Physical properties of hydrothermally grown gallium orthophosphate single crystals

GaPO₄ single crystals have been hydrothermally grown by the horizontal temperature gradient method. The physical properties of these single crystals were measured. The following results were obtained: lattice parametersa = 0.490 nm andc = 1.105 nm, density = 3.56 g cm^–3, Vickers hardnessH _v = 7.06 × 10⁹ Nm^–2, refractive indicesn _e = 1.611±0.006 andn ₀ = 1.599±0.006, and birefringence n = +0.012. GaPO₄ single crystals exhibited some similar properties to -quartz and AlPO₄ single crystals because of the similarity of their crystal structures.     

Structure of nylon 7 solution grown crystals

Single crystals of nylon 7 prepared by crystallization from glycerine were studied by both X-rays and electron microscopy. Electron diffraction proved that they consist of a twinned layered-structure with hydrogen bonds running parallel to their long dimension. Polyethylene decoration of such crystals showed that they are subdivided in folding domains so that both chain folding and hydrogen bonding take place along the same crystallographical planes.     

Structural studies of odd-nylon crystals grown from solution

Lamellar crystals of nylons 5, 9 and 13 in-structure were grown from solution and systematically studied by electron microscopy and X-rays. Electron diffraction showed that they all consist of a twinned structure with hydrogen bonds running parallel to the long dimension of the crystals. Polyethylene decoration of such crystals revealed folding sectorization only in the case of nylon 9. Diffraction data from films both uniaxially and biaxially oriented were used to propose a unifying model for the-structure of odd nylons based on the antiparallel model given by Tadokoro. In this model successive sheets are progressively sheared along the chain axis by approximately twice the interatomic height. Such a model is able to account well for most of the structural observations we have made on solution grown crystals.     

Growth and characterization of hexamethylenetetramine crystals grown from solution

Organic nonlinear optical single crystals of hexamethylenetetramine (HMT; 10 × 10 × 5 mm³) were prepared by crystallization from methanol solution. The grown crystals were subjected to various characterization techniques such as single crystal XRD, powder XRD, UV-Vis and electrical studies. Single crystal XRD analysis confirmed the crystalline structure of the grown crystals. Their crystalline nature was also confirmed by powder XRD technique. The optical transmittance property was identified from UV-Vis spectrum. Dielectric measurements were performed as a function of frequency at different temperatures. DC conductivity and photoconductivity studies were also carried out for the crystal. The powder second harmonic generation efficiency (SHG) of the crystal was measured using Nd:YAG laser and the efficiency was found to be two times greater than that of potassium dihydrogen phosphate (KDP).     

Physical, chemical and optical properties of aqueous L-arginine phosphate (LAP) solution

The mathematical modelling of the solution growth of high quality single crystals requires a good understanding of the fluid properties. In addition to the physical and mechanical properties a detailed knowledge of the optical parameters is required to study the dynamics of the crystal growth process. Measurements of polarizability, refractive index, optical dispersion, solubility, pH, viscosity, and density were performed on aqueous L-Arginine phosphate (LAP) solutions. The index of refraction was measured with an Abbe refractometer at four different wavelengths. Optical dispersion was calculated using the Cauchy's equation. Effects of the density and kinematic viscosity of the LAP solution are discussed in terms of the dimensionless Grashof and Reynolds number allowing a better understanding of the benefits of operating under the micro-g conditions of space for the solution growth of single crystals. The Cauchy's formula and Sellmeier formula of the refractive index have been used to determine both the gradients dn/dc and dn/dT as a function of wavelength and the polarizability of the LAP solution. The polarizability of the LAP crystal, ₂, was found to be 14.50 cm³/mol and this value was in good agreement with experimental data obtained and analyzed using the well-known Lorentz-Lorenz formula.     

Optical and microhardness studies of KDP crystals grown from aqueous solutions with organic additives

Non-linear optical (NLO) materials have acquired new significance with the advent of a large number of devices utilising solid-state laser sources. From this technological point of view, potassium dihydrogen phosphate (KDP) having superior non-linear optical properties has been exploited for variety of applications. KDP crystals were grown from aqueous solutions added with organic additives by the slow cooling method for obtaining better non-linear properties. The influence of the organic additives on the optical and mechanical properties has been studied. It has been observed that the addition of organic additives improves the mechanical strength of the crystal. It is also observed that the addition of organic additives improves the optical transmission percentage of the crystal.     

Dielectric properties of hydrothermally grown gallium orthophosphate single crystals

GaPO₄ single crystals of the low-temperature form were hydrothermally grown in 4M H₃PO₄ solution at 180 ° C. Single crystals 5.0×5.2×3.7mm³ in size could be grown in a silica glass vessel of 10 mm inner diameter. The dielectric properties of grown crystals were measured with the electric field parallel (E c) and perpendicular (E c) to thec-axis. The values of dielectric constant (ie2800-01) ofE c andE c are about 10.3 and 7.8, respectively, at frequencies from 10 kHz to 1 MHz, and these are nearly independent of frequency at room temperature. However, these values increase with temperature in the temperature range about 310 to 500 K and in the frequency region below 1 MHz. Dielectric loss (ie2800-02) increases with increasing temperature at around 300 K (E c) and 310 K (E c). From the log (conductivity) against 1/T plot in the intrinsic region at higher temperatures, the values of activation energy (E) for conduction are calculated to be about 0.17 and 0.33eV, forE c andE c, respectively.     

Physical properties of mixed crystals of alkali halides

The physical properties of mixed crystals of alkali halides are reviewed. The properties considered are experimentally determined quantities like the lattice constants, the compressibility, the elastic constants, thermal expansion, specific heats, Debye-Waller factors, dielectric constant, refractive index, IR spectra and Raman spectra and also some calculated solid-state parameters like Debye temperatures and lattice energies. A critical analysis of composition dependence shows four groups designated as follows: Type A, properties which vary linearly with composition; Type B, properties which vary slightly non-linearly with composition; Type C, properties which depend highly non-linearly on composition with the values for mixed crystals exceeding the values for end members; and Type D, properties which are peculiar to the mixed crystals and are not shown by the parent crystals. Most of the physical properties belong to Types A or B. Variation of Type C is shown only by properties affected by differences in ion size like the Debye-Waller factor and the microhardness. Properties which are symmetry-dependent like the first-order Raman spectrum and the IR spectra are of Type D. Attention is drawn to areas where further work is needed.Nomenclature a Lattice constant - A Madelung constant - Coefficient of expansion - b Repulsion constant - B Debye-Waller factor - C ₁₁ Elastic constants of a cubic crystal - C ₁₂ Elastic constants of a cubic crystal - C ₄₄ Elastic constants of a cubic crystal - d Density - Percentage difference in lattice constants - e Electron charge - Dielectric constant - H Heat of formation - K Bulk modulus - Compressibility - Reduced mass - r Interionic spacing - R Refractive index - T Temperature - Debye temperature - U Lattice energy - u Volume per molecule - V Molar volume - Wavelength     

Physical and tribological properties of diamond films grown in argoncarbon plasmas

Nanocrystalline diamond films have been deposited using a microwave plasma consisting of argon, 2–10% hydrogen and a carbon precursor such as C₆₀ or CH₄. It was found that it is possible to grow the diamond phase with both carbon precursors, although the hydrogen concentration in the plasma was 1–2 orders of magnitude lower than normally required in the absence of the argon. Auger electron spectroscopy, X-ray diffraction measurements and transmission electron microscopy indicate the films are predominantly composed of diamond. Surface roughness, as determined by atomic force microscopy and scanning electron microscopy indicate the nanocrystalline films grown in low hydrogen content plasmas are exceptionally smooth (30–50 nm rms) to thicknesses of 10 m. The smooth nanocrystalline films result in low friction coefficients (μ = 0.04–0.06) and low average wear rates as determined by ball-on-disk measurements.     

Physical properties of BeAl2O4 single crystals

Physical properties of Czochralski-grown single crystal BeAl₂O₄ are reported. Data on hardness, thermal expansion, thermal conductivity, and elastic constants are tabulated as a function of crystallographic orientation. Results indicate that the properties of BeAl₂O₄ compare favourably with those of Al₂O₃.     

Aggregation behavior of Na-neutralized styrene-ran-methacrylic acid copolymers in aqueous solution

The aggregation behavior of un-neutralized, partly and fully Na-neutralized poly(styrene-ran-methacrylic acid) copolymers in aqueous solution was investigated using a SEM technique. It was observed that the un-neutralized copolymer formed spherical particles on the Si wafer, and the average size of particles was ca. 160 nm. The particle sizes did not change much with acid content. Upon the neutralization of the acid groups of the copolymer with NaOH, the copolymer became more hydrophilic, leading to the formation of network-like feature consisting of much smaller particles (< 50 nm), compared to those of the acid copolymers. With increasing ionization, the boundary of the particles forming networks faded away, implying the formation of tubular structures.     

Unidirectional growth of pure and L-lysine added ADP crystals from aqueous solution

Pure and L-lysine added ammonium dihydrogen phosphate (ADP) crystals were grown in the 〈001〉 direction by Sankaranarayanan-Ramasamy (S-R) method. The grown crystals were characterized by X-Ray diffractometry (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR) and Vicker’s Microhardness analysis. XRD spectrum of each of the grown crystals proved its crystallinity. The crystals showed good transparency in the entire visible region. FT-IR spectra of the specimens revealed the presence of functional groups in them. The hardness of the pure and L-lysine added ADP crystals were measured and that of the added one was found higher. Meanwhile, it was found that the ADP crystals (pure and L-lysine added) grown by S-R method had higher hardness compared to ADP crystal grown by conventional method.     

Electrical and photoelectric properties of GeS layered crystals grown by different techniques

Thermally stimulated currents and anisotropic electrical conductivity are studied in GeS layered crystals prepared by the Bridgman-Stockbarger, Pizzarello, and sublimation techniques. All the crystals arep-type, regardless of the growth technique, owing to the presence of Ge vacancies. The conductivity anisotropy in the melt-grown crystals is high compared to the vapor-grown GeS. The anisotropy rises exponentially with temperature. The concentrations and ionization energies of traps in GeS crystals are determined from thermally stimulated current curves. The spectral response of the photocurrent through the crystals prepared by sublimation, whose structural perfection is higher than that of the melt-grown crystals, is governed by the spectral dependence of the absorption coefficient forad ≪ 1 (near-edge region) and by the spectral dependence of reflectivity for αd > 1 (high-α region). Regardless of the growth technique, the 293-K photocurrent spectra of GeS crystals show strongly polarized peaks at 1.65 (E ∥a) and 1.78 eV (E ∥b), which are due to the Λ ₁ ^v → Λ ₁ ^c and Δ ₂ ^v → Δ ₂ ^c optical transitions. The low-temperature photoresponse athv < 1.7 eV is due to absorption by Si impurity.     

Analysis of observations on solid-solution hardening in KBr–KCl single crystals

Available data on the temperature and concentration dependences of the critical resolved shear stress (CRSS) of KBr–KCl solid-solution crystals containing 8–41 mol% KCl in the temperature range 77–230 K have been analysed within the frame work of the kink-pair nucleation model of plastic flow in solid-solution crystals. It is found that CRSS τ decreases with the increase in temperature T in accord with the model relation ln τ = A−BT, where A and B are positive constants. The CRSS τ at a given temperature depends on solute concentration c as τ ∝ c ^p , where exponent p has a value between 0.5 and 1 depending on the temperature at which deformation is carried out. The model parameter W _o, i.e. binding energy between the edge-dislocation segment involved in the unit activation process and the solute atoms close to it (T→0 K), which is inversely proportional to B, increases with solute concentration c monotonically in accord with the model prediction W _o ∝ c ^1/4 upto a critical value c _m = 35 mol% KCl. However, W _o decreases with increase in c beyond c _m , which indicates somewhat ordered distribution of solute in the host lattice of concentrated solid-solutions with c > c _m .     

Electrical properties of zirconium diselenide single crystals grown by iodine transport method

Single crystals of zirconium diselenide (ZrSe₂) were grown by chemical vapour transport method using iodine as the transporting agent. The crystals were found to exhibit metallic behaviour in the temperature range 77–300 K and semiconducting nature in 300–443 K range. The measurements of thermoelectric power and conductivity enabled the determination of both carrier mobility and carrier concentration. The variation of carrier mobility and carrier concentration with temperature indicates the presence of deep trapping centres and their reduction with temperature in these crystals.