的电子结构和光学性质

本文基于第一性原理平面波赝势（PWP）和广义梯度近似（GGA）方法,对ZnS闪锌矿结构掺入杂质Ga体系进行结构优化处理. 计算了该体系下ZnS材料的电子结构和光学性质. 详细分析了其平衡晶格常数、能带结构、电子态密度分布和光学性质．结果表明：由于杂质Ga的引入,ZnS体系体积略有膨胀,并在在费米面附近出现了深施主能级,单纯的通过Ga掺杂来实现低阻ｎ型ZnS材料较为困难;由于杂质能级的引入,整个介电峰向低能方向偏移,电子在可见光区的跃迁显著增强．     

Growth,spectral, optical,and dielectric studies on novel semiorganic NLO single crystal: d-phenylglycine hydrochloride

Good quality novel semiorganic nonlinear optical single crystal of d-phenylglycine hydrochloride has been grown from the aqueous solution by low temperature solution growth method. X-ray diffraction reveals that the crystal crystallises into orthorhombic system with noncentrosymmetric space group P2₁2₁2₁. Experimental parameters are evaluated based on single-crystal XRD and the calculated values of the polarisability were compared with the values of polarisability using Clausius–Mossotti equation. The functional groups present in the grown crystal were confirmed by Fourier transform infrared spectral analysis. The ¹H and ¹³C FT–NMR has been recorded to elucidate the molecular structure. Ultraviolet–visible-near infra-red absorption studies on this crystal reveal that the minimum absorption region is around 228 nm. The optical band gap of the crystal was found to be 2.9 eV. The scanning electron microscope study has been carried out to determine the surface morphology of the grown crystal. Photoluminescence studies show that the material emits violet fluorescence. Thermal studies bring forth that the crystal is thermally stable up to 255 °C. Dielectric studies reveal that both the dielectric constant and dielectric loss decrease with the increase in frequency as like the typical semiorganic nonlinear optical crystals such as bisthiourea zinc chloride, bisthiourea cadmium chloride and l-arginine dihydrogen phosphate. Electrical conductivity measurements were carried out and the Arrhenius plot is used to determine the value of activation energy. The Kurtz powder analysis on the crystal confirms the existence of second harmonic generation properties. The SHG efficiency was found to be 1.15 times that of KDP crystal.     

Ga掺杂ZnS的电子结构和光学性质简

本文基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对ZnS闪锌矿结构掺入杂质Ga体系进行结构优化处理.计算了该体系下ZnS材料的电子结构和光学性质.详细分析了其平衡晶格常数、能带结构、电子态密度分布和光学性质.结果表明:由于杂质Ga的引入,ZnS体系体积略有膨胀,并在费米面附近出现了深施主能级,单纯的通过Ga掺杂来实现低阻n型ZnS材料较为困难;由于杂质能级的引入,整个介电峰向低能方向偏移,电子在可见光区的跃迁显著增强.     

Electronic structure and optical properties of Mg_xZn_(1-x)S bulk crystal using first-principles calculations

We perform the first-principles calculations within the framework of density functional theory to determine the elec- tronic structure and optical properties of MgxZnl-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZnl_xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZnl-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant compo- sition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZnl_xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.     

Dielectric and anharmonic behaviour of mixed alkali halides

Summary In the present paper an analysis of the dielectric behaviour and anharmonic contribution to the dielectric constants has been made of KCl−KBr mixed ionic crystals. The temperature and volume derivatives of static (ε₀), electronic (ε_∞) dielectric constants and energy gap parameter (E _g) have been calculated using the Szigeti and Havinga and Bosman dielectric theories. The anharmonic contributions have been estimated in terms of temperature derivatives of dielectric constants at constant volumes. The modified form of Clausius-Mossotti theory of dielectric polarization has been used for the mixed crystal under study. The calculated quantities have been compared with the available experimental data. A good agreement has been obtained. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

Good quality single crystals of pure and metal ion (Ni²⁺) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni²⁺doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni²⁺doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.