Co-crystallization of zinc oxide (ZnO) and zinc telluride (ZnTe) from a melt at high pressure results in the formation of ZnO-ZnTe composites with interesting physical properties that differ from those of the initial phases. The features of co-crystallization in the ZnO-ZnTe system at high pressure were studied using powder X-ray diffraction, scanning (SEM) and transmission (TEM) electron microscopy, energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and electron paramagnetic resonance (EPR) of the quenched samples, and a mechanism of successive (layer-by-layer) crystallization from the melt was proposed. Measurements of the Hall effect and thermoelectric properties revealed that the composites exhibit p-type conductivity. The Seebeck coefficients and temperature dependences of electrical and thermal conductivity were also determined.

Charge carrier and phonon dynamics tuning are promising approaches for transport property modulation. Improvement of thermoelectric (TE) parameters via atomic substitution and band engineering is prevalent. Besides, carrier effective mass (m*) is a crucial factor that has a noteworthy influence on TE properties. Transition metals (TMs), possessing outstanding valence electronic properties and distinctive electronic state distributions, have recently been used as potential candidates for enhancing TE performance. Here, we report the structural, electronic, and TE characteristics of p-type Sb2Te3 by TM (=Fe, Co, Ni) doping. Consequently, the synergistic amelioration of electrical and thermal transport properties is elucidated. Structural and phonon vibrational properties are characterized by synchrotron powder x-ray diffraction and Raman spectroscopic (RS) measurements. Raman peak position and full-width at half-maximum provide insight into electron–phonon interactions and phonon anharmonicity. Anharmonic phonon–phonon interaction is illustrated via a four-phonon decay model. Furthermore, optothermal RS measurement is used to estimate the thermal conductivity κ of the samples. A reduction in the lattice thermal conductivity, κL, is observed after TM doping. Experimentally measured transport parameters, viz., S(T), ρ(T), and nH(T) are simulated via the Boltzmann transport equation (BTE), and reasonable quantitative agreement between the experimental and simulated data is obtained. The role of m* and valence band convergence, as estimated from BTE analysis, is highlighted. Weighted mobility and m* are found to be increased, significantly enhancing the power factor in the Co-doped sample. As compared to its pristine counterpart, around three times the improvement of the ZT value in Sb1.97Co0.03Te3 is reported.

Carbon nanoparticles (CNPs) are attracting great attention as potential multifunctional agents for biomedical applications because of their bright fluorescence, low toxicity and flexibility of their physico-chemical properties. In the present paper, aqueous solutions of CNPs doped with gadolinium (Gd) (Gd-CNPs) within a widely varying range of Gd concentrations were prepared by hydrothermal synthesis. The influence of Gd doping on the optical properties and magnetic resonance (MR) relaxivity of Gd-CNPs was revealed. The Gd content was determined using X-ray fluorescence and spectrophotometry analysis. The composition of surface functional groups and coordination of Gd ions in Gd-CNPs were established by means of IR absorption spectroscopy and X-ray photoemission spectroscopy (XPS). The optical properties of Gd-CNPs in aqueous solutions were characterized by means of UV-visible-near-IR absorption spectroscopy and photoluminescence measurements with different excitation wavelengths. The local surroundings of Gd ions and paramagnetic centers in Gd-CNPs were probed by using electron paramagnetic resonance (EPR) spectroscopy. MR proton relaxation measurements in aqueous solutions of Gd-CNPs were carried out to determine the effect of Gd concentration on their MR contrasting. The obtained results characterize the coordination of Gd ions in Gd-CNPs and demonstrate new insights for controlling the optical and MR contrast properties of these nanoparticles for biomedical applications.

Magnesium doped polycrystalline ceramic samples of cooper chromite (I) with 0.6-4.0 at % Mg content have been synthesized. Phase composition of ceramics has been investigated by X-ray diffraction. Temperature dependencies of electrical resistivity and Seebeck coefficient have been measured by four probe method and analyzed in frame of variable range hopping conductivity. The density of localized electronic states and characteristic energy of its variation near Fermi energy have been estimated. It was obtained that the density of localized states at Fermi energy increases with an increase of Mg content, while characteristic energy of variation of localized state density near Fermi energy decreases. Obtained results show that relatively large values of Seebeck coefficient in Mg doped copper chromite (I) can be understood within variable range hopping transport of holes with rapidly increasing density toward valence band maximum.

The paper shows the necessity and relevance of performing precise specific heat measurements for the existing and newly synthesized substances and solids at low temperatures. The authors present GET 79-2020 State Primary Special Standard of the unit of specific heat of solids in the temperature range from 2 to 300 K, describing its design, operating principle, and the results of metrological examination. GET 79-2020 comprises the developed reference throttling cryostat and a cell for measuring specific heat that ensure efficient and prompt cooling of the test sample, as well as a reduction in uncontrolled heat fluxes, during measurement. GET 79-2020 can realize the unit of specific heat of solids within the range of 0.03–718 J/(kg·K) and the temperature range of 2–300 K. A method for measuring specific heat using the developed cell is described. The authors examine the metrological characteristics of GET 79-2020, estimating the uncertainty budget for realizing the unit of specific heat of solids. The obtained results extend the temperature range of measurements, expanding the fleet of working standards (measures) for heat capacity measuring instruments, verified using GET 79-2020.

The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgxZn1-xO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction. Transmission electron microscopy was used to study the particle size of nanocrystalline precursors, while the presence of Li, Na, and K metals in rock salt ZnO was detected by electron energy-loss spectroscopy and X-ray photoelectron spectroscopy in MgxZn1-xO alloys. Electron paramagnetic resonance measurements revealed the acceptor behavior of Li, Na, and K dopants based on the influence of the latter on native defects and natural impurities in ZnO-MgO alloys. In addition, diffuse reflectance spectroscopy was used to derive band gaps of quenched rock salt ZnO and its alloys with MgO.

Titanium dioxide (TiO2) nanocrystals are one of the most promising materials for modern photocatalysis applications, having unique properties such as a huge specific surface area and affordability of synthesis. However, the facile fabrication of TiO2-based photocatalysts active in regular daylight remains a major challenge. In this work, aiming to create such a nanocrystalline material by a very simple technology, we provide a detailed analysis of the paramagnetic centers (PCs) and their photoinduced reactions in N- and Nb-codoped TiO2 nanocrystals. The resulting powders show a surface area up to 170 m(2)/g and an intense visible-light photocatalysis of rhodamine 6G with reaction rate k = 0.087 min(-1). Ti3+, N-center dot, and O-2(-) PCs are observed and studied using electron paramagnetic resonance spectroscopy. We also present a new approach to the study of photoinduced processes in nanocrystalline photocatalysts-a simple theoretical model of kinetics of these PCs, which well predicts their behavior and variations of their concentration under illumination. Our results indicate that the obtained Nb-N-TiO2 nanocrystals with a high concentration of PCs on the sample surface can be used in cutting-edge industries, paving the way for the most advanced photocatalytic systems operating in sunlight.

Magnesium-doped polycrystalline ceramic samples of cooper chromite (I) have been prepared by solid phase synthesis. Phase composition and crystal structure of synthesis have been investigated by X-ray diffraction. Microstructure of samples has been investigated by scanning electron microscopy. Thermal conductivity and electrical conductivity have been measured in the temperature range 78<T<320 K. Significant reduction of thermal conductivity with an increase of synthesis duration have been observed. This effect was explained by formation of small amount of MgCr2O4 and Cr2O3 and CuO crystallites operating as effective phonon scatters. Formation of the MgCr2O4 phase is observed in X-ray diffraction patterns and SEM images of the samples with Mg content higher than 3 at. %. Formation of a small amount of Cr2O3 or CuO phase could be due to deviation of precursor's content from stoichiometry. Obtained results open a perspective of thermoelectric figure of merit enhancement for copper chromite-based material.

Electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements are used to study samples of ceramic solid solutions CuCr1 – xMgxO2 (x = 0–0.013). An analysis of the temperature dependences of the EPR linewidth, static magnetic susceptibility, and the effect of illumination on the EPR spectra indicates two mechanisms for the effect of magnesium doping on the magnetic properties of copper chromite. The substitution of chromium by magnesium in the crystal lattice suppresses antiferromagnetic fluctuations and leads to a decrease in the EPR linewidth and an increase in magnetic susceptibility at a temperature close to the temperature of the antiferromagnetic transition. An increase in the concentration of mobile holes leads to a decrease in the spin relaxation time of chromium ions. The data obtained are of interest both for fundamental physics and for practical applications in the field of solar energy.

The thermoelectric properties of Sb2 – xCuxTe3 single crystals (0 ≤ x ≤ 0.10) synthesized by the Bridgman method are studied in the temperature range of 77 K < T < 350 K. It turns out that the hole concentration and electrical conductivity strongly increase, while the Seebeck coefficient slightly decreases when Sb2Te3 crystals are doped with copper. The thermal conductivity of crystals doped with copper is somewhat higher than that of the initial Sb2Te3 crystals. As a result, the thermoelectric figure of merit ZT increases with increasing copper content at T > 300 K. In addition, the quantum mobility of holes μq in Sb2 – xCuxTe3 (0 ≤ x ≤ 0.10), Sb2 – xSnxTe3 (0 ≤ x ≤ 0.01), and Sb2 – xTlxTe3 (0 ≤ x ≤ 0.05) single crystals is measured using data on the Shubnikov–de Haas (SdH) effect. Electron paramagnetic resonance (EPR) measurements show that copper ions in the studied samples are most likely in the spinless Cu+1 state.

In 2011, a working group of the Consultative Committee for Thermometry published their best estimates of the differences between the thermodynamic temperature T and its approximation (T90), the temperature according to the International Temperature Scale of 1990, ITS-90. These consensus estimates, in combination with measurements made in accordance with ITS-90, are an important alternative to primary thermometry for those requiring accurate measurements of thermodynamic temperature. Since 2011, there has been a change in the definition of the kelvin and significant improvements in primary thermometry. This paper updates the (T − T90) estimates by combining and analyzing the data used for the 2011 estimates and data from more recent primary thermometry. The results of the analysis are presented as a 12th-order polynomial representing the updated consensus values for the differences and a sixth-order polynomial for their uncertainty estimates.

We report the enhancement of electron mobility and power factor for 3D topological insulator Bi2Te3 with Cobalt (Co) doping. Thermal variation of resistivity (rho), thermopower (S), carrier concentration (n(H)), magneto-resistance (MR), and magnetization measurements have been performed on synthesized Cobalt-doped n-type Bi2Te3, viz., Bi2-xCoxTe3 (x = 0, 0.05, and 0.1) samples. Theoretical simulation of electrical and thermal transport parameters has been done in the frame of the Boltzmann equation approach and shows satisfactory agreement with experimental results. The thermoelectric performance, as estimated through power factor is found to increase with Co doping, with an enhancement of similar to 47% is observed for Bi1.9Co0.1Te3 sample. The positive linear MR and nearly cusp like behaviour at low field and low temperature confirms the presence of weak anti-localization (WAL) effects in pristine and Co-doped Bi2Te3 samples. The field-dependent magnetization showing a cusp-like nature in the susceptibility data around zero field regions signifies the existence of topological surface state (TSS). MR along with magnetization data confirms the robustness of TSS with Co doping.

ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO.

We report the enhancement of electron mobility and power factor for 3D topological insulator Bi 2 Te 3 with Cobalt (Co) doping. Thermal variation of resistivity ( ρ ), thermopower ( S ), carrier concentration ( n H ), magneto-resistance (MR), and magnetization measurements have been performed on synthesized Cobalt-doped n -type Bi 2 Te 3 , viz., Bi 2− x Co x Te 3 ( x  = 0, 0.05, and 0.1) samples. Theoretical simulation of electrical and thermal transport parameters has been done in the frame of the Boltzmann equation approach and shows satisfactory agreement with experimental results. The thermoelectric performance, as estimated through power factor is found to increase with Co doping, with an enhancement of ~47% is observed for Bi 1.9 Co 0.1 Te 3 sample. The positive linear MR and nearly cusp like behaviour at low field and low temperature confirms the presence of weak anti-localization (WAL) effects in pristine and Co-doped Bi 2 Te 3 samples. The field-dependent magnetization showing a cusp-like nature in the susceptibility data around zero field regions signifies the existence of topological surface state (TSS). MR along with magnetization data confirms the robustness of TSS with Co doping.

This article presents the relevance of precise thermal conductivity measurements of solid materials used in heat exchange and heat insulating devices at low temperatures. The dependence of thermal conductivity of solids on the chemical composition and methods of mechanical and thermal processing of the material are considered at low temperatures. The device, principle of operation, and results of metrological studies of the State primary special standard of the unit of thermal conductivity of solids in the temperature range from 2 K to 300 K GET 141-2020 are presented. Compared to GET 141-84, in effect until 2020, GET 141-2020 includes the fabricated cryostat and a cell for measuring thermal conductivity. The range of reproduction of the unit of thermal conductivity of solids in GET 141-2020 is expanded compared to that of GET 141-84 from 0.1–10 W/(m·K) to 0.05–15 W/(m·K), and the range of temperature change is increased from 4.2–90 K to 2–300 K. A method of thermal conductivity measurements using the developed cryostat is described. Methods for ensuring a reliable thermal contact between the test sample and the heat-measuring plates of the heater and of the cell body are elaborated. The metrological characteristics of GET 141-2020 are analyzed; the measurement uncertainty budget is calculated when reproducing the unit of thermal conductivity of solids. GET 141-2020 is used to calibrate thermal conductivity measurements during the verification and calibration of equipment for measuring thermal conductivity.

Nanosized titanium dioxide (TiO2) is currently being actively studied by the global scientific community, since it has a number of properties that are important from a practical point of view. One of these properties is a large specific surface, which makes this material promising for use in photocatalysts, sensors, solar cells, etc. In this work, we prepared photocatalysts based on TiO2 nanotubes for converting carbon dioxide (CO2) into energy-intensive hydrocarbon compounds. Efficient gas-phase CO2 conversion in the prepared single-walled TiO2 nanotube-CuxO composites was investigated. Parameters of defects (radicals) in composites were studied. Methanol and methane were detected during the CO2 photoreduction process. In single-walled TiO2 nanotubes, only Ti3+/oxygen vacancy defects were detected. The Cu2+ centers and O2− radicals were found in TiO2 nanotube-CuxO composites using the EPR technique. It has been established that copper oxide nanoparticles are present in the TiO2 nanotube-CuxO composites in the form of the CuO phase. A phase transformation of CuO to Cu2O takes place during illumination, as has been shown by EPR spectroscopy. It is shown that defects accumulate photoinduced charge carriers. The mechanism of methane and methanol formation is discussed. The results obtained are completely original and show high promise for the use of TiO2-CuxO nanotube composites as photocatalysts for CO2 conversion into hydrocarbon fuel precursors.

Сообщаются результаты исследования термоэлектрических свойств в интервале температур 77300 K. Кроме этого приводятся результаты измерений квантовой подвижности дырок μ q из данных по эффекту Шубникова-де Гааза как в монокристаллах Sb 2-x Cu x Te 3 (0≤ x≤ 0.10), так и в монокристаллах Sb 2-x Sn x Te 3 (0≤ x≤0.01); Sb 2-x Tl x Te 3 (0≤ x≤0.05). Измерения ЭПР показывают, что атомы меди в исследованных образцах, скорее всего, находятся в бесспиновом состоянии Cu +1 . Ключевые слова: термоэлектрическая эффективность, теллурид сурьмы, электронный парамагнитный резонанс, эффект Шубникова-де Гааза.

Improvement in thermoelectric parameters is reported with graphite incorporation in n-type Bi2Te3/graphite nanocomposite systems. In-depth thermoelectric properties of nanostructured Bi2Te3/graphite composites are probed both microscopically and macroscopically using x-ray diffraction, Raman spectroscopy, inelastic neutron scattering, and measurement of the temperature dependence of thermal conductivity κ, Seebeck coefficient S, resistivity ρ, and carrier concentration nH. Raman spectroscopic analysis confirms that graphite introduces defects and disorder in the system. Graphite addition induces a large (∼17%) decrease of κ, originating from a strong phonon scattering effect. A low lattice thermal conductivity, κL, value of 0.77 W m−1 K−1, approaching the κmin value, estimated using the Cahill–Pohl model, is reported for Bi2Te3 + 1.0 wt. % graphite sample. Graphite dispersion alters the low-energy inelastic neutron scattering spectrum providing evidence for modification of the Bi2Te3 phonon density of states. Improvement in other thermoelectric parameters, viz., Seebeck coefficient and resistivity, is also reported. Theoretical modeling of electrical and thermal transport parameters is carried out and a plausible explanation of the underlying transport mechanism is provided assuming a simple model of ballistic electron transport in 1D contact channels with two different energies.

We investigated thermoelectric and magnetic properties of polycrystalline CuCr1-xMgxO2 (x = 0; 0.002; 0.008; 0.015; 0.030) ceramic samples, synthesized by a special chemical homogenization method (nitrate synthesis). Temperature dependencies of magnetization were measured in magnetic field H = 1000 G. Transition temperature do not noticeably shift with variation of Mg content. Seebeck coefficient S increases with temperature for all investigated samples. At room temperature S decreases from nearly 700 mV/K in pristine material to about 250 mV/K for the copper chromite with 3at.% Mg. Heat conductivity k of all investigated samples is close to the heat conductivity of undoped CuCrO2 crystals. Resistivity of investigated samples decreases several orders of magnitude with increase of Mg content up to 3%. Temperature dependence of resistivity and Seebeck coefficient was interpreted by hopping conductivity in the presence of the Coulomb (parabolic) gap in the density of states. ? 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 17th European Thermoelectric Conference.

Thermoelectric performance largely depends on the reduction of lattice thermal conductivity (κL). The study of the thermal conductivity (κ) of a Sb2Te3/graphite nanocomposite system demonstrates ∼40% reduction in κL with graphite incorporation. A plausible explanation of intrinsic low κL observed in Sb2Te3 based system is presented by modeling experimental specific heat (Cp) data. Raman spectroscopy measurement combined to X-Ray diffraction data confirms the presence of graphite as separate phase in the composite sample. It is found that phonon scattering dominates heat transport mechanism in the nanostructured Sb2Te3/graphite composite. Large reduction in κL is accomplished by intensifying scattering rate of phonons via various sources. Graphite introduces effective scattering sources, i.e., defects of different dimensionalities in synthesized nanocomposite sample. Furthermore, graphite mediates phonon-phonon coupling and enhances lattice anharmonicity, which causes an intrinsic scattering of phonons with all frequencies in the Sb2Te3/graphite nanocomposite sample. Dislocation density and phonon anharmonicity of the synthesized samples are estimated from in depth analysis of temperature dependent synchrotron powder diffraction and Raman spectroscopic data. κL value as low as 0.8 W m−1K−1 at 300 K, achieved with graphite dispersion in Sb2Te3 based composite system makes the present comprehensive study an interesting concept to be developed in thermoelectric materials.