Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.     

Thermal conductivity of Na<Subscript>2</Subscript>W<Subscript>2</Subscript>O<Subscript>7</Subscript> crystal

The thermal conductivity of Na₂W₂O₇ single crystal has been studied along the main crystallographic directions at temperatures of 50–573 K. A low thermal conductivity is found to correlate with a significant difference in the cation weight.     

Specific features in shaping Bi<Subscript>12</Subscript>GeO<Subscript>20</Subscript> crystals grown by low thermal gradient Czochralski technique

Germanosillenite (BGO) crystals have been grown by the low thermal gradient Czochralski technique [1] at crystallization rates of v = 0.05–4 mm/h. The evolution regularities of the faceted front forms have been studied taking into consideration their growth conditions (crystallization rate and thermal conditions). The orientations of the faces forming the crystallization front during crystal growth in the 〈111〉 direction have been determined. The relationship between the front morphology (and, therefore, growth conditions) and the quality of crystals formed is established. The quality of the BGO crystals grown is evaluated by X-ray topography.     

ESR and luminescence of ZnWO<Subscript>4</Subscript> crystals activated by gadolinium ions

The crystals of zinc tungstate (ZTO) are a radiation-hardened matrix and are widely used as scintillators for high energy radiation. Therefore, it is interesting to study the possibility of introducing gadolinium ions into this structure to obtain the lasing properties. In order to activate ZTO crystals by gadolinium ions, 0.5 mol.% of Gd₂O₃ is added to the load. High-quality large crystals of ZTO are produced. The spectra of optical transmission, luminescence excitation, and luminescence are measured at room temperature. It is shown that the introduction of gadolinium ions does not result in a shift of the main luminescence band of the ZTO crystals. The analysis of the ESR spectra and their modeling enables the calculation of spin-Hamiltonian parameters. It is shown that the observed spectrum depends on the state of Gd³⁺ ions with S = 7/2 and is well described by the spin-Hamiltonian parameters g _x = 1.9835, g _y = 1.9685, g _z = 1.9688 and D = 644.88 Gs, E = 161.49 Gs. Directions of the principal values of the D tensor are determined; they reflect a strong distortion of the nearest-neighbor oxygen environment.     

Optimization of the crystallization rate in growing Bi4Ge3O12 crystals by the LTG CZ technique

The influence of the growth rate on the shaping and quality of Bi₄Ge₃O₁₂ (BGO) crystals during their growth by the low-thermal-gradient Czochralski technique has been studied. Several series of BGO crystals have been grown with the rate varying from 0.3 to 15 mm/h. The limited growing rates at which the crystal quality is not deteriorated are established. The results of the study make it possible to increase the growth rate in commercial systems by a factor of 1.5–2 and thus significantly increase the growth efficiency.     

Comparative Analysis of Interaction Modes of Two Droplets and of a Large Population in an Aerosol Cloud

Doklady Physics - A comparative analysis of experimental results obtained by various investigators using two different experimental approaches is presented: the phenomenological approach (the...     

Characteristics of “Bounce” of Interacting Water Droplets

Technical Physics - We report on the results of experiments devoted to analysis of conditions and characteristics of “bounce” (approach and interaction through a gaseous buffer...     

Correlation of the structural imperfection and morphology of Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> crystals grown by the low-gradient Czochralski method

This paper reports on the results of investigations into the morphological structure of the facets of Bi₄Ge₃O₁₂ crystals grown by the Czochralski method under the conditions of low temperature gradient (0.1–1 K/cm). A correlation between the morphological features of the facets at the crystallization front and the formation of defects in the bulk of the crystal is revealed. It is demonstrated that the {112} facets remain regular while the growing surface deviates from the (112) crystallographic plane by an angle of up to 1°. At larger deviations, there occurs a crossover from the stable facet growth to the growth of macrosteps or normal growth depending on the growth conditions.     

Thermal conductivity and heat capacity of a ZnWO<Subscript>4</Subscript> crystal

The thermal conductivity of a ZnWO₄ single crystal in the principal crystallographic directions has been studied experimentally in the temperature range of 50–573 K, and the heat capacity of the single crystal has been measured in the range of 81–301 K.     

Thermal conductivity,heat capacity,and thermodynamic functions of the Bi<Subscript>4</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> single crystal

The thermal conductivity and the heat capacity of a single crystal of bismuth orthogermanate Bi₄Ge₃O₁₂ have been experimentally investigated in the temperature ranges 50–300 and 56–300 K, respectively. The temperature dependences of the phonon mean free path, the characteristic Debye temperature, and the changes in the entropy and enthalpy have been calculated.