Structure of Bi<Subscript>2</Subscript>Se<Subscript>0.3</Subscript>Te<Subscript>2.7</Subscript> alloy plates obtained by crystallization in a flat cavity by the Bridgman method

The property anisotropy in Bi₂Se_0.3Te_2.7 alloy is analyzed by constructing index surfaces for the thermoelectric figure of merit and thermal expansion coefficient. Texture is an important factor forming the property anisotropy and technological applicability of an ingot for fabricating modules. The property anisotropy is analyzed based on studying the texture in ingots produced by the modified Bridgman method (thermoelectric plate growth in a flat cavity). Analysis of the texture shows that not only the crystallization rate, but also the crystallization cavity design is an important factor for the proposed crystallization method, affecting the formation of the thermoelectric-material structure. As the plate thickness is decreased by changing the heat removal conditions in a thin gap, a more perfect structure can be obtained.     

New trends in the development of the technology for the production of ultraviolet light-emitting diodes

Some results on the creation of ultraviolet light-emitting diodes based on GaN/AlGaN heterostructures grown on aluminum nitride (AlN) substrates using the method of chloride-hydride epitaxy are presented. The peak wavelengths lie within the range of 360–365 nm, the width of a spectral curve is 10–13 nm, and the output optical power of light-emitting diode chips is 50 mW at a current of 350 mA.     

Influence of the initiation energy on development of hydrogen–air mixtures combustion in large spherical volumes

We investigate the influence of the initiation energy on the development of burning in hydrogen–air mixtures with an hydrogen content of 7–31% (volume). We initiated the mixtures in the center of the spherical reaction volume, 7–40 m³ in size, by energies from 1 J up to 4600 J. The reaction volume was bordered by a thin rubber envelope and located inside the 910 m³ spherical explosion chamber. We registered the flame front movement by means of the ionization sensors, the video camera, and the high-speed video camera.     

Change in the mechanism of conductivity in ZrO<Subscript>2</Subscript>-based crystals depending on the content of stabilizing Y<Subscript>2</Subscript>O<Subscript>3</Subscript> additive

The interrelationship between the structure, phase composition, and transport characteristics of solid electrolytes based on ZrO₂ has been studied as dependent on the content of stabilizing Y₂O₃ additive. It is established that twin boundaries do not lead to the appearance of additional mechanism of ionic conductivity acceleration in ZrO₂–Y₂O₃ crystals. The maximum conductivity has been observed in ZrO₂–(8–10) mol % Y₂O₃ crystals containing a t” phase, in which oxygen atoms are displaced from high-symmetry positions characteristic of the cubic phase.     

Experimental and theoretical study of the thermoelectric properties of copper selenide

The temperature dependences of the specific heat, thermal conductivity, coefficient of thermal expansion (CTE), and transport coefficients (electrical conductivity and thermoelectric power) of copper selenide are experimentally and theoretically investigated in the temperature range of 300–873 K. The calculation results correlate with the experimental data up to a temperature of ~773 K. The maximum thermoelectric figure of merit of nanostructured copper selenide is ZT ~ 1.8. The correlation dependence between ZT and the thermal conductivity within the entire temperature range under consideration is shown.     

Influence of ionospheric perturbations on navigational determinations

An analysis is made of the influencing factors of a perturbed ionosphere on the navigational signal of a low-orbit space system. The results of theoretical and experimental investigations for the polar regions are given. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 5–9, April, 1999.     

Effect of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> stabilizer content and annealing on the structural transformations of ZrO<Subscript>2</Subscript>

The structure of partially stabilized zirconia crystals has been studied by transmission electron microscopy before and after annealing. Structural characterization of Y₂O₃-doped (2.8 to 4 mol %) zirconia before annealing showed that all of the samples consisted of twin domains whose size was dependent on the stabilizer content. Annealing at 2100°C increased the domain size in the composition range 2.8–3.7 mol % Y₂O₃ and reduced it at 4 mol % Y₂O₃. These structural changes allowed us to determine the position of the representative point relative to the phase boundary in the equilibrium phase diagram of the system.     

Optical properties and defects in GaAsN and InGaAsN films and quantum well structures

Photoluminescence and microcathodoluminescence spectra of thick-film GaAsN and InGaAsN structures and GaAs/InGaAsN, AlGaAs/InGaAsN quantum wells (QWs) were studied for InGaAsN layers with low nitrogen concentration of 0.35–0.5%. It is shown that in thick-film structures the bandedge luminescence intensity is strongly decreased in the row homoepitaxial GaAs, GaAsN on GaAs buffer, GaAsN, GaAs on GaAsN buffer, InGaAsN which correlates with the increasing concentration of electron traps with activation energy 0.53–0.55 eV. The type of defect bands in the thick-film structures was found to strongly depend on composition of the layers. For the GaAs/InGaAsN QW structures the intensity of luminescence was found to be more than an order of magnitude higher than in InGaAsN single films.