2 results
Optimization of gettering processes of metallurgical-grade silicon for solar cell applications
- Inna M. Iskandarova, Igor P. Zvyagin, Andrey Knizhnik, Andrey V. Konovalov, Boris Potapkin, Natalya Arutyunyan, Alexander I. Zaitsev, Thomas McNulty, Timothy Sommerer, Mohamed Rahmane, Victor Lou, Stanislav Soloviev, Alexei Vert, Svetlana Selezneva
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1210 / 2009
- Published online by Cambridge University Press:
- 31 January 2011, 1210-Q08-21
- Print publication:
- 2009
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- Article
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Conversion efficiency of a solar energy in the electric is substantially determined not only by the total impurity concentration in solar cell element, but also by impurity chemical and physical state. Gettering processes, which are included in the technology of solar cell manufacturing, are usually used for such impurity redistribution. In order to optimize gettering processes we developed a program tool based on the fundamental physical and chemical laws. The description of physical and chemical behaviour of impurities in silicon is based both on known experimental data, and on calculations of necessary parameters by means of present-day thermodynamic and quantum-chemical methods. Developed tool helps to choose a gettering regime (a temperature profile, time, getter layer thickness) for optimization of these processes for the given initial chemical composition of the silicon wafer. Possibility of analysis of recombination activity of various types of defects in silicon on the basis of carrier lifetime criterion allows to obtain an estimation of efficiency of the gettering processes. Using this program tool we demonstrated that solar cell efficiency can be significantly increased by optimal choice of gettering conditions.
Study of Pyrochlore and Garnet-based Matrices for Actinide Wastes Produced by a Self-propagating High-temperature Synthesis
- Sergey V. Yudintsev, Tatiana S. Ioudintseva, Andrey V. Mokhov, Boris S. Nikonov, Eduard E. Konovalov, Sergey A. Perevalov, Sergey V. Stefanovsky, Alexander G. Ptashkin, Eduard M. Glagovsky, Alexander V. Kouprine
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- Journal:
- MRS Online Proceedings Library Archive / Volume 807 / 2003
- Published online by Cambridge University Press:
- 01 February 2011, 273
- Print publication:
- 2003
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- Article
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Actinide-containing wastes are among the most dangerous for the environment. Such waste streams originate from reprocessing operations with irradiated nuclear fuel and conversion of weapons-grade plutonium metal into dioxide. The long-term toxicity of actinides derives from the presence of isotopes with half-life varying from hundreds of years (Am241) to tens of thousands (Pu239) or even millions of years (Np237). Therefore, these waste fractions need to be incorporated into durable crystalline host phases. The matrices have to incorporate substantial amounts of actinides, and possess chemical durability and resistance to radiation damage. Complex oxides with fluorite-derived and garnet lattices meet these requirements. Self-propagating high-temperature synthesis (SHS) based on exothermic oxidizing-reduction reactions may be used for production of these waste forms. This technology has the following advantages: absence of extrinsic heating sources, low energy requirements for equipment, high reaction velocity, simplicity of design of processing equipment, feasibility of remote-handling the processes, and lack of considerable amounts of facility decommission wastes. The basic features of the SHS technology are as follows: duration of initiation is 0.05–5.0 sec, temperature in a combustion wave is within 1500–3000 °K, and the velocity of advance of the combustion wave is 1–150 mm/s. Two sets of samples composed of pyrochlore and garnet-type phases were produced with SHS. The first of them corresponds to nominal pyrochlore formulation Y2Ti2O7 doped with various amounts of actinides: 10–30 wt.% UO2, 10 wt % PuO2, 10 wt % NpO2, or 9.5 wt % UO2 + 0.5 wt % Am2O3. The precursor was prepared from oxides of the base phases (TiO2, Y2O3, AnO2), an oxidizer (MoO3), and Ti. In the second set of runs, the target phase was garnet (Y2.8Gd0.2)(Al4.7Ga0.3)O12, where Gd3+ was used as a surrogate for Am3+. The initial batches were composed of MoO3, Y2O3, Gd2O3, Al2O3, Ga2O3, and metallic Al. Phase compositions of the samples have been determined by XRD and SEM/EDS. Samples of the first series are composed of major pyrochlore with minor metallic Mo. The samples with 10 wt % actinides do not contain any separate actinide oxide phase. In the samples with 20 and 30 % UO2 a separate uranium oxide phase was observed. SEM/EDS data allows determination of the limit of solid solution of the pyrochlore phase with respect to tetravalent actinide (U) as 12–14 wt. %. Principle phases in the second series were garnet:
(Y2.82–2.88Gd0.13–0.14)(Al4.69–4.74Ga0.17–0.22Mo0.05–0.16)O12 and Mo-Al-Ga alloy. Small amounts of perovskite - (Y0.86Gd0.12)(Al0.93Ga0.05Mo0.03)O3, Mo, and Al oxides were also observed. Gd and Ga mainly entered in the garnet; small amounts of the elements were incorporated into perovskite (Gd), a metallic alloy, and perovskite (Ga).