The study of the influence of γ-irradiation on LiF crystals by optical,electrical and mechanical characteristics

The influence of the dose of γ-irradiation on some physical properties (storage of colour centres, ionic conductivity, microhardness) in LiF crystals differing in oxygen content is studied. It is found out that optical, electrical and mechanical characteristics change nonmonotonously with an increase in dose of γ-irradiation in the range from 10⁴ to 10⁷ J per kg. Maxima and minima are revealed on all the three dependencies, indicating a periodie construction and redistribution of radiation defects during the change of the absorbed dose. Oxygen impurity enhanced the colouring of LiF crystals, significantly reduced the conductivity, caused mechanical softening and intensified the secondary radiation processes having qualitatively changed the behaviour of electrical and mechanical properties with an increase in irradiation dose.     

The influence of γ-irradiation on ferroelectric and polarization properties of TGS crystals

The experimental investigation of pyroelectric and polarization properties of TGS crystals was made. TGS crystals were grown under constant growth conditions (temperature and supersaturation of the solution) and γ-irradiated in a wide range of irradiation. The influence of γ-irradiation on the quality parameter M₂ of crystals, on the form of hysteresis loops, on size of spontaneous polarization and shifting field was ascertained.     

Effect of γ-radiation on mechanically processed MgO powder (compressive and shear stress)

In mechanically processed MgO samples, γ-irradiation results in the formation of F⁺ and V⁻ centres. The higher the mechanically induced degree of distortion of the samples, the higher the concentration of F⁺ centres obtained by the irradiation. Our experiments suggest that the irradiation can be used as a probe in determining the concentration of the mechanically induced vacant anion and cation sites.     

Absorption band at 7.6 eV induced by γ-irradiation in silica glasses

Optical absorption of defects induced by γ-irradiation in both natural and synthetic silica is experimentally investigated in the vacuum-ultraviolet (UV) range. Our results show that γ-rays, in a dose range of 1000 Mrad, induce an absorption band centered at 7.6 eV, the so-called E band, whose growth kinetics is not related to γ-activated precursors but to defects of the glassy matrix directly induced via the breaking of Si–O bonds occurring under γ-irradiation. Moreover, we observe that γ-rays do not bleach the E band present in some silica samples before irradiation, so ruling out that the associated defects can be precursors of the paramagnetic E^′ centers, also induced by γ-irradiation.     

Effect of Terminal Groups on Formation of Crystal Structure in α,γ-Disubstituted n-Alkanes

The crystal and molecular structure of 1,16-dibromohexadecane have been determined by X-ray diffraction. Crystal data; empirical formula, C₁₆H₃₂Br₂, formula weight M_r = 384.24, monoclinic, P2₁/a, a = 31.00(2), b = 5.38(1), c = 5.48(1) Å, β = 90.8(2)°, V = 914(3) ų, Z = 2, D_x = 1.396 g/cm³, δ(CuKα) = 1.5418 Å, μ(CuKα) = 55.41 cm⁻¹, F(000) = 396.00, T = 293 ± 1 K, wR = 0.082, R = 0.054 for 940 unique reflections [I > 3.00σ(I)]. The molecular skeleton has an all trans zigzag hydrocarbon chain. The crystal has a layer structure, but the directions of molecular axes in neighbouring layers alternate. This molecular packing resembles to that of 1,16-hexadecanediol, whereas n-alkanes or α-monosubstituted n-alkanes do not appreciably have these molecular arrangement. The effect of terminal groups at both ends of α,ω-disubstituted n-alkanes on the crystal structure is discussed.     

Band gap of triglycine selenate,triglycine fluorine beryllate,triglycine sulfate and its variation under γ-irradiation

The band gap for three ferroelectrics (triglycine selenate, triglycine fluorine berryllate and triglycine sulfate) is determined using an optic method. A shift of self-absorption edge towards longer wave lengths is observed when exposed to irradiation by γ rays with a dosage of ∽ (2 ÷ 7) · 10⁷ r as well as corresponding decrease of band gap. The observed changes are connected with the chemical nature of the studied substances.     

Effect of Cyclic Stress Reduction on the Creep Behaviour of Al‐Ag and Al‐Ag‐Zr Alloys Containing γ′ and γ Precipitates

Creep tests under the effect of cyclic stress reduction were conducted to Al‐16 wt%Ag and Al‐16 wt%Ag‐0.1 wt%Zr alloys aged at 548 and 673 K. The steady state creep rate was found to be higher under cyclic stress reduction condition than that under static creep condition for the same maximum stress. An expression for the temperature dependence of the threshold stress for cyclic creep acceleration is offered. Cyclic creep acceleration is interpreted using the dislocation cross‐slip model. TEM investigations confirmed that the addition of Zr to Al‐Ag alloy accelerates the formation and coarsening of γ′ and γ‐phases. The mean value of activation energy for both alloys aged at 548 K was found to be 35±0.3 kJ/mol, and 58±0.4 kJ/mol for alloys aged at 673 K.     

Zur Kristallographie der martensitischen ε → α-Gitterumwandlung

Many iron and cobalt alloys transform to the martensitic reaction γ → ε → α. The platelets of the hex. ε-martensite are very thin. Thus the growth of the crystals is limited in the direction [0001]_ε and the transformation ε → α can be treated as a plane problem. Metallographic investigations demonstrated the size, form and orientation of the α-crystals after cooling without and with external tension. On the basis of connection of the hex. and the bcc. lattice formulae are discussed of the directions of the lattices, and the changes of the volume and the shape, resp.     

Fabrication of CdS nanorods in inverse microemulsion using HEC as a template by a convenient γ-irradiation technique

Cadmium sulfide (CdS) nanocrystals were successfully prepared in inverse microemulsion under γ-irradiation at room temperature. Their shape can be controlled by changing the surfactant concentrations and the addition of hydroxyethyl cellulose (HEC) as the template. CdS nanorods were successfully obtained under γ-irradiation using HEC as the template, which was confirmed by the observation of transmission electron microscopy (TEM). Without the addition of HEC, spherical CdS crystals were formed. X-ray powder diffraction (XRD) pattern and electron diffraction (ED) analysis showed the hexagonal lattice of CdS in the nanorods. Additionally, the optical properties of CdS nanorods were characterized by ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy.     

Effect of γ-irradiation on the lattice parameter and colour centre concentration in pure Ca2+, Sr2+ and Eu2+ doped KCI crystals

The changes of lattice parameter and colour centre concentration are examined in KCI crystals (both pure and Me²⁺-doped) irradiated by γ-rays at room temperature. For the pure crystals the relative volume change vs. F-centre concentration plot reveals the presence of two stages, one ascribed to the introduction of colour centre pairs (or F centres only) and other to the generation of the new dislocations (or new dislocations with trapped-hole centres). In Me²⁺ doped crystals the lattice expansion bears a complex character (in the initial irradiation stage a transient maximum appears). Additional anomaly appears in Eu²⁺ KCI in the high-dose range where in spite of a distinct F-centre concentration drop a marked raise of the lattice parameter is observed.     

The effect of impurities on the β → α transformation process in tin

This article presents data on the impurities influencing the β → α transformation of high purity tin (99.9995%): temperature of the α → β transition-T₀, nucleation and α-crystal growth.     

The crystal and molecular structure of 5α,8α-epidioxyergosta-6,22-dien-3β-acetate

From the mushroom species Tricholoma populinum LANGE which shows interesting pharmaceutical effects the steroid 5α,8α-epidioxyergosta-6,22-dien-3β-ol has been isolated. The acetate of this compound crystallizes in the monoclinic space group P 2₁ with two molecules in the unit cell of dimensions a = 19.788, b = 7.241, c = 9.914 Å, β = 103,97°. The final R-value is 0.079 for 1082 reflections.     

Crystal and Molecular Structure of 6α-Methyl-3,20-Dioxo-5β-Pregnan-17α-yl Acetate

The title compound 6α-methyl-3.20-dioxo-5β-pregnan-17α-yl acetate crystallizes in the monoclinic space group P 2₁ with two molecules in the unit cell and the lattice parameters a = 10.889, b = 11.056, c = 9.8029 Å, β = 101.51° The crystal structure is isostructural with medroxyprogesterone acetate and refined by full matrix least squares calculations up to the discrepancy factor R = 0.051.     

Mechanism of nucleation and growth of crystals under α → β transformation of tin

This article presents data on the mechanism underlying the nucleation and growth of α-Sn crystals in mono- and polycrystal β-Sn tin. It is demonstrated that the low temperature deformation and thermocycling (subjection to the cyclic changes of temperature) of the samples of tin (99.9995% Sn) brings to the increase in the α-Sn crystal nuclestion rate. Kinetics of the nucleation is characterised by the presence of the non-steady State period t_n. On analysing the temperature dependencies of the rate of the α-Sn centre growth obtained for the planes (100), (001) and (110) it was shown that the mechanism of movement of the interphase boundary depends on the value of the motive force ΔF.     

The Morphology of Some Hydrothermally Synthesized Li-Minerals: A-Zeolite, α-Eucryptite, β-Spodumene and β-Eucryptite

The hydrothermal treatment of glass with the composition 2 LiF, Al₂O₃, 3 SiO₂ at 1 kbar in the range of 150 °C to 850 °C gave rise to the formation of A-zeolite with orthorhombic unit cell with å = 10.31 Å/b̊ = 8.18 Å/c̊ = 5.0 Å (space group Pna2₁), α-eucryptite, trigonal, å = 13.4 Å/bº = 13.4/Å/cº = 9.0 Å (space group R 3 ), β-spodumene, pseudocubic/tetragonal, å = 7.53 Å/b̊ = 7.53 Å/c̊ = 9.15 Å (space group P4₃2₁2), β-eucryptite, monoclinic, å = 7.75 Å/b̊ = 5.2 Å/c̊ = 11.16 Å (space group P6₂22). The morphology and development of the mineral phases depend on the temperature of formation.     

The Molecular and Crystal Structure of 3β-O-(2′,3′ -O-isoropylidene-α-L-rhamnopyranosyl) — digitoxigenin

3β-O-(2′,3′ -O-isoropylidene-α-L-rhamnopyranosyl) — digitoxigenin crystallizes in the monoclinic space group P 2₁ with two molecules C₃₂H₄₈O₈ per unit cell and the lattice constants a = 7.865, b = 6.470, c = 29.803 Å, β = 93.95°. The structure was solved by direct methods of phases determination and subsequently refined by least squares technique to the final R-value 0.06. The position of the lactone ring is disordered in the crystal.     

A study of the influence of short-range order,clustering and crystal lattice defects on positron annihilation in α and α + β brass

A theoretical model is proposed allowing the consideration of the influence of local neighbourhood of an atom on the positron density enhancement at one or another type of atom in a binary alloy. With the help of this model the direction of the change of angular correlation peak height caused by appearance of short range order or clustering can be predicted. Cu–Zn-alloys containing 5.4, 15, and 37 weight % Zn are investigated. The peak height of samples quenched from 300°C. show a weak minimum at 90°C. This seems not to be caused by the increase of short-range order but rather by a process of clustering. probably by segregation of Zn atoms at stacking faults and dislocations. The observed recovery of plastically deformed brass can be well explained by annealing out of vacancies and following recrystallization, where the α + β brass shows characteristic deformation induced properties. Peak height measurements of recovery of crystal lattice defects in binary alloys seems to be only weakly influenced by effects such as short-range order or tendency of clustering. The formation energy of monovacancies in Cu-37 wt% Zn is determined to be (0.81 ± 0.02) eV.     

On the coexistence of phases at the α–β transition in quartz

The character of the α–β transition in crystals of natural and synthetic quartz has been studied by measuring the refractive index. The coexistence of two different crystallographic modifications over some temperature range has been established. The α–β phase transition is supposed to be attributed to the near-critical phase transitions. In synthetic quartz with Al and Fe structural impurity the α–β transition consists of two successive transitions. First the transition from the α-phase to an intermediate one takes place, then the intermediate phase is transformed into the β-Phase. Within a certain temperature range there exists only the intermediate phase.