[Show abstract][Hide abstract]ABSTRACT: Temperature-dependent strength of Bi-Sb-Te under uniaxial compression is investigated. Bi-Sb-Te samples were produced by three methods: vertical zone-melting, hot extrusion, and spark plasma sintering (SPS). For zone-melted and extruded samples, the brittle-ductile transition occurs over a temperature range of 200-350 °C. In nanostructured samples produced via SPS, the transition is observed in a narrower temperature range of 170-200 °C. At room temperature, the strength of the nanostructured samples is higher than that of zone-melted and extruded samples, but above 300 °C, all samples decrease to roughly the same strength.
[Show abstract][Hide abstract]ABSTRACT: Single crystals of solid electrolytes of the (ZrO2)1–x–y(Sc2O3)x(Y2O3)y (x = 0.035–0.11, y = 0‒0.02) system were grown by selective melt crystallization. Stabilization of ZrO2 only with Sc2O3 in the concentration range 9–11 mol % Sc2O3 did not afford crystals with a cubic structure, and only the introduction of additional Y2O3 stabilizers afforded uniform transparent single-phase cubic crystals. All the crystals under study had high microhardness, but low crack resistance. The ion conductivity of crystals with 6 and 9 mol % Sc2O3 (6ScZr and 9ScZr, respectively) is comparable to that of 8 mol % Y2O3-stabilized ZrO2 (8YSZ), which is the most suitable electrolyte in the ZrO2–Y2O3 binary system. The specific conductivity of crystals containing 8–10 mol % Sc2O3 and 1–2 mol % Y2O3 exceeds that of other materials including 8YSZ. The maximum conductivity in the given range of compositions is inherent in the cubic phase with 10 mol % Sc2O3 and 1 mol % Y2O3 (10Sc1YZr).
Article · Jul 2016 · Russian Journal of Electrochemistry
[Show abstract][Hide abstract]ABSTRACT: For the first time crystals of the (ZrO2)1-x-y(Sc2O3)x(Y2O3)y solid solutions (x = 0.08 – 0.11; y = 0.01 – 0.02) have been grown by directional melt crystallization. We have determined the range of melt compositions for which growth from the melt produces of the (ZrO2)1-x-y(Sc2O3)x(Y2O3)y solid solution single crystals. The single-phase optically transparent single crystals following composition were grown: (ZrO2)0.9(Sc2O3)0.08(Y2O3)0.02; (ZrO2)0.89(Sc2O3)0.09(Y2O3)0.02; (ZrO2)0.89(Sc2O3)0.10(Y2O3)0.01; (ZrO2)0.88(Sc2O3)0.10(Y2O3)0.02. Comprehensive study of the crystal structure by using XRD, transmission electron microscopy, and Raman spectroscopy revealed that the all single crystals, which is identified by XRD data as cubic one, in fact have t” tetragonal structure, which forms by small displacement of oxygen ions along the c-axis. Data on the phase stability of the crystals during mechanical crushing were obtained. The electrical conductivity was measured as a function of temperature by electrochemical impedance spectroscopy. It is established that (ZrO2)0.89(Sc2O3)0.10(Y2O3)0.01 crystals have the highest conductivity (0.168 S/cm at 1173 K).
[Show abstract][Hide abstract]ABSTRACT: We have studied the temperature dependence of the mechanical strength at uniaxial compression for solid solutions based on bismuth and antimony chalcogenides, which were prepared by three methods: (i) vertical zone melting (VZM), (ii) hot extrusion, and (iii) spark plasma sintering (SPS). In the samples of solid solutions obtained by VZM and extrusion, a brittle–ductile transition was observed in a wised temperature interval of 200–350°C. In nanostructured SPS samples, transition from brittle to plastic fracture was observed within 170–200°C. The room-temperature strength of nanostructured samples was eight to nine times as large as that of VZM samples, and the stress–strain curves of these materials were significantly different. At a temperature of about 300°C, the strength of nanostructured solid solutions decreases to nearly zero.
Full-text Article · Jan 2016 · Technical Physics Letters
[Show abstract][Hide abstract]ABSTRACT: This paper reports an x-ray diffraction, scanning and transmission electron microscopy study of regularities in the formation of defect structures in thermoelectric materials at different stages of plastic flow during equal-channel angular pressing in a three-channel configuration. We show that this deformation setup produces a homogeneous fine-grain structure with a preferential texture in which grain cleavage planes arrange along the extrusion axis. These studies of the structure and properties of thermoelectric materials were used to choose the optimum temperature for equal-channel angular pressing corresponding to lower pre-recrystallization temperatures.
Article · Oct 2015 · Journal of Electronic Materials
[Show abstract][Hide abstract]ABSTRACT: The structure of partially stabilised zirconia (PSZ) crystals has been studied as a function of the Y2O3 stabilising oxide concentration using X-ray diffraction and transmission electron microscopy. Hardness and fracture toughness were measured using microhardness indentation. We demonstrate that directed melt crystallisation grown PSZ crystals contain two tetragonal phases (t and t′) that differ in the degree of tetragonality, and an increase in the Y2O3 concentration in the crystals increases the content of the non-transformable t′ phase. Experiments have demonstrated that an increase in the concentration of the stabilising oxide increases the concentration of positively charged oxygen vacancies, the F++ centres, which increase the lattice parameter and stabilise the structure of the crystals. An increase in the Y2O3 concentration changes the type and size of twin domains. The strength (fracture toughness) of the crystals was demonstrated to be proportional to the content of the transformable t phase.
Full-text Article · Jun 2015 · Journal of the European Ceramic Society
[Show abstract][Hide abstract]ABSTRACT: The temperature dependences of the electrical conductivity and Hall coefficient of spark-plasma-sintered nanostructured thermoelectric materials based on p-Bi0.4Sb1.6Te3 solid solution were measured in the range of 15 K to 300 K for a set of samples sintered at different temperatures from 300°C to 550°C. These data allow estimation of the mean free path of holes. Analysis of the transport coefficients together with information on the size and internal structure of the nanocrystalline grains indicates the important role of point defects in hole scattering, being more intensive for samples obtained at lower sintering temperature. The possible nature of the defects is discussed based on the transport and structural data.
Full-text Article · Jun 2015 · Journal of Electronic Materials
[Show abstract][Hide abstract]ABSTRACT: The structure of PSZ crystals has been studied as a function of the content of the stabilizing impurity (Y2O3) by X–ray diffraction, transmission electron microscopy (TEM) and atomic-force microscope (AFM). The hardness and fracture toughness have been measured by microindentation. The study has shown that PSZ crystals obtained by directional solidification of the melt consist of two tetragonal phases (t and t’) with varying degrees of tetragonality. Increasing the stabilizing impurity concentration leads to an increase in the volume fraction of the “untransformable” t’ phase. Experiments have shown that an increase in the concentration of the stabilizing impurity leads to a growth in the amount of positively charged oxygen vacancies (the F++–centers) which increase the lattice parameter and stabilize the structure. The character of the twinned structure changes depending on the concentration of the stabilizing impurity. In PSZ crystals with Y2O3 concentration from 2.8 to 3.2 mol. % twins first, second and third orders as well as large twins consist of smaller twin domains are observed. At high concentrations of stabilizing impurities (3.7–4.0mol. %) the twin structure becomes smaller and more uniform. This suggests that twinning occurs simultaneously and is localized within small volumes. The character of the twinned structure changes depending on the concentration of the stabilizing impurity. This work shows that the quantity of hardening (fracture toughness) is proportional to the content of the transformable t phase.
[Show abstract][Hide abstract]ABSTRACT: The structure of PSZ crystals have been studied in relation to the content of the stabilizing impurity
(Y2O3) by X-ray diffraction and transmission electron microscopy. The measurement of both hardness
and fracture toughness by microindentation have been carried out. Studies have shown that crystals of
PSZ obtained by directional solidification of the melt consist of two tetragonal phases (t and t’), with varying
degrees of tetragonality. The yttrium-enriched phase t’ is ‘‘untransformable’’ in contrast to the t phase,
with a lower content of yttrium, which, under the influence of mechanical stress, undergoes a martensitic
transition to the monoclinic form. Increasing the stabilizing impurity concentration leads to an increase
in the volume fraction of the ‘‘untransformable’’ phase. Increasing the concentration of Y2O3 also affects
the form and dispersion of the twin domains. The character of the twinned structure changes depending
on the concentration of the stabilizing impurity and the hierarchy of the twinning disappears above
3 mol.% Y2O3. In this work it is shown that the quantity of hardening (fracture toughness) is proportional
to the content of the transformable t phase.
Full-text Article · Jan 2014 · Journal of Alloys and Compounds
[Show abstract][Hide abstract]ABSTRACT: The influence of the implantation of silicon single crystals by fluorine, nitrogen, oxygen, and neon ions on the distribution of strain and the static Debye-Waller factor in the crystal lattice over the implanted-layer depth has been investigated by high-resolution X-ray diffraction. The density depth distribution in the surface layer of native oxide has been measured by X-ray reflectometry. Room-temperature implantation conditions have ensured the equality of the suggested ranges of ions of different masses and the energies transferred by them to the target. It is convincingly shown that the change in the structural parameters of the radiation-damaged silicon layer and the native oxide layer depend on the chemical activity of the implanted ions.
Full-text Article · Dec 2013 · Crystallography Reports
[Show abstract][Hide abstract]ABSTRACT: The dependence of the thermoelectric properties of the nanostructured bulk (Bi,Sb)2Te3 material on the composition and the spark plasma-sintering (SPS) temperature T
SPS has been studied. It has been revealed that the Bi0.4Sb1.6Te3 solid solution sintered at a temperature of 450–500°C has a thermoelectric figure of merit ZT = 1.25–1.28. The dependence of thermoelectric properties on the sintering temperature T
SPS above 400°C is correlated to the transformation of the fine structure of the material due to the rearrangement of point vacancy-donor defects in the process of repeated recrystallization. It has been established that point structural defects make a considerable contribution to the formation of the thermoelectric properties of nanostructured material.
Full-text Article · Dec 2013 · Russian Microelectronics
[Show abstract][Hide abstract]ABSTRACT: The structure of partially stabilized zirconia crystals is investigated by X-ray diffractometry and transmission electron microscopy. It is shown that the combination of structural methods allowed one to reveal features of the structure and phase composition of these materials. Partially stabilized zirconia has a complex twin-domain structure. X-ray diffractometry with the use of K
β radiation shows the presence of two phases of the tetragonal modification of zirconia with different tetragonality in all investigated samples independently of the content of the stabilizing impurity. The combination of the locality of transmission microscopy with the integral nature of X-ray diffractometry allowed one to reveal the dependence of the dispersion of twin domains on the concentration of the stabilizing impurity. The use of transmission microscopy with high resolution demonstrates the hierarchy of twinning and the presence of twin domains ∼10 nm in width.
Full-text Article · Dec 2013 · Inorganic Materials
[Show abstract][Hide abstract]ABSTRACT: 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.
Full-text Article · Dec 2013 · Russian Microelectronics
[Show abstract][Hide abstract]ABSTRACT: Using X-ray diffraction and scanning electron microscopy, we have studied general aspects of defect structure formation in thermoelectric materials in different stages of plastic flow in the equal-channel angular pressing process with three channels. The results demonstrate that materials prepared using this deformation configuration have a fine-grained, homogeneous microstructure with a favorable texture, such that the cleavage planes of the grains are oriented along the extrusion axis. Studies of the structure and properties of the thermoelectric materials allowed us to optimize the equal-channel angular pressing temperature, which should be below the recrystallization onset temperature.
[Show abstract][Hide abstract]ABSTRACT: The phase composition and morphology of the twin structure of the
Y2O3-stabilized zirconia crystals (from 2.8 to 4.0
mol %) after the thermal treatment at 1600°C have been investigated
by X-ray diffractometry and transmission electron microscopy. It is
shown that as the concentration of the stabilizing
Y2O3 impurity increases, the character of the twin
structure changes, and the amount of the untransformed phase t'
increases. The dependence of the hardness and crack resistance of the
crystals of partially stabilized zirconia on the
Y2O3 concentration and the indenter orientation is
investigated using the microindentation method. The sample with the
lowest concentration of the stabilizing Y2O3
impurity turned out the most crack resistant. This can be explained by a
high content of tetragonal phase t in it, which provides the
transformation strengthening mechanism of the material, and by a more
multilevel character of twinning.
[Show abstract][Hide abstract]ABSTRACT: Ball milling with subsequent spark plasma sintering (SPS) was used to fabricate bulk nanothermoelectrics based on Bix
Te3. The SPS technique enables reduced size of grains in comparison with the hot-pressing method. The electrical and thermal conductivities, Seebeck coefficient, and thermoelectric figure of merit as functions of temperature and alloy composition were measured for different sintering temperatures. The greatest value of the figure of merit ZT = 1.25 was reached at the temperature of 90°C to 100°C in Bi0.4Sb1.6Te3 for sintering temperature of 450°C to 500°C. The volume and quantitative distributions of size of coherent dispersion areas (CDA) were calculated for different sintering temperatures. The phonon thermal conductivity of nanostructured Bix
Te3 was investigated theoretically taking into account phonon scattering on grain boundaries and nanoprecipitates.
Full-text Article · Jul 2013 · Journal of Electronic Materials