35 research outputs found

    Crystal growth of K2TiGe3O9 in the glass

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    The kinetics and mechanism of isothermal crystal growth of K2TiGe3O9 from a glass of the same stoichiometric composition were studied. The crystal growth rate U = 1 x 10-11-1.27 x 10-10 m s-1 was experimentally determined in the temperature interval of t = 540-600Ā°C. In the range of high undercooling, Ī”t=435-375Ā°C, spherical crystals growing at (374 Ā± 19) kJ mol-1 was observed

    Far infrared properties of iron doped single crystal PbTe

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    Far infrared reflectivity spectra of single crystal PbTe samples doped with 0.2 at% Fe were measured in the temperature range between 10 K and 300 K. These spectra show very sharp and narrow dips below 120 cm-1. The experimental data were numerically analyzed using a fitting procedure based on the plasmon-phonon interaction model. Two local modes were observed. The first one was noted between 130 cm-1 and 170 cm-1 depending on the temperature and the second more frequency stable one was noted at about 230 cm-1

    Optical far infrared properties of FeS2

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    In this paper are presented the far-infrared reflectivity spectra for a cleaved FeS 2 sample measured at roam temperature and at 77 K

    Optical far infrared properties of PtSb2

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    Far infrared reflection spectra measured at room temperature were used to investigate vibrational properties of PtSb2 single crystals. The experimental results were analyzed using a dielectric function taking into account the existence of plasmonionised impurity-phonon interactions. Together with strong coupling three infrared active lattice modes at about 143, 187 and 202 cm-1 were observed. These results were discussed with respect to calculated literature vibrational frequencies. Electrical properties of single crystal PtSb2 were also measured at room temperature

    Far infrared properties of PbTe doped with Hg

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    Single crystal samples of PbTe doped with Hg were grown using the Bridgman method. Far infrared reflectivity spectra were measured at room temperature for samples with 0.5 at. % Hg; 0.9 at. % Hg and 1.4 at. % Hg. The plasma frequency decreased when PbTe was doped with Hg and it was lowest for the PbTe sample doped with 0.5 at. % Hg. The values of the determined optical free carrier mobility increased and was the highest for PbTe doped with 0.5 at. % Hg

    Far infrared properties of sintered PbTe doped with boron

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    Far infrared spectra of sintered PbTe doped with boron were analyzed. The measured infrared spectra were fitted using a modified plasmon-phonnon interaction model with two additional oscillators (at about 195 cm-1 and 285 cm-1) representing local B-impurity modes. The obtained results were compared with previously published data for a single crystal PbTe sample doped with boron

    Thermal stability and degradation of binuclear hexaaqua-bis(ethylenediamine)-(Ī¼ 2-pyromellitato)dinickel(II) tetrahydrate

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    Thermal degradation of ternary transition metal complex containing tetraanion of pyromellitic acid, pyr, and ethylenediamine, en, [Ni2(en)2(H2O)6(pyr)]Ā·4H2O, 1, was investigated under non-isothermal conditions. The mechanism of thermal degradation, which occurs in three steps, was clarified by TG/DSC measurements in conjunction with FT-IR spectroscopy and XRPD analysis. The complexity of all degradation steps has been revealed using isoconversional methods. Dehydration comprises the loss of ten water molecules in a relatively narrow temperature interval, resulting in a very complicated reaction mechanism. In addition, density functional theory calculations have been applied for better understanding of dehydration. The second degradation step, related to loss of en, was separated into two single-step processes with Fraserā€“Suzuki function. The obtained individual steps were described by Johnsonā€“Mehlā€“Avrami A2 model and Å estĆ”kā€“Berggren model, respectively. Validation of the proposed kinetic triplets for individual steps was performed using master plot and PĆ©rez-Maqueda criteria. The third degradation step is related to the fragmentation of pyr ion most likely followed with the release of a number of gaseous products

    Non-isothermal crystallization of k2o center dot tio2 center dot 3geo(2) glass

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    The crystallization of K2O center dot TiO2 center dot 3GeO(2) glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization was dominant and an activation energy of crystal growth of E-a,E-s = 327 +/- 50 kJ mol(-1) was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes gt 0.45 mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E-a,E-v = 359 +/- 64 kJ mol(-1) was calculated

    The nucleation behavior of k2o center dot tio2 center dot 3geo(2) undercooled melt

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    The nucleation of K2TiGe3O9 crystals in an undercooled melt of stoichiometric composition was studied. Volume nucleation with spherical morphology of the growing crystals was determined. The nucleation range is in the temperature interval 540-630 degrees C. A maximum of the steady state nucleation rate of I-max = 1.4 x 10(15) m(-3).s(-1) was determined at the temperature T-n(max) = 582 degrees C. The temperature and time dependence of the nucleation rate was analyzed and it was shown that such a nucleation behavior was the result of a low thermodynamic and kinetic barrier. The results showed that the temperature intervals of nucleation and crystal growth of this undercooled melt partly overlapped
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