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The SrTiO3 perovskites n-doped with Sm3+, Dy3+, and Nb5+ were prepared via the conventional solid state reaction route (SSR) followed by spark plasma sintering (SPS) process. The SPS in dynamic vacuum promotes formation of Ti3+ and Nb4+ species, as verified by the XPS analysis. Presence of the reduced cations, primarily Ti3+, is in agreement with the observed color changes and enhanced electrical conductivity of the samples. The Sr-site substitution by Sm and Dy is highly effective in phonon scattering and reducing the lattice thermal conductivity. Besides, this substitution significantly increases the electron mobility and electrical conductivity, by reducing the lattice strain imposed by the Ti/Nb substitution. Thermoelectric measurements indicated that a doubly doped sample with the Sr0.95Sm0.05Ti0.9Nb0.1O3 loading chemical composition reached the figure of merit (zT) value of 0.41 at 873 K. Such a high zT value originates primarily from a high carrier mobility of 24 cm2/V s and a low thermal conductivity of 2.4 W/m K.

Single crystals of three new compounds, Na

Metal complexes 1–9 have been synthesized by reacting the benzothiazole–pyrazole derivative ligands (L1, L2 and L3) with the metal precursors of ruthenium (Ru), rhodium (Rh) and iridium (Ir). The complexes have been isolated as cationic mononuclear N ∩ N chelating metal complexes having the general formula as [(arene)M(κ2(N∩N)-L)Cl]PF6 where L = L1, L2 and L3, M = Ru, Rh and Ir, arene = p-cymene, Cp*. Structural studies revealed the mode of binding of the ligands to the metal centers is through the nitrogen atom of the benzothiazole ring and the pyrazole nitrogen atom forming a five-membered ring. All these complexes were characterized by various spectroscopic techniques as well as by XRD analysis. These complexes, as well as the ligands, have been investigated for antibacterial and antioxidant activity studies where only a few of the complexes exhibited antibacterial activity against Gram-positive bacterial strains, i.e., Staphylococcus aureus and Bacillus thuringiensis with complex 6 showing the highest bacterial inhibition toward Staphylococcus aureus and complexes 3, 4 and 6 showing the highest inhibition toward Bacillus thuringiensis. While for the antioxidant activity study, all the compounds showed profound antioxidant potency with complexes 6 and 9 showing more the 50% DRSA activity with reference to ascorbic acid (100%) taken as a reference. The antioxidant activity of the complexes is more pronounced as compared to their respective ligands alone. Benzothiazole–pyrazole derivative ligands upon complexation with the halide bridged metal precursors resulted in the formation of mononuclear N ∩ N chelating complexes. These complexes have been investigated for biological studies such as antibacterial and antioxidant studies, and they arrayed potential response against the bacterial strains under study as well as good antioxidant activity.

Heavily Nb-doped strontium titanate (SrTi1-xNbxO3) nanoparticles and SrTi1-xNbxO3/TiO2 nanocomposite powders were synthesized by a sol-gel method. Structural characterization of the obtained powders was performed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and UV–visible spectroscopy. The powders were densified by spark plasma sintering (SPS) method up to 98% of the relative density. Upon composite production, the thermal conductivity of the un-doped samples was effectively decreased for SrTiO3/TiO2 nanocpmposite from 12 to 8 W/m.K. On the other hand, thermal conductivity of the Nb-doped SrTi0.8Nb0.2O3/TiO2 composite was decreased by about 50% down to 3.4 W/m.K in comparison to SrTiO3/TiO2 due to the phonon scattering at the point defects originated from both Nb atoms and TiO2 nanoparticles.

The current work provides a comparative study of the thermoelectric properties of the Sn0.5Ge0.5Te phases doped with Sb and Bi and alloyed with Cu2Te. The Sn0.5Ge0.5Te composition was chosen based on the fact that it delivers the highest ZT value within the Sn1−xGexTe series (x ≤ 0.5). Doping Sn0.5Ge0.5Te with electron-richer Sb and Bi improves both the charge transport properties and thermal conductivities. Alloying with Cu2Te optimizes the thermoelectric performance of the samples even further, yielding a ZT value of 0.99 for (Sn0.5Ge0.5)0.91Bi0.06Te(Cu2Te)0.05 at 500 °C. Hall measurements were performed to understand the effects of doping and alloying.

The Sr0.95Sm0.0125Dy0.0125□0.025Ti0.90Nb0.10O3±δ/ZrO2 composite was directly prepared through spark plasma sintering. This approach limited the grain growth and facilitated the achievement of a narrow grain size distribution due to fast sintering and ZrO2 effects. Thermal conductivity declined to 1.68 W m−1 K−1, which is the lowest among the reported values for micro-polycrystalline SrTiO3-based structures.

The Mn1.15Fe0.80P0.50Si0.50Cx compounds with x = 0, 0.01, 0.03, and 0.05 were prepared by twice solid-phase sintering and we investigated the changes of the structure and magnetocaloric properties by C doping. All samples are found to show Fe2P-type structure with minor impurity phase and some carbon atoms enter into Fe2P-type main phase and occupy the interstitial site. Carbon addition leads to an increase of the Curie temperature from 289 to 321 K and the thermal hysteresis has a reduction about 31.5%. All samples show distinct first-order magnetic transition. The peak value of magnetic entropy change and adiabatic temperature change is increased by 26% and 11% with addition of carbon under a low field of 0–2 T, respectively. The large magnetocaloric effect might be resulted from the latent heat of phase transition induced by temperature derived from calorimetric measurements. The results indicate that (Mn,Fe)2PSiC compound with large magnetocaloric effect is a good candidate for room temperature magnetic refrigeration.

The effect of structural disordering on the magnetic properties and magnetocaloric effect of amorphous (Gd4Co3)1–xGex (x = 0, 0.05, 0.10, 0.15) alloys is studied. The structure of the ribbons after melt-spinning is determined using an x-ray diffractometer. The thermal analysis is performed with the help of a differential scanning calorimeter. The temperature of the start of crystallization is determined. The magnetic properties are measured in a PPMS-9 system. The Curie temperature and the temperature dependence of the magnetization are determined. Different models are used for describing the critical exponents of the magnetic phase transitions.

The Mn1.2Fe0.8P0.6Si0.4B0.05 alloys were prepared by ball milling and melt-spinning methods. The structure and magnetic characteristics of all samples were examined by X-ray diffraction, vibrating sample magnetometer and SEM. Results show that both the ribbon and bulk alloys can crystallize in a hexagonal Fe2P-type phase with some impurity phase. The lattice parameters, a and c, of Fe2P-type phase are 6.02960 A, 6.03033 A, and 3.42310 A, 3.44431 A for ribbon and bulk Mn1.2Fe0.8P0.6Si0.4B0.05 alloys, respectively. The Curie temperature increased by 20% from 165 K in bulk to 197 K in ribbon while thermal hysteresis and magnetic hysteresis decreased by 28% and 80% for ribbon sample, respectively. Moreover, the values of magnetic entropy change can be tuned from 15.7 J⋅kg−1⋅K−1 in bulk to 21.8 J⋅kg−1⋅K−1 in ribbon under 0–5 T, resulting in the effective refrigerant capacity (RCE) increasing from 238 to 286 J⋅kg−1. The nature of the phase transitions was studied through the Arrott plots, indicating that the samples undergo first-order ferro-paramagnetic phase transitions. The origin of magnetic hysteresis losses is also discussed deeply. Furthermore, this alloys with large magnetic entropy change could be an interest potential for future magnetic refrigeration applications.

The composition of the In-substituted Zn13Sb10 phases follows the Zn13-1.5xInxSb10 charge-balanced formula and the reduction in the Zn content is due to the In3+ oxidation state, compared to the Zn2+ oxidation state. Zn deficiency in the In-doped samples is supported by the X-ray powder diffraction and EDS elemental analyses. Single-crystal X-ray diffraction refinement backs the Zn deficiency by revealing absence of Zn atoms in the interstitial sites and decreased occupancy of the main Zn site. The heat capacity measurements indicate that incorporation of In suppresses the α → α′ (235 K) and α′ → β (254 K) phase transitions, which could be due to the disappearance of some interstitial Zn atoms and/or difficulty in ordering the remaining ones. Both electrical resistivity and Seebeck coefficient data suggest a decrease in charge carrier concentration, stemming from an increased occupancy of the valence band. The thermal conductivity reveals changes in the phonon scattering pathways upon In doping; dominance of point defect scattering in Zn13-1.5xInxSb10 vs. Umklapp scattering in the pristine Zn13Sb10.

The crystal structure of new Lu14Co3In3-type {Gd, Tb, Lu}14Ni3Al3 compounds (P42/nmc. N 137, tP80) has been established using powder X-ray diffraction studies with cell parameters a = 0.95765(2) nm, c = 2.30214(5) nm for Gd14Ni3Al3, a = 0.95012(5) nm, c = 2.28190(10) nm for Tb14Ni3Al3 and a = 0.92604(2) nm, c = 2.23350(4) nm for Lu14Ni3Al3. Magnetic properties of the polycrystalline Y14Co3Al3, Gd14Co3.2Al2.8 and {Tb, Dy}14{Co, Ni}3Al3 have been studied by magnetization measurements. Y14Co3Al3 is paramagnetic down to 2 K, Gd14Co3.2Al2.8 exhibits ferro-antiferromagnetic ordering, while {Tb, Dy}14{Co, Ni}3Al3 show field sensitive pure antiferromagnetic ordering with field induced slight ferromagnetism. Heat capacity measurements (in zero applied magnetic field and field of 50 kOe) confirm metamagnetic-like transitions of Tb14Ni3Al3 and Dy14Ni3Al3.

The aim of this study was to investigate the effect of nickel and cobalt cations on magnetic properties of manganese-zinc ferrite (MZF) nanoparticles. The nanoparticles were produced through sol-gel combustion process with citric acid as the fuel. Then the obtained nanoparticles were calcinated for 30 min at 500 °C. In order to characterize the compounds, four methods were employed, including X-ray diffraction (XRD), vibrating sample magnetometer (VSM), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Spinel formation was confirmed by XRD and it was shown that the crystallite size in all samples was less than 12 nm (nm). In addition, FESEM images revealed that the nanoparticle size was less than 70 nm after calcination. Saturation magnetization (MS) and coercivity (HC) of the MZF nanoparticles are increased by adding Ni and Co cations.

The MnFeSixP1-x phases (x = 0.30, 0.35, 0.40, 0.48, 0.52, 0.54, 0.56) have been synthesized by arc-melting and subsequent high-temperature sintering. For the first time, single crystals of x = 0.30, 0.40 were successfully grown and analyzed by single crystal X-ray diffraction. Variable temperature X-ray diffraction experiments for x = 0.30 were completed and they show structural changes across the phase transition. Magnetization data revealed that the Curie temperatures and thermal hysteresis values can be tuned according to the Si:P ratio.

For high-performance thermoelectric material, spark plasma sintering (SPS) has been widely used to manufacture specimens in a very short period compared to other sintering techniques. However, the microstructural evolution, phase stability and compositional homogeneity of thermoelectric materials under SPS conditions have been rarely investigated. In this work, we studied the effect of SPS on microstructure, phase homogeneity and thermoelectric properties of the ternary Co4Ge6Te6 skutterudite. Phase homogeneity of the spark plasma sintered Co4Ge6Te6 pellets was investigated by X-ray microdiffraction and SEM/EDS analyses. Significant variations in the physical properties reflect presence of different crystalline phases due to the current-driven decomposition inside the samples. Use of the electrically insulating Mica film prevents the current from passing through the sample and yields high-quality samples. Furthermore, small amounts of Sb, added to investigate the role of dopants on the physical properties, yielded the highest power factors for the Co4Ge6Te6-based compounds.

SnTe, a lead-free chalcogenide-based material, shows potential to achieve high thermoelectric performance. This report presents a comparative study of different metallic dopants in SnTe and their effect on its microstructures, and mechanical and thermoelectric properties. Doped SnTe (Sn1−xAxTe, A = Co, Ni, Zn, Ge, and x = 0.01, 0.03, 0.05) materials are prepared by melting–quenching synthesis followed by spark plasma sintering. X-ray powder diffraction analysis showed that the solubility of Co, Ni, and Zn in the structure is in the range from 0 to 0.01; however, Ge can be doped in higher amounts. The back-scattered electron images and elemental maps revealed that the CoTe, Ni3SnTe2 and ZnTe impurity phases precipitate on the grain boundaries in the SnTe matrix. Ge-doped samples have more uniform microstructures with a very few Ge-rich regions, which implies higher Ge solubility in agreement with the XRD results. The existence of impurity phases in the Co-, Ni-, and Zn-doped samples yields lower lattice thermal conductivities without deterioration in charge transport properties, leading to higher ZT values relative to the pristine SnTe sample. The microhardness of the doped samples is also improved due to the crack growth suppression and crack branching.

The current work provides a comparative study of the thermoelectric properties of the Sn

The Sr

Gd(Co1-xGax)2 (x = 0, 1/6, 1/3, 1/2, 2/3, 5/6, and 1) phases were synthesized by arc melting the constituent elements and subsequent annealing. The samples were characterized by powder and single crystal X-ray diffraction, magnetic measurements, and electronic structure calculations. An interesting structural sequence was obtained: cubic MgCu2-type structure for x = 0 and 1/6; MgZn2-type structure for x = 1/3; orthorhombic SrMgSi-type structure for x = ½; orthorhombic CeCu2-type structure for x = 2/3; hexagonal AlB2-type structure for x = 5/6 and 1. Tight-binding linear-muffin-tin orbital (TB-LMTO) calculations were performed on GdCo2, GdCoGa, and GdGa2 to trace the origin of their structural transformations, which appear to be driven by the changes in the valence electron count (VEC). In addition, some conclusions of these fully stoichiometric compounds were obtained from the rigid band model. GdGa2 (x = 1) is antiferromagnetic, while the other ones are either ferrimagnetic or ferromagnetic. TC of Gd(Co1-xGax)2 decreases monotonically with the increasing Ga content, suggesting that promising room temperature (RT) magnetocaloric materials could be obtained between x = 1/6 and x = 1/3.

Half-sandwich organometallic rhodium and iridium complexes [1–6] have been synthesized with ligands L1 (L1 = Pyridin-2-ylmethylene picolinichydrazine) and L2 (L2 = Pyridin-3-ylmethylene picolinichydrazine). Treatment of [{Cp∗MCl2}2] (M = Rh/Ir) with L1 in methanol has yielded mononuclear cationic complexes such as [{Cp∗M(L1N∩N)Cl}]PF6 where {M = Rh (1) and Ir (2)} and dinuclear complexes such as [{(Cp∗MCl)2(L1N∩N, N∩N)}]PF6 where {M = Rh (3) and Ir (4)} in 1:2 and 1:1 metal dimer to ligand ratios respectively. Reactions of [{Cp∗MCl2}2] with L2 in both 1:2 and 1:1 metal dimer to ligand ratios have yielded two metalla-macrocyclic dinuclear and dicationic complexes such as [{Cp∗M(L2N∩NμN)}2](PF6)2 where {M = Rh (5) and Ir (6)}. Spectroscopic and crystallographic data were used to elucidate the structures of the synthesized complexes. The in vitro antitumor evaluation of the complexes 1 and 2 by fluorescence based apoptosis study revealed their antitumor activity against Dalton’s ascites lymphoma (DL) cells. The antibacterial evaluation of complexes 1, 2, 5 and 6 by agar well-diffusion method revealed their significant activity against the two species considered viz., Proteus vulgaris (MTCC 426) and Vibrio parahaemolyticus (MTCC 451) with zone of inhibition up to 43 mm. The docking study with few key enzymes associated with cancer viz., ribonucleotide reductase, thymidylate synthase, thymidylate phosphorylase and topoisomerase II revealed their strong interactions with complexes under study. Complexes 1–6 exhibited a HOMO (highest occupied molecular orbital) – LUMO (lowest unoccupied molecular orbital) energy gap from 2.95 eV to 3.59 eV. TDDFT calculations explain the nature of electronic transitions and found well agreement with the experiments. Keywords: Rhodium dimer, Pyridin-2-ylmethylene picolinichydrazine, Metalla-macrocycles, Antitumor, Antibacterial, TDDFT

The Gd-Co-Al system has been investigated at 870/1070 K by X-ray and elemental EDS analyses. The existence of the known compounds Gd2Co3Al9 (Y2Co3Ga9-type), Gd3Co4.5Al11.5 (Gd3Co4.6Al11) (Gd3Ru4Al12-type), Gd3Co6–7.4Al3–1.6 (CeNi3-type), GdCo1.15–0.65Al0.85–1.35 (MgZn2-type), Gd2Co2Al (Mo2NiB2-type) and Gd3Co3.5–3.25Al0.5–0.75 (W3CoB3-type) has been confirmed at 870/1070 K. Structure types have been determined for Gd2Co6Al19 (U2Co6Al19-type), Gd7Co6Al7 (Pr7Co6Al7-type), Gd6Co2–2.21Al1–0.79 (Ho6Co2Ga-type) and Gd14Co3.2Al2.8 (Gd14Co2.58Al3.42 at 970 K) (Lu14Co3In3-type). The structures of Gd6Co2Al, Gd6Co2.21Al0.79 and Gd14Co2.58Al3.42 flux-grown at 970 K have been refined from the single crystal X-ray diffraction data. Additionally, new ternary compounds Gd2Co5.7–5.3Al1.3–1.7 (Er2Co7-type) and ~Gd58Co20Al22 (unknown type structure) have been identified. Quasi-binary solid solutions were detected for Gd2Co17, GdCo5, Gd2Co7, GdCo3, GdCo2 and GdAl2 at 870/1070 K, while no appreciable solubility was observed for the other binary compounds in the Gd-Co-Al system. Magnetic properties of the Gd2Co3Al9, Gd3Co4.6Al11, Gd7Co6Al7, Gd6Co2.2Al0.8 and Gd14Co2.58Al3.42 compounds have been studied and are presented in this work. Gd6Co2.2Al0.8, Gd3Co4.6Al11, Gd7Co6Al7 and Gd14Co2.58Al3.42 order ferromagnetically, while Gd2Co3Al9 displays antiferromagnetic transition. Additionally, {Y, Sm, Tb - Tm}2Co6Al19 (U2Co6Al19-type), Yb2Co3Al9 (Y2Co3Ga9-type), {Y, Sm, Tm, Yb}3Co4.6Al11 (Gd3Ru4Al12-type) and Tb7Co6Al7 (Pr7Co6Al7-type) compounds have been synthesized and investigated.

The Zn–Sb system contains two well-known thermoelectric materials, Zn1−δSb and Zn13−δSb10 (“Zn4Sb3”), and two other phases, Zn9−δSb7 and Zn3−δSb2, stable only at high temperatures. The current work presents the updated phases diagram constructed using the high-temperature diffraction studies and elemental analysis. All phases are slightly Zn deficient with respect to their stoichiometric compositions, which is consistent with their p-type charge transport properties. Either at room or elevated temperatures, Zn1−δSb and Zn13−δSb10 display deficiencies of the main Zn sites and partial Zn occupancy of the other interstitial sites. A phase pure Zn13−δSb10 sample can be obtained from the Zn13Sb10 loading composition, and there is no need to use a Zn-richer composition such as Zn4Sb3. While the Zn13−δSb10 phase is stable till its decomposition temperature of 515 °C, it may incorporate some additional Zn around 412 °C, if elemental Zn is present.

RE (Co 0.667 Ga 0.333 ) 2 ( RE = Ho, Er) were characterized by neutron powder diffraction (NPD). Rietveld refinement of the NPD data at 280 K confirms the hexagonal MgZn 2 -type structure ( P 6 3 /mmc ), in accordance with the previous XRD results. Co/Ga occupancies on the 2 a and 6 h sites were refined to be 0.46/0.54(2) and 0.74/0.26(2), respectively, indicating a preference of Ga for the 2 a site and of Co for the 6 h site. Both materials are ferromagnetic, k = (000), with measureable moments only on the RE sites. The magnetic (Shubnikov) space group is P 6 3 / mm′c′ for the Er phase. Co moments refined to values of 0.1–0.3 μ B and are effectively zero within 3σ. The Er moment, 6.07(8) μ B at 3.5 K is parallel to the c axis and this orientation persists up to T C = 18.5 K, while the Ho moment has components along both the a and c axes with a total moment of 6.3(1) μ B at 3.5 K. Both moments are much reduced from the free ion values, 9 μ B (Er) and 10 μ B (Ho), which is attributed to crystal field effects. In addition, the Ho moment angle with the c axis is strongly temperature dependent, being roughly constant, ~ 24(6)° from T = 29 K to ~25 K, then increasing with decreasing temperature to 44(1)° at 3.5 K. Magnetic small angle neutron scattering (MSANS) was observed over a Q -range from 0.14 A −1 to 0.50 A −1 in both samples. The integrated MSANS of the Er phase peaks near T C , then decreases monotonically with decreasing temperature, behavior typical for a simple ferromagnet. On the other hand, the integrated MSANS for the Ho phase exhibits a weak peak around T C = 31 K, followed by a plateau to 25 K and a strong increase with decreasing temperatures, which tracks the evolution of the Ho moment angle with the c axis.

Structures of two new phases, Na2BaGe8O18 (1) and Rb2BaGe8O18 (2), were determined by single crystal X-ray diffraction. The phases are isostructural and crystallize with the P 3 ¯ c1 space group. The new octagermanates are built from the 3D anionic germanate frameworks, with alkali and alkaline earth cations located in their channels. The frameworks are made by corner-sharing GeO4 and GeO6 polyhedra. The way the GeOn polyhedra are connected in Na2BaGe8O18 (1) and Rb2BaGe8O18 (2) demonstrates a specific topology different from the related compounds. The patrial doping of the octahedral Ge sites in Rb2BaGe8O18 (2) with Mn4+ yielded a series of red-emitting phosphors. The photoluminescent data for these phosphors were collected and the highest phosphorescence intensity was found in the Rb2BaGe7.995O18: 0.005Mn4+ sample.

Rare-earth-based pnictide oxides (RE,Ca)mPnnOm (Pn = Sb, Bi) adopt a variety of interrelated structures based on specific stacking sequences of rare-earth oxide sublattices. These phases are all prepared via high temperature reactions and may be selectively produced in high purity. X-ray single crystal studies also revealed the disorder of pnictogen atoms in the non-charge balanced structures, which gives rise to unexpected physical properties. It is theorized that Anderson localization of the Pn p states results in an activation energy which forces semiconductor-type behavior in these phases. Interestingly, the extent of the localization of states is directly dependent on the magnitude of the disorder of the pnictogen atom, which also depends on pnictogen and/or the rare-earth atom that is used. By altering the composition of the sample with respect to the choice of Pn and/or RE, the physical properties of these select phases may be tuned to the desirable level without a change to the overall structure. ...

Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys were prepared by copper mold suction casting method. Subsequent annealing processes were employed to tune the microstructures and magnetocaloric effects. Results show that Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys crystallize in a hexagonal phase with the Fe 2 P structure type. With increasing annealing temperature, the lattice parameters of a and c of Fe 2 P-type phase increase from 5.7988(1)A to 6.0785(2)A and from 3.3218(1)A to 3.4727(2)A for the Mn 1.15 Fe 0.85 P 0.50 Si 0.45 B 0.05 alloys according to XRD. At the same time the Curie temperature and magnetic entropy change increase from 233 K to 244 K and from 8.8 J kg −1 K −1 to 17.0 J kg −1 K −1 (Δ H = 2 T), respectively, while the thermal hysteresis decreases. The entropy changes of these alloys are also estimated from the Clausius-Clapeyron equation, Landau theory and heat capacity, respectively. The nature of the phase transitions were studied through the Arrott plots, which indicate that the samples undergo first-order ferro-paramagnetic phase transitions. However, the universal curve of scaled magnetic entropy change reveals that during the magnetic phase transition, there exists a critical magnetic field, about 1.25 T, below which the sample undergoes a second-order phase transition and above which it displays a first-order phase transition. Furthermore, mechanisms for the large magnetic entropy change and possibilities for the room-temperature magnetic refrigeration are discussed.

Several new MgZn2-type Laves phases with the P63/mmc symmetry and RE(Co0.667Ga0.333)2 stoichiometries (RE = Gd, Tb, Dy, Ho, and Er) were obtained by arc-melting and subsequent annealing. Single crystals with the MgZn2-type structure were extracted from the annealed RE(Co0.667Ga0.333)2 (RE = Gd, Tb, Dy, and Ho) alloys and Ga flux-grown Er(Co0.667Ga0.333)2 sample. Powder and single-crystal X-ray diffraction methods were used for the phase analysis and structural characterization. A decrease in the cell volume due to the lanthanide contraction is observed from Gd(Co0.667Ga0.333)2 to Er(Co0.667Ga0.333)2. RE atoms occupy the 4f site, while Co and Ga are in the 2a and 6h sites. Magnetic behavior of the hexagonal MgZn2-type RE(Co0.667Ga0.333)2 phases strongly depends on the RE. Apparent ferromagnetic transition is observed for RE = Gd, Tb, and Dy, while the other two phases (RE = Ho, and Er) seem to be ferrimagnetic. Magnetocaloric properties of the Gd(Co0.667Ga0.333)2 phase were measured; the small isothermal magnetic entropy change (ΔSiso) value of −4.94 J/kgK at 152 K and for a ΔH = 0–50 kOe field change suggests a conventional magnetocaloric effect.

Tin germanium tellurides, (SnGe)Te, are developed as a potential substitute for the lead telluride (PbTe) for thermoelectric power generation. SnTe and PbTe share similar crystal and electronic structures, however, SnTe has a much higher lattice thermal conductivity and a much lower Seebeck coefficient. Alloying SnTe with Ge and doping with other elements significantly improves its performance. This work provides a comparative study of the thermoelectric properties for the Sn0.5Ge0.5Te phases doped with In, and subsequently with Zn, Sb and Bi. The In doping on the Sn/Ge site induces resonant levels around the Fermi level, and thus, enhances the thermopower. Further doping with Sb and Bi in (Sn0.5Ge0.5)0.98In0.2Te leads to the valence band convergence (thus increasing the thermopower) and also optimizes the thermal conductivity. Comparison of the results for (Sn0.5Ge0.5)0.89In0.02Bi0.06Te and pristine SnTe reveal significant improvements in the average and highest ZT values by 446% (0.71 vs. 0.13) and 125% (0.80 vs. 0.36), respectively, within 100–500 ​°C.

Zn–Sb compounds (e.g., ZnSb, β-Zn13Sb10) are known to have intriguing thermoelectric properties, but studies of the Zn3Sb2 composition are largely absent. In this work, α-Zn3Sb2 was synthesized and studied via temperature-dependent synchrotron powder diffraction. The α-Zn3Sb2 phase undergoes a phase transformation to the β form at 425 °C, which is stable until melting at 590 °C. Rapid quenching was successful in stabilizing the α phase at room temperature, although all attempts to quench β-Zn3Sb2 were unsuccessful. The structure of α-Zn3Sb2 was solved using single crystal diffraction techniques and verified through Rietveld refinement of the powder data. α-Zn3Sb2 adopts a large hexagonal cell (R 3 space group, a = 15.212(2), c = 74.83(2) A) containing a well-defined framework of isolated Sb3– anions but highly disordered Zn2+ cations. Dense ingots of both the α-Zn3Sb2 and β-Zn13Sb10 phases were formed and used to characterize and compare the low temperature thermoelectric properties. Resistivity and Seeb...

A conventional solid-state approach has been developed for the synthesis of phase-pure magnetocaloric Mn2–xFexSi0.5P0.5 materials (x = 0.6, 0.7, 0.8, 0.9). Annealing at high temperatures followed by dwelling at lower temperatures is essential to obtain pure samples with x = 0.7, 0.8, and 0.9. Structural features of the samples with x = 0.6 and 0.9 were analyzed as a function of temperature via synchrotron powder diffraction. The Curie temperature, temperature hysteresis, and magnetic entropy change were established from the magnetic measurements. According to the diffraction and magnetization data, all samples undergo a first-order magnetostructural transition, but the first-order nature becomes less pronounced for samples that are more Mn rich.

Pentamethylcyclopentadienyl iridium(III) and rhodium(III) complexes of formulation [(η 5-C 5Me 5)M{(C 5 H 4N) 2 C=NR)}Cl]PF 6 were prepared by the reaction of [MCl 2(η 5-C 5Me 5)] 2(M = Ir or Rh) with dipyridyl-N-alkylimine ligands, (C 5 H 4N) 2 C=NR (R = Me or Et) in the presence of NH 4 PF 6 at room temperature. The reaction also produced an unexpected dipyridyl-NH-ketimine organometallic compound [(η 5-C 5Me 5)M {(C 5 H 4N) 2 C=NH}Cl]PF 6 as minor product when the reaction was performed under refluxing acetonitrile. The NH-ketimine compounds were formed via N-C single bond cleavage of imine ligand resulting in coordination of the transformed ligand, (C 5 H 4N) 2 C=NH to the metal centre. Complexes were obtained as their hexafluorophosphate salts and characterized based on IR, NMR and ESI-MS spectroscopic data. Authenticity of NH-ketimine organometallic compound was established by single crystal X-ray analysis of a representative compound, which crystallized in orthorhombic space group Pbcn and has a pseudo-octahedral geometry around the metal ion.

Hot extrusion is employed to produce bulk ZnSb and Zn13Sb10 thermoelectric materials. The extrusion parameters are optimized to achieve high purity products with high density and acceptable mechanical strength for further fabrication processing. Microstructural analysis is performed to investigate the products. X-ray diffraction, energy dispersive X-ray spectroscopy, and differential scanning calorimetry show high stability of the ZnSb phase during the extrusion that lead to high purity products. However, the Zn13Sb10 compound decomposes during the extrusion, yielding a bulk sample consisting of several other phases. Hot extrusion shows a great potential for scaled up production of high quality ZnSb thermoelectric materials.

A new compound, Mg3Ge1-δO4(1-δ)F2(1+2δ) was obtained by high temperature solid state reactions and flux method and its structure was characterized by single crystal X-ray diffraction. The structure relates to the silicate mineral norbergite, Mg3SiO4(OH)F, a member of the humite mineral group. The diffraction experiment revealed a deficiency of the Ge site in the new structure, which can be compensated by the substitution of either OH− groups or F− anions for O2− anions. The combination of the NMR, neutron scattering, and IR spectroscopy experiments suggest that the F− substitution is most likely; thus, the Mg3Ge1-δO4(1-δ)F2(1+2δ) formula is suggested. The F− substitution is present for the side product of the Mg3Ge1-δO4(1-δ)F2(1+2δ) synthesis, the compound known as Mg28Ge7.5O38F10. Refinement of the twined Mg28Ge7.5O38F10 crystal showed a slightly higher Ge content and the final composition was assigned as Mg28Ge8O40F8. The PbF2 flux method yielded a new compound, Mg2Pb2Ge2O7F2. The structure of this digermanate is related to the group of naturally occurring and synthetic silicates containing R3+ cations. High-temperature powder XRD experiments showed that the Mg3Ge1-δO4(1-δ)F2(1+2δ) phase cannot be synthesized from Mg2GeO4 and MgF2 in air due to the transformation of magnesium fluoride into MgO.

The Ca2RE7Pn5O5 phases (RE=Pr, Sm, Gd, Dy; Pn=Sb, Bi) were successfully prepared from high temperature reactions at 1225–1300 °C. These phases maintain the same structure types as the parent RE9Pn5O5 phases, except for a Ca/RE mixing. The study and preparation of these phases was motivated by the desire to shift the metallic type properties of the parent RE9Pn5O5 phases to a level more suitable for thermoelectric applications. Electrical resistivity measurements performed on pure, bulk samples indicated all phases to be narrow band gap semiconductors or semimetals, supporting the charge balanced electron count of the Ca2RE7Pn5O5 composition. Unfortunately, all samples are too electrically resistive for any potential usage as thermoelectrics. Electronic band structure calculations performed on idealized RE9Pn5O5 structures revealed the presence of a pseudogap at the Fermi level, which is consistent with the observed electrical resistivity and Seebeck coefficient behavior.

AlFe2B2 and AlFe2–xCoxB2 (x = 0–0.30) were synthesized from the elements in three different ways. The samples were characterized by powder X-ray diffraction, Rietveld refinements, energy-dispersive X-ray spectroscopy, and magnetic measurements. Using Al flux the formation of AlFe2B2 single crystals is preferred. Arc melting enables the substitution of ∼6% Co. This substitution of Fe by Co decreases the Curie temperature TC from 290 to 240 K. The highest Co substitution up to 15% is achieved by spark plasma sintering (SPS). TC is reduced to 205 K. In all cases an excess of Al is necessary to avoid the formation of ferromagnetic FeB. Al13Fe4–xCox is the common byproduct. TC and the cobalt content are linearly correlated. The transition paramagnetic–ferromagnetic remains sharp for all examples. The magnetic entropy change of the Co-containing samples is comparable to AlFe2B2. SPS synthesis yields, in short reaction times, a homogeneous and dense material with small amounts of paramagnetic Al13Fe4–xCox as an ...

A facile chemical method for the synthesis of 3C–SiC nanoflakes is presented. The process involves the pyrolysis of polycarbosilane (PCS) at 700 °C, in a NaCl powder template, followed by thermal treatment at 1200 °C. The salt is easily removed by washing with water. The morphology of the SiC particles is found to be dependent on the NaCl/PCS weight ratio and by carefully tuning this ratio, different SiC structures can be obtained. While at NaCl/PCS ratios < 40 : 1 micrometer-sized particles with a foamy like structure result, a NaCl/PCS ratio of 40 : 1 is crucial for the formation of 3C–SiC nanoflakes. These nanoflakes are less than 5 nanometers thick, have a high specific surface area of 169 m2 g−1 and a high total pore volume of up to 0.75 cm3 g−1. This method could open a simple, versatile and robust way for the production of SiC nanostructures. Such a facile synthetic method could bring nanostructured SiC one step closer to the ultimate goal of practical applications.

The second and third known rare-earth bismuthide oxides, Gd3BiO3 and Gd8Bi3O8, have been discovered via high temperature reactions at 1300 °C. Like its Gd–Sb–O counterparts, the Gd3BiO3 and Gd8Bi3O8 phases crystallize in the monoclinic C2/m space group, with the latter containing disordered Bi atoms along the b direction of the unit cell. Unlike the RE8Sb3O8 series, the formation of the Gd3BiO3 phase does not necessarily precede the formation of Gd8Bi3O8, which is likely due to the difficulty of accommodating bismuth in the RE–O framework due to its larger size. Physical property measurements performed on a pure Gd8Bi3O8 sample reveal semiconducting behavior. Although electronic structure calculations predict metallic behavior due to an unbalanced electron count, the semiconducting behavior originates from the Anderson localization of the Bi p states near the Fermi level as a result of atomic disorder.