Nucleation and growth of a new phase at the intermediate stage of phase transitions in metastable solutions and melts

A complete analytical solution of an integro-differential model, which describes the intermediate stage of phase transitions in one-component melts and solutions without allowance for fluctuations in the crystal growth rates, is found. An exact analytical solution of the kinetic equation is determined within the framework of this model. The density of distribution function of crystals in sizes is found. An integro-differential equation for the system metastability level (for its supercooling/supersaturation) is derived for different kinetic mechanisms of particle nucleation. A complete analytical solution of this equation is constructed on the basis of saddle-point method for the Laplace-type integral (steepest descent method). Four approximations of the analytical solution are analyzed and its convergence is shown. The kinetic mechanisms of Weber-Volmer-Frenkel-ZePdovich and A loirs are studied. A transient behavior of the number of particles and the mean crystal size is determined for supercooled melts

Thermal Non-Destructive Testing of Zirconium Composite Coatings

Cylindrical samples made of zirconium with a composite coating based on yttrium, aluminum, titanium and silicon oxides were studied by thermal testing. The dependence of the radiation temperature of equally heated objects on the characteristics of these coatings was established

Spectroscopic properties of HoFe3(BO3)4, NdFe3(BO3)4 and Ho0.75Nd0.25Fe3(BO3)4 single crystals

Polarized absorption spectra of ferroborates HoFe3(BO3)4, NdFe3(BO3)4 and Ho0.75Nd0.25Fe3(BO3)4 were measured at room temperature in spectral range 4000–24500 cm−1 (400–2500 nm). The studied single crystals were grown from solution-melts. Intensities of the f-f transitions were measured and the Judd–Ofelt parameters Ωλ of Ho3+ and Nd3+ ions in the studied crystals were calculated. It was revealed that the crystals content not strongly influences the Judd–Ofelt parameters. The Ω2 parameter for Ho3+ ion is the most sensitive to the crystal content. Linear dichroism of the hypersensitive transitions appeared to be the largest one for both rare earth ions

Influence of magnetic ordering on electronic structure of Tb 3+ ion in TbFe 3(BO 3) 4 crystal

Optical absorption spectra of trigonal crystal TbFe 3(BO 3) 4 have been studied in the region of 7 F6 → 5 D4 transition in Tb 3+  ion depending on temperature (2–220 K) and on magnetic field (0–60 kOe). Splitting of the Tb 3+ excited states, both under the influence of the external magnetic field and effective exchange field of the Fe-sublattice, have been determined. Landé factors of the excited states have been found. Stepwise splitting of one of the absorption lines has been discovered in the region of the Fe-sublattice magnetic ordering temperature. This is shown to be due to the abrupt change of equilibrium geometry of the local Tb 3+  ion environment only in the excited state of the Tb 3+  ion. In general, the magnetic ordering is accompanied by temperature variations of the Tb 3+ local environment in the excited states. The crystal field splitting components have been identified. In particular, it has been shown that the ground state (in D 3 symmetry approximation) consists of two close singlet states of A 1 and A 2 type, which are split and magnetized by effective exchange field of the Fe-sublattice. Orientations of magnetic moments of the excited electronic states relative to that of the ground state have been experimentally determined in the magnetically ordered state of the crystal. A pronounced shift of one of absorption lines has been observed in the vicinity of the TbFe 3(BO 3) 4 structural phase transition. The temperature interval of coexistence of the phases is about 3 K. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011

Spectroscopic properties of Nd3+ in orthorhombic δ-BiB3O6 crystal

Absorption spectra of the Nd3+ ions in an orthorhombic δ-BiB3O6 single crystal were measured in the spectral range 11,000-20,500 cm−1. The f-f transition intensities were analyzed in terms of the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω2 = 6.35 × 10−20 cm2, Ω4 = 4.86 × 10−20 cm2, and Ω6 = 11.233 × 10−20 cm2. The strengths, spontaneous emission probabilities, branching ratios, spectroscopic quality factor and excited state radiative lifetime were calculated for laser transitions from the 4F3/2 state to 4IJ manifold. Spectroscopicproperties of Nd3+:δ-BiB3O6crystal favor lasing at 1.3 μm, where this crystal possesses near non-critical phase matching for second harmonic generation

Spectroscopic properties of Nd3+ in orthorhombic δ-BiB3O6 crystal

International audienceAbsorption spectra of the Nd3+ ions in an orthorhombic δ-BiB3O6 single crystal were measured in the spectral range 11,000-20,500 cm−1. The f-f transition intensities were analyzed in terms of the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω2 = 6.35 × 10−20 cm2, Ω4 = 4.86 × 10−20 cm2, and Ω6 = 11.233 × 10−20 cm2. The strengths, spontaneous emission probabilities, branching ratios, spectroscopic quality factor and excited state radiative lifetime were calculated for laser transitions from the 4F3/2 state to 4IJ manifold. Spectroscopicproperties of Nd3+:δ-BiB3O6crystal favor lasing at 1.3 μm, where this crystal possesses near non-critical phase matching for second harmonic generation