This work presents a study of the thermodynamic stabilities of the thorium boron carbides including a revised version of the Th-B binary system: (i) a maximum of 1 at.% Th dissolves in beta boron, (ii) the “hectoboride ThB66(O)” is found at ThB60, (iii) the B-rich boundary of the hexaboride Th1-x□xB6 (□ denotes a vacancy) extends according to its homogeneity region 0≤x≤0.22, (iv) novel thorium diboride with AlB2-type (a = 0.310(1) nm, c = 0.402(1) nm) forms in a peritectic reaction at ~2200°C. Based on DFT derived energies of formation, thermodynamic phase equilibria in the binary system Th-B have been calculated i.e. phase relations have been defined for Th-B up to the melting range.For all ternary Th-B-C compounds, density functional theory calculations were made within the pseudopotential approach of VASP utilizing a general gradient approximation for the exchange correlation functional. A metaGGA approach was then applied to all compounds in their equilibrium structures, which significantly lowered the enthalpies of formation for ThC and ThC2, whereas it had only a small impact on ThB4. Atomic volumes and charges were computed by the concept of Bader and distinctly ionic features are derived consisting of Th+2, B+1, B-½, C-1, C-2 and C-3 ions. All compounds are, however, of metallic character.

Thermodynamic modelling of the Nb-Sb system was performed by the CALPHAD method, based on SGTE data of the Gibbs energy for pure elements, as well as on data from experimental studies in the literature combined with our new information, obtained via DTA, EDX-EPMA, XPD and ab initio calculations. Our re-investigation confirms the three intermetallic compounds reported earlier: Nb3Sb, Ni5Sb4 and NbSb2. Particularly, our detailed study of the Nb-rich part of the system revealed an intermediate phase with a narrow composition range for Nb3Sb, extending at 950 °C from 74.0 at% Nb to 75.3 at% Nb (EMPA-WDX data). Battling a high Sb evaporation above about 1300 °C (monitored by thermogravimetry) high-temperature DTA data (Y2O3 crucibles) unambiguously defined the peritectic decomposition of Nb3Sb at 1840 ± 25 °C. In contrast to earlier information in the literature, Nb5Sb4 was found to form peritectically at 1550 ± 10 °C, whereas the temperature of the peritectic reaction of NbSb2 appeared at 1320 ± 10 °C. The eutectic temperature of 624 ± 8 °C was confirmed by low-temperature DTA measurement (sealed quartz ampoules). Furthermore, data on heat of formation for all the compounds were provided by ab initio calculations, which served to optimize model parameters for the calculation of the Nb-Sb phase diagram. The calculated binary phase diagram obtained agrees well with the experimentally determined one. The thermodynamic database is attached.

The paper reports on the phase stability of the (FeCoNi) 0.75 Cr 0.25-x Cu x HEA system with equimolar ratio of Fe, Co and Ni by differential scanning calorimetry (DSC) and measurements of physicochemical properties: density, electrical resistivity, Seebeck coefficient, thermal conductivity, and magnetic behaviour in a broad temperature region as well as hardness and elastic modulus at room temperature as a function of the gradual substitution of chromium by copper in a series of (FeCoNi) 0.75 Cr 0.25-x Cu x alloys with different mole fraction of Cu (x = 0, 0.05, 0.1, 0.15 and 0.2). DSC measurements showed that all alloys are thermally stable. Increasing content of Cu was found (i) to increase the formation of a fcc Cu-rich phase, (ii) to strengthen ferromagnetic interactions, resulting in rising ordered magnetic moments, as well as in growing ferromagnetic transition temperatures, and (iii) to distinctly change physical properties like electrical resistivity, thermal expansion, and mechanical properties. Experimental data regarding the phase stability are supported by CALPHAD calculations.

The Hf-Mn system is of a long-time interest due to the intermetallic Laves phase HfMn2, a hydrogen storage material. Although this system has been experimentally investigated by several authors and critical reviews and thermodynamic modelling have been performed, there is still a lack of reliable information, particularly as the phase "HfMn" (sometimes labelled as "Hf3Mn2" or "Hf2Mn") is suspected to be oxygen stabilized. This work includes a thorough investigation of the Hf-Mn phase equilibria employing diffusion zones, thermal analysis, powder and single crystal X-ray analyses, analytical electron microscopy as well as physical property studies of the Laves phase (magnetic susceptibility, specific heat, electrical resistivity and mechanical properties). The phase near "HfMn" was shown (TEM, WDX electron microprobe data, X-ray single crystal analysis) to be an oxygen stabilized phase with the formula Hf3+xMn3_xO1_y (defect eta-W3Fe3C type). Properties such as magnetic susceptibility/magnetization; 2-300 K, specific heat (2-1100 K), electrical resistivity (2-300 K) classify HfMn2 as a metallic spin-fluctuation system with itinerant paramagnetism, originating from 3d states at Mn-sites and local moment paramagnetism of antisite Mn-atoms at Hf-sites. Mechanical properties (elastic moduli from density functional theory (DFT) and nanoindentation as well as hardness) group the Laves phase among rather hard and brittle intermetallics. DFT modeling revealed that Hf3+xMn3_x is thermodynamically unstable, but significant gains in enthalpy of formation arise from the inclusion of oxygen atoms, stabilizing the eta phase. All phase diagram and DFT data together with the former literature information were used for the thermodynamic CALPHAD-type modelling of the Hf-Mn system.

The paper reports on the phase stability of the (FeCoNi)0.75Cr0.25-xCux HEA system with equimolar ratio of Fe, Co and Ni by differential scanning calorimetry (DSC) and measurements of physicochemical properties: density, electrical resistivity, Seebeck coefficient, thermal conductivity, and magnetic behaviour in a broad temperature region as well as hardness and elastic modulus at room temperature as a function of the gradual substitution of chromium by copper in a series of (FeCoNi)0.75Cr0.25-xCux alloys with different mole fraction of Cu (x = 0, 0.05, 0.1, 0.15 and 0.2). DSC measurements showed that all alloys are thermally stable. Increasing content of Cu was found (i) to increase the formation of a fcc Cu-rich phase, (ii) to strengthen ferromagnetic interactions, resulting in rising ordered magnetic moments, as well as in growing ferromagnetic transition temperatures, and (iii) to distinctly change physical properties like electrical resistivity, thermal expansion, and mechanical properties. Experimental data regarding the phase stability are supported by CALPHAD calculations.

Experimental and theoretical study of the Ag- Sn-Te system was carried out in the scope of the study. The isothermal sections at 350 and 500 °C were studied experimentally. The results were used together with other experimental data from the literature for the theoretical assessment of the system by the CALPHAD method. Generally, a very good agreement was obtained both for the phase diagram and for the enthalpies of mixing in the liquid phase. The existence of the ternary phase (AgxSn2-xTe2) was confirmed, and a slightly different composition (x = 0.8) was evaluated in the experimental part of the study.

Half-Heusler alloys, a non-centrosymmetric structure variant of the Heusler type, create a category of advanced thermoelectric materials. The thermal and phase stability of half-Heusler alloys TiFe1.33Sb and TixNb1-xFeSb (x = 0, 0.15), prepared by various techniques (hot pressing, ball milling or high-energy ball milling and hot pressing, as well as in one case with additional annealing), have been studied by means of differential thermal analysis and the Knudsen effusion method. The results from the measurement of phase transformations and evaporation of antimony, as the volatile element, supported by microstructure measurements and by diffusion profiles are presented and discussed in view of the long-term operation stability of the thermoelectric materials investigated. The alloys TiFe1.33Sb and TixNb1-xFeSb have all evidenced only a slight evaporation of antimony and have proven their long-term stability at temperatures well above the operation temperature of similar to 873 K.

Pb–Se–Te ternary system is of significant importance for thermoelectric applications. In spite of this, no systematic experimental or theoretical study of its phase diagram has been carried out up to now. The CALPHAD type theoretical assessment was done in the scope of this work for the Se–Te and Pb–Se–Te systems based on our own experimental work and the experimental results from literature. It was found out that the reassessment of the existing Se–Te phase diagram assessments is necessary because of some discrepancies between the experimental results and calculations for this system. This new dataset was consequently used for the new assessment of the Pb–Se–Te system and very good agreement was reached with existing experimental data.

With a high figure of merit, ZT, described in detail in the introduction, multi-filled CoSb3 skutterudites attract attention for their use as thermoelectric materials. In this work, the thermal and phase stability of n-type skutterudites, Sr0.07Ba0.07Yb0.07Co4Sb12, prepared by ball milling, hot pressing and high-pressure torsion or by combinations thereof, with ZT values of about 1.4, have been studied via differential thermal analysis and Knudsen effusion method. The results from evaporation of antimony, strontium, barium and ytterbium as the volatile elements and those from phase transformation measurements are presented. The information, supported by microstructure investigation and measurement of diffusion profiles, is summarized and the long-term operation stability of the studied bulk and nano-structured thermoelectrics is evaluated. Almost no strontium, barium and ytterbium evaporation and only a slight evaporation of antimony demonstrate a long-term operation stability of the bulk and nano-structured thermoelectrics investigated.

The constitution of the two phase diagrams Nb-Mn and Ta-Mn has been determined from light optical and transmission and scanning electron microscopy (LOM, TEM and SEM) with energy dispersive (EDX) as well as wavelength dispersive (WDX) X-ray spectroscopy, X-ray powder (XPD) and single crystal diffraction (XSCD), differential thermal analysis (DTA) and/or differential scanning calorimetry (DSC). The Laves phases NbMn2 and TaMn2 are the only binary compounds in these systems. High-temperature differential thermal analyses revealed congruent melting for NbMn2 with T,(NbMn2) = 1515 +/- 15 degrees C, whereas TaMn2 melts incongruently with T-m(TaMn2)= 1797 +/- 40 degrees C close to a depleted peritectic reaction. Both Laves phases engage in eutectic reactions l <-> (Mn) + Nb(Ta)Mn-2 (T-eut = 1220 +/- 10 degrees C at 4.9 at% Nb and T-eut = 1234 +/- 10 degrees C at 0.7 at% Ta, respectively). NbMn2 also forms a eutectic with (Nb): l <-> (Nb) + NbMn2 at T-eut = 1493 +/- 15 degrees C and 53.2 at% Nb. Mn shows remarkably large maximum solid solubilities of 19.4 at% Mn in (Nb) as well as of 21.3 at% Mn in (Ta). Detailed atom site distribution has been established for the Laves phases by means of temperature dependent X-ray single crystal data (both C14 - MgZn2-type). Combined data from XPD, EDX/WDX and SEM microstructure indicate that for both Laves phases extended homogeneity regions exist: Nb1+xMn2+x (62.5-73.0 at% Mn at 950 degrees C: -0.19 <= x <= 1.125) and Ta1+xMn2-x (59.5-68.5 at % Mn: -0.055 <= x <= 1.215). Density functional theory (DFT) calculations favor Nb(Ta)/Mn antisite occupation rather than defects. The phases, "NbMn" and "TaMn", adopted earlier in the literature as binary system inherent compounds, were shown (TEM, WDX electron microprobe data and X-ray Rietveld refinements) to be oxygen stabilized phases of the Ti4Ni2O type (so-called eta(eta)-phases) with modified Nb(Ta)/Mn site substitution to comply with the formula Nb(Ta)(3-x)Mn3+xO1-y (defect eta-W3Fe3C-type). From magnetic susceptibility and magnetization measurements, both oxide stabilized eta phases eta-Nb3Mn3O1-y and eta-Ta3Mn3O1-y were found to order ferromagnetically below T-c similar to 77 K, but the Laves phases NbMn2, TaMn2 reveal weakly temperature dependent paramagnetism. No trace of the rhombohedral kyphase (W6Fe7-type) has been encountered in our investigation of the two binary phase diagrams. Thermodynamic and transport properties (specific heat, electrical resistivity and magnetic susceptibility/magnetization) classify the Laves phases with metallic behavior whilst mechanical properties (elastic moduli from DFT and nanoindentation as well as hardness and thermal expansion) group both Laves phases among rather hard and brittle intermetallics. Based on (i) the experimentally derived constitution of the Nb-Mn and Ta-Mn systems, and (ii) on new own DFT data of the energy of formation of the Laves phases, a CALPHAD (CALculation of PHAse Diagrams) calculation of both systems was made providing a complete set of optimized thermodynamic data. Furthermore, the DFT calculations provided information on the instability of the eta-Ta3Mn3 structure and the atom-site specific stabilization effect of oxygen. (C) 2021 The Authors. Published by Elsevier B.V.

Half-Heuslerovy (H-H) slitiny jsou zname svými termoelektrickými vlastnostmi, ktere mohou být optimalizovany dotovanim tři jednotlivých podmřižek vhodnými prvky. Pokud se jedna o těkave prvky, jako je Sb nebo jine, je pro dlouhodobou tepelnou stabilitu těchto materialů důležite studium odpařovacich vlastnosti. Tento přispěvek se zabýva studiem tepelne a fazove stability H-H slitin (Ti,Nb)FeSb připravených lisovanim za tepla nebo kulickovým mletim a lisovanim za tepla, pomoci tepelne analýzy a Knudsenovy efuzni metody. Výsledky podpořene udaji z měřeni mikrostruktury a měřeni difuznich profilů jsou diskutovany s ohledem na fazove diagramy přislusných ternarnich systemů a na výsledky naseho předchoziho zkoumani dlouhodobe tepelne stability didymiem dopovaných skutteruditů typu p.

Soustava Co-Sb ma zvlastni pozornost kvůli existenci struktury skutteruditu CoSb3, ktera tvoři zaklad dopovaných termoelektrických materialů na bazi skutteruditu. K ziskani spolehlivých dat v castiv fazoveho diagramu Co-Sb Sb bohateho na Sb, ktera je důležita pro studium tepelne stability termoelektrických materialů na bazi skutteruditu a v niž existuje rozpor v publikovaných datech, byly připraveny experimentalni slitiny pokrývajici 80 až 100% Sb a zkoumany termickou a fazovou analýzou. Udaje byly porovnany s existujicimi literarnimi informacemi a bylo provedeno termodynamicke přemodelovani tohoto binarniho systemu, založene na přistupu CALPHAD.

Thermoelectric materials play an important role in the field of renewable energy for their ability of thermal energy conversion into electricity (thermoelectric generator) and reversibly electric energy conversion into thermal energy (thermoelectric heat pump or Peltier cooling). Doped CoSb3 based skutterudites represent one of the very promising categories for the development of highly efficient thermoelectric materials for the conversion of waste heat to electricity. The thermoelectric efficiency, however, is closely related to thermal and phase stability as the current materials contain volatile elements (Sb, Sr, Yb, etc.), which can evaporate at operation conditions and thus cause structure changes and damage the thermoelectric properties. For a better understanding of the thermal behaviour of complex multicomponent CoSb3 based skutterudite systems, a study of the thermal stability of primary CoSb3 skutterudite is necessary. In this work, the thermal and phase stability of primary CoSb3 skutterudite prepared by ball milling and hot pressing was investigated using thermal analysis and Knudsen effusion mass spectrometry performed on a Netzsch STA 409 CD/3/403/5/G apparatus, a specially-adapted type of the commercial STA 409 CD - QMS 403/5 Skimmer Coupling Instrument. Results, including data on phase transformations and those from vapour pressure measurements of antimony, supported by measurements of diffusion profiles and microstructure observations are summarized and used for evaluation of the long term thermal stability of the material.

Termoelektricke materialy jsou v oblasti zajmu diky sveschopnosti přeměnit odpadni teplo na elektrickou energii.Soucasný výzkum je orientovan na výzkum skuteruditů založenýchna mateřske struktuře CoSb3, jejimž dopovanim lze připravitmaterialy s vysokou termoelektrickou ucinnosti. Pro dopovani jevyuživano substituce kobaltu ve struktuře skuteruditu atomyželeza a soucasně přidavani intersticialnich přiměsi, ve forměkovů alkalických zemin a lanthanoidů. Zaměna kobaltu atomyželeza sice strukturu skuteruditu destabilizuje, přidavekneodymu, který vyplňuje ikosaedralni prazdna mista, působinaopak na strukturu skuteruditu stabilizacně. Výsledkem jeexistence stabilni struktury, ktera ma vysokou termoelektrickouucinnost. Termicka stabilita skuteruditu DD0.7Fe3CoSb12, kde DDje tzv. didymium (Nd + Pr), byla studovana prostřednictvimdiferencni termicke analýzy a výsledky byly konfrontovany sfazovými diagramy ternarnich podsoustav.

Promising materials for thermoelectric (TE) applications include skutterudites. The TE efficiency characterized by the ZT factor is only a partial route to the development of TE devices. The other part involves the thermal stability because the materials contain volatile elements such as Sb, Yb, etc. which can evaporate at operation conditions and negatively influence the TE properties. A serious attention is focused on study of doped bulk and nanostructured CoSb3 based skutterudites, especially those containing didymium. Coupling of thermal analysis and Knudsen effusion mass spectrometry is an effective tool for investigation of phase transformations and vaporization characteristics of the volatile components. This, supported by microstructure measurements as well as by investigation of master CoSb3 alloy, leads to evaluation of long term operation stability of the TE materials.

The temperature and phase stability of p-type skutterudites, DD0.7Fe3CoSb12, manufactured via various preparation techniques, all exhibiting a high ZT-level, have been studied by means of thermal analysis and Knudsen effusion mass spectrometry. The results from phase transformation measurements and characteristics of the evaporation of antimony, as the volatile element, supported by microstructure observations and by diffusion profiles are summarized and discussed in view of a full understanding of the degradation processes and knowledge of the long term operation stability of the bulk and nano-structured thermoelectrics studied. It was found out that the antimony evaporation is a complex diffusion kinetic process resulting in a stable Sb level dependent on the preparation route. The studied p-type skutterudites, DD0.7Fe3CoSb12, have proven their long term stability in thermoelectric devices at a maximum operation temperature of 600 °C. Complementary data on the structural, physical and mechanical properties of the materials are presented as well.

Thermodynamic modelling of chromium-based Laves phases containing Ti, Zr, Hf, Nb and Ta above room temperature was published in our papers. Using our values of Gibbs energies of elements extended to zero Kelvin temperature we have compared Gibbs energies of chromium-based Laves phases for their stable modifications at 0 K temperature with the Gibbs energies of respective elements at 0 K temperature. On the basis of this, we demonstrate the stability and metastability of equilibrium Laves phases with respect to elemental constituents at 0 K.

The synthesis of nanoalloys is one integral part of nanoscience and development of efficient preparative methods is a challenging task due to their chemical, phase, and morphological variability. Nanoparticles of metal alloys exhibit many interesting properties, such as depression of melting point, plasmon resonance, catalytic activity and magnetic properties. Nanoalloys can be prepared by many approaches, but the solvothermal synthesis, specifically in oleylamine is highly advantageous. Hot injection technique should ensure homogeneous conditions for nanoparticle nucleation and growth. AgNi and AgCu nanoparticles were synthetized by injection of metal precursors oleylamine solution to a mixture of oleylamine and octadecene at 230 °C. After 10 minutes, the reaction mixture was cooled down to room temperature in a water bath. Nanoparticles were isolated, purified, dispersed in hexane and characterized. Size, shape, morphology, elemental distribution, optical and magnetic properties were described by using various techniques. Core/shell structure of AgNi, importance of used precursors to final morphology of AgCu and simple technique for Janus or solid solution synthesis were demonstrated. The results of this research have been acquired within the CEITEC 2020 (LQ1601) project with financial contribution made by the MEYS CR within special support paid from the National Program for Sustainability II funds and by the Czech Science Foundation (GA 17-15405S). CIISB research infrastructure project LM2015043 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements at the CF X-ray Diffraction and Bio-SAXS and at the CF Cryo-electron Microscopy and Tomography CEITEC MU. STE M-EDS was carried out with the support of CEITEC Nano Research Infrastructure (ID LM2015041, MEYS CR, 2016–2019), CEITEC Brno University of Technology and was performed as part of a user project through Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, which is a U.S. Department of Energy (DOE) Office of Science user facility along with instrumentation provided by the DOE Office of Nuclear Energy, Fuel Cycle R&D Program, and the Nuclear Science User Facilities.

Thermodynamický popis soustavy Ag-Pb-Sn byl založen na dlouhodobem žihani vzorků a na jejich analýze metodou DTA.