Effect of Sr Doping on Structural and Transport Properties of Bi2Te3

Search for doped superconducting topological insulators is of prime importance for new quantum technologies. We report on fabrication of Sr-doped Bi2Te3 single crystals. We found that Bridgman grown samples have p-type conductivity in the low 1019 cm−3, high mobility of 4000 cm2V−1s−1, crystal structure independent on nominal dopant content, and no signs of superconductivity. We also studied molecular beam epitaxy grown SrxBi2−xTe3 films on lattice matched (1 1 1) BaF2 polar surface. Contrary to the bulk crystals thin films have n-type conductivity. Carrier concentration, mobility and c-lattice constant demonstrate pronounced dependence on Sr concentration x. Variation of the parameters did not lead to superconductivity. We revealed, that transport and structural parameters are governed by Sr dopants incorporation in randomly inserted Bi bilayers into the parent matrix. Thus, our data shed light on the structural position of dopant in Bi2Te3 and should be helpful for further design of topological insulator-based superconductors

Development of ion thruster IT-500

A high-power ion thruster IT-500 was designed, manufactured and tested at Keldysh Research Center within a transport-power module project. This module is being designed to perform near-Earth space and interplanetary transport missions. In its nominal operation mode, IT-500 provides thrust in the range from 375 to 750 mN at specific impulse of 70 000 m/s and thrust efficiency of 0.75. Due to a high cost of the experimental testing of a large thruster, the emphasis was placed on the numerical optimization of the thruster design. The thruster completed performance tests and a 300 h wear test. The output characteristics of the thruster, obtained during the tests, confirmed the correctness of the provisional numerical optimization. IT-500 design, performance, and validation of the design approaches are discussed in this paper

Nucleophilic Substitution Reactions in the [B3H8]− Anion in the Presence of Lewis Acids

As a result of our study on the interaction between the octahydrotriborate anion with nucleophiles (Nu = THF, Ph3P, Ph2P-(CH2)2-PPh2 (dppe), Ph3As, Et3N, PhNH2, C5H5N, CH3CN, Ph2CHCN)) in the presence of a wide range of Lewis acids (Ti(IV), Hf(IV), Zr(IV), Al, Cu(I), Zn, Mn(II), Co(II) halides and iodine), a number of substituted derivatives of the octahydrotriborate anion [B3H7Nu] are obtained. It is found that the use of TiCl4, AlCl3, ZrCl4, HfCl4, CuCl and iodine leads to the highest product yields. In this case, it is most likely that the reaction proceeds through the formation of an intermediate [B3H7-HMXnx], which was detected by NMR spectroscopy. The structures of [Ph3P·B3H7] and [PhNH2·B3H7] were determined by X-ray diffraction