Effect of uniaxial stress on the birefringence of triglycine sulphate crystals doped with L threonine

The temperature and spectral dependences of the birefringence ??n _i of triglycine sulphate (TGS) crystals with L-threonine impurity have been investigated. Doping with L-threonine is found to reduce the temperature dependence of ??n _i of TGS crystals. The baric coefficients of shift of the phase-transition (PT) point, ?T _c /???m, are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping. The temperature and spectral dependences of the combined piezoelectric constants ?? _im ⁰ have been calculated. The stepwise changes in all piezoelectric constants at the PT of doped crystals are found to be much smaller than those for pure crystals.     

The use of photoinduced light scattering for the evaluation of photoelectric fields in Lithium Niobate Crystals

The photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown from the melt with 58.6 mol % of Li₂O (LiNbO₃ stoich), in the nominally pure single crystals of congruent composition (LiNbO₃), and in congruent single crystals doped with Cu²⁺, Zn²⁺, and Gd³⁺ are found from the parameters of the photoinduced light scattering indicatrix obtained with the use of a 60-mW He-Ne laser.     

Inter-relationship between optical dielectric constant and interatomic separation of mixed crystals in ionic and covalent binary compound families

An ion dependent dielectric model is developed for mixed binary crystals. The interatomic separation (R) and optical dielectric constant (ε_∞) of the mixed crystals are computed from the measured values of R and ε_∞ of pure crystals. An empirical relation between ε_∞ and R is therefore found for mixed crystals by using the computed values. It is found that the dielectric behaviour of ionic mixed crystals is cation dependent while that of covalent mixed crystals is anion dependent. The prescribed theory can therefore be used to form different mixed crystals with particular values of ε_∞ required in any specific opto-electronic devices.     

Characterization of pure and copper-doped iron tartrate crystals grown in silica gel

Single crystal growth of pure and copper-doped iron tartrate crystals bearing composition Cu _x Fe_(1???x)C₄H₄O₆·nH₂O, where x = 0, 0.07, 0.06, 0.05, 0.04, 0.03, is achieved using gel technique. The elemental analysis has been done using energy-dispersive X-ray analysis (EDAX) spectrum. The characterization studies such as Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), magnetic analysis and thermal analysis have been done for crystals with x = 0 for pure iron tartrate and with x = 0.05 for copper-mixed iron tartrate crystals. A detailed comparison has been made between pure and doped crystals.     

Iminodiacetic acid doped ferroelectric triglycine sulphate crystal: Crystal growth and characterization

Single crystals of iminodiacetic acid (HN(CH₂COOH)₂) doped triglycine sulphate (IDATGS) crystals have been grown from aqueous solution containing 1-10 mol% of iminodiacetic acid at constant temperature by slow evaporation technique. The effects of different amounts of doping entities on the growth habit have been investigated. X-ray powder diffraction pattern for pure and doped TGS was collected to determine the lattice parameters. The grown crystals were subjected to Fourier transform infrared (FTIR) spectroscopy studies to find the presence of various functional groups qualitatively. The dielectric permittivity has been studied as a function of temperature. An increase in the transition temperature (49.2-49.7 °C) of IDATGS crystals is observed. The dielectric constant (ε′_max) of IDATGS crystals vary in the range 922-2410 compared to pure TGS (T_c=49.12 °C and ε′_max=3050). Curie Weiss constants C_p and C_f in the paraelectric and ferroelectric phases were determined. The transition temperature (T_c) is found to decrease with increase in dopant concentration. P-E hysteresis studies show the presence of internal bias field in the crystal. Piezoelectric measurements were also carried out at room temperature. Domain patterns on b-cut plates were observed using scanning electron microscope. The micro hardness studies reveal that the doped crystals are harder than the pure TGS crystals. The low dielectric constant, higher transition temperature, internal bias field and hardness suggest that IDATGS crystals could be a potential material for IR detectors.     

Growth and comparison of physicochemical properties of pure,Ca and Sr doped NH4Sb3F10 single crystals for electro optic applications

Single crystals of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ are grown by slow evaporation technique. The effect of dopants on the growth and physicochemical properties also have been investigated and reported for the first time. The grown crystals are characterized with the aid of single crystal X-ray diffractometry to confirm the crystal structure. EDAX studies are done to confirm the presence of dopants in the crystal lattice. The vibrational frequencies of various group ligands in the crystals have been derived from the Fourier transform infrared (FT-IR) spectrum. From the optical absorption spectrum the band gap energy was calculated and it was found to be 5.76, 6.29 and 6.35 eV for pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals respectively. Thermal stability of the sample has been analysed using TG-DTA analysis. The activation energy of pure, Ca²⁺ and Sr²⁺ doped NH₄Sb₃F₁₀ crystals were calculated from the dc conductivity measurements and it is found to be 0.2728, 0.2816 and 0.3622 eV Experimental results shows improved physicochemical properties when the dopant is added to the pure material.     

The effect of Fe doping in Potassium Hydrogen Phthalate single crystals on structural and optical properties

This work investigates the influence of iron doping on Potassium Hydrogen Phthalate (KHP) single crystals by the slow evaporation solution growth technique. Factors such as evaporation rate, solution pH, solute concentration, super saturation limit, etc. are very important in order to have optically transparent single crystals. As part of the work, the effects of metallic salt FeCl₃ in different concentrations were analyzed with pure KHP. Powder X-ray diffraction suggests that the grown crystals are crystallized in the orthorhombic structure. The functional groups and the effect of moisture on the doped crystals can be analyzed with the help of a FTIR spectrum. The pure and doped KHP single crystal shows good transparency in the entire visible region, which is suitable for optical device applications.The refractive indices along b axis of pure and doped KHP single crystals were analyzed by the prism coupling technique. The emission of green light with the use of a Nd:YAG laser (λ=1064 nm) confirmed the second harmonic generation properties of the grown crystals.     

Dielectric properties of glycine phosphite crystals in the model of a phase transition with inclusion of high-order invariants

Dielectric anomalies in the vicinity of the ferroelectric phase transition in nominally pure glycine phosphite (GPI) crystals and glycine phosphite crystals containing 2 mol % glycine phosphate (GP) are studied. It is revealed that the impurity-induced internal macroscopic polarization observed for GPI-GP crystals brings about smearing of the dielectric anomalies in directions both parallel and perpendicular to the axis of spontaneous polarization. The ferroelectric phase of the GPI and GPI-GP crystals is characterized by an unusual variation in the inverse permittivity in the Z direction perpendicular to the Y axis of spontaneous polarization. The temperature dependence of the inverse permittivity is described by a power expression (T _c ? T) ⁿ with an exponent n larger than unity. The experimental data are analyzed in terms of the proposed thermodynamic model with two order parameters, namely, the displacement parameter η and the order-disorder parameter P, which have different physical natures but the same symmetry and allow for coupling invariants of the ηP and η³ P types, as well as for the built-in polarization in the case of GPI-GP crystals. The experimental and theoretical dependences are in good agreement. The coefficients of bilinear and nonlinear coupling between the order parameters are determined. It is shown that the phase transition in the crystals occurs in the vicinity of the tricritical point and that the unusual behavior of the permittivity with a variation in the temperature is explained by the contribution from high-order invariants of coupling.     

Measurement of nonlinear refractive index of pure and doped KTP crystals by Z-scan technique using cw He–Ne Laser

Single crystals of pure, Mo and W doped KTP crystals were grown by flux technique. The grown crystals were subjected to various characterization studies such as EDX, powder XRD, FTIR and UV analysis. The SHG efficiencies of the pure and doped KTP crystals were measured by Kurtz–Perry technique and it was found that the doped KTP crystals exhibit higher values of SHG. Nonlinear refractive indexes were measured on different growth planes of pure and doped crystals by Z-scan method using a cw (continuous wave) He–Ne laser at 632.8 nm. The measured values of nonlinear refraction of different planes were in the order of 10⁻¹² cm²/W.     

Temperature dependence of the spin-lattice relaxation time for quadrupole nuclei under conditions of NMR line saturation

The contributions of different mechanisms of nuclear spin-lattice relaxation are experimentally separated for ⁶⁹Ga and ⁷¹Ga nuclei in GaAs crystals (nominally pure and doped with copper and chromium), ²³Na nuclei in a nominally pure NaCl crystal, and ²⁷Al nuclei in nominally pure and lightly chromium-doped Al₂O₃ crystals in the temperature range 80–300 K. The contribution of impurities to spin-lattice relaxation is separated under the condition of additional stationary saturation of the nuclear magnetic resonance (NMR) line in magnetic and electric resonance fields. It is demonstrated that, upon suppression of the impurity mechanism of spin-lattice relaxation, the temperature dependence of the spin-lattice relaxation time T₁ for GaAs and NaCl crystals is described within the model of two-phonon Raman processes in the Debye approximation, whereas the temperature dependence of T₁ for corundum crystals deviates from the theoretical curve for relaxation due to the spin-phonon interaction.     

Growth and characterization of a pure and doped nonlinear optical l-histidine acetate single crystals

Single crystals of pure, Cu²⁺and Mg²⁺ doped l-histidine acetate (LHA) were grown successfully by slow evaporation technique. The X-ray diffraction (XRD) studies were carried out for the pure and doped grown crystals. Absorption of these grown crystals was analyzed using UV-vis-NIR studies, and it was found that these crystals possess minimum absorption from 200 nm to 1500 nm. The pure and doped crystals are characterized by Fourier transform Raman (FT-Raman), thermal and photoconductivity studies. Vickers microhardness tests were carried out for the pure and doped crystals and the mechanical strengths were found. The dielectric constant and the dielectric loss with frequency were also studied.     

Growth and characterization of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals

Single crystals of pure and potassium iodide (KI)-doped zinc tris-thiourea sulphate (ZTS) were grown from aqueous solutions by the slow evaporation method. The grown crystals were transparent. The lattice parameters of the grown crystals were determined by the single-crystal X-ray diffraction technique. The grown crystals were also characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. The FT-IR spectrum was recorded in the range 400-4500 cm⁻¹. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) studies reveal that the materials have good thermal stability. Atomic absorption studies confirm the presence of dopant in ZTS crystals. The electrical measurements were made in the frequency range 10²-10⁶ Hz and in the temperature range 40-130 °C along a-, b- and c-directions of the grown crystals. The present study shows that the electrical parameters viz. dc conductivity, dielectric constant, dielectric loss factor and ac conductivity increase with increase in temperature. Activation energy values were also determined for the ac conduction process in grown crystals. The dc conductivity, dielectric constant, dielectric loss factor and ac conductivity of KI-doped ZTS crystal were found to be more than those of pure ZTS crystals.     

Synthesis,growth and studies of undoped and sodium chloride-doped Zinc Tris-thiourea Sulphate (ZTS) single crystals

Single crystals of undoped (pure) and sodium chloride (NaCl)-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. Morphological alterations have been observed when NaCl is doped into ZTS crystals. Density of the grown crystals was measured by floatation method. The values of unit cell parameters from single crystal X-ray diffraction (XRD) studies show that pure and sodium chloride-doped ZTS crystals are in orthorhombic structure. Impurity concentration in the doped crystals was estimated by using an atomic absorption spectrometer. Second Harmonic Generation (SHG) test for the undoped and NaCl-doped ZTS crystals was performed by the powder technique of Kurtz and Perry using a pulsed Nd:YAG laser. Microhardness studies show that hardness number (H_v) increases with load for all the grown crystals of this work. From the values of work hardening coefficients, it is concluded that pure and sodium chloride-doped ZTS crystals belong to the category of soft materials. UV–vis–NIR spectra show that the grown crystals have wide optical transparency in the entire visible region. Birefringence studies of the grown samples have been performed by channelled spectrum method. The thermal stability of the materials is found to be increasing with the doping concentration of sodium chloride (NaCl) in the lattice of ZTS crystals.     

Conversion of broadband thermal radiation in lithium niobate crystals of various compositions

The conversion of the broadband thermal radiation in stoichiometric (R = 1) lithium niobate single crystals that are grown from melt with 58.6 mol % of LiO₂, congruent (R = Li/Nb = 0.946) melt with the K₂O flux admixture (4.5 and 6.0 wt %), and congruent melt and in congruent single crystals doped with the Zn²⁺, Gd³⁺, and Er³⁺ cations is studied. It is demonstrated that the conversion efficiency of the stoichiometric crystal that is grown from the melt with 58.6 mol % of LiO₂ is less than the conversion efficiency of congruent crystal. In addition, the stoichiometric and almost stoichiometric crystals and the doped congruent crystals exhibit the blue shift of the peak conversion intensity in comparison with a nominally pure congruent crystal. For the congruent crystals, the conversion intensities peak at 520 and 495 nm, respectively.     

Domain structure of triglycine sulfate family crystals according to the data of piezoresponse force microscopy and their macroscopic dielectric properties

The domain structure of triglycine sulfate (TGS) crystals, specifically nominally pure crystals and those with impurities (LADTGS+ADP, DTSG, and TGS:Cr), is studied by piezoresponse force microscopy (PFM). The measured macroscopic dielectric characteristics are compared with microscopic data on the domain structure of these crystals. The values of the spontaneous polarization, bias voltage, and dielectric permeability as a function of temperature ?(T) are shown to be in agreement with the PFM data. The anomalous behavior of the dependence ?(T) was observed for LADTGS+ADP crystals.     

Messungen der Dielektrizitätskonstanten von reinem und NH4F-dotiertem Eis

The dielectric constant of pure and NH₄F doped ice single crystals has been measured at temperatures around — 10°C in the frequency range between 0.07 and 500 kc/s. The values measured on pure ice are in agreement with the Debye theory. At frequencies around 0.1 kc/s the dielectric constant?′ of doped crystals is higher than that of pure ice. Treating the frequency as a parameter, the dielectric constant?′ goes through a maximum and a minimum with rising NH₄F concentration. No dependence of the Debye dispersion frequency on the doping concentration could be detected.     

Luminescence and ionic conductivity of bariumfluorochloride

The luminescence and ionic conductivity of pure and doped BaFCl crystals are reported. The ionic conductivity occurs mainly via chloride ion vacancies, whereas the efficient, yellow luminescence is ascribed to oxygen impurities (O′_F).     

Superconducting energy gap in Bi2Sr2Ca2Cu3O10+δ (Bi2223) single crystals

Current-voltage characteristics of S-I-S tunnel break junctions fabricated from pure undoped Bi2223 single crystals (T _c =110 K) were measured. High quality of the crystals enabled production of good tunnel junctions with a low or almost zero leakage current and well developed gap structure in the tunneling spectra. The peak-to-peak energy gap values 2Δ_p-p in different crystals and the tunnel junctions ranged from 80 to 105 meV. The tunneling conductance in the superconducting state was normalized to that in the normal state and compared to a smeared BCS density of states. A simple fit of the data gave the average value of Δ=38.5 meV and reduced gap 2Δ/kT _c ?8, consistent with a very strong coupling mechanism.     

Refractometry of uniaxially compressed triglycine sulphate crystals doped with L-valine

The temperature and spectral dependences of the refractive indices n _i of triglycine sulphate (TGS) crystals doped with L-valine have been investigated. Doping is found to weaken the temperature dependence of n _i of TGS crystals. The electronic polarizabilities ?? _i , refractions R _i , and parameters of UV oscillators (??_0i , B _1i ) of mechanically distorted doped TGS crystals have been calculated. The temperature coefficients of the shift of the phase-transition point, ?T _c /??? _m , are found to be somewhat smaller than those for pure TGS crystals, which is confirmed by the increase in the hardness of TGS crystals after doping.     

Structural physical regularities of the mechanism and kinetics of the formation of piezoelectric and ferroelectric crystals from a liquid phase

The specific features of the kinetics of formation of noncentrosymmetric crystals from electrolyte solutions are investigated for approximately 50 salts of M-N electrolytes. The “solubility product-limiting solution supercooling” set {SP-ΔT _m } for noncentrosymmetric crystals is separated into nine characteristic taxons in which the regularities of formation and growth of crystals are revealed and compared. It is demonstrated that the minimum supercoolings ΔT _m are observed for solutions of crystals with weak “acentric” properties. Higher supercoolings ΔT _m are observed for solutions of noncentrosymmetric crystals that belong to potential ferroelastics and exhibit pronounced acentric properties. The proposed taxonomy of electrolytes makes it possible to predict the conditions for the growth of perfect crystals for fundamental and applied physics.