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Thermoelectric (TE) Cu3SbS3, as one of the Cu–Sb–S families, has the characteristic of strong anharmonicity of lattice vibrations. It may be a potential replacement for the unstable pristine tetrahedrite, provided that its cubic structure can be stabilised. In this study, pristine (near)-phase-pure cubic Cu3SbS3 and Fe-doped samples were successfully prepared by sequential use of equilibrium and non-equilibrium synthesis techniques. TE properties of both pristine and doped samples were optimised by tuning the sintering parameters. A maximum zT of 0.57 was achieved at 350 °C in pristine (near)-phase-pure cubic Cu3SbS3 sample hot pressed at 575 °C for 30 min, which is about 2.7 times higher than that of the spark plasma sintered one. The Fe-doped sample sintered at 575 °C for 45 min displays a higher zT in the whole testing temperature range and a maximum of 0.62 was reached at 350 °C. The influences of hot pressing and spark plasma sintering on the phase structure, microstructure, thermodynamic and TE properties were studied and correlated. The results demonstrated the potential of cubic Cu3SbS3 as a high-performance material.

Tb1–xTmxFeO3 (x = 0.00, 0.15, 0.25) polycrystalline series were synthesized using a solid-state reaction. Our results show that all three prepared samples are in a distorted orthogonal structure and their space group is p b n m . When the Tm3+ doping amount increases, the characteristics of the spin-flip of the sample decreases following an initial increase at the beginning; the antiferromagnetic property almost reaches zero; the magnetization decreases at the beginning but increases later on. The maximum magnetic entropy change and magnetic refrigeration effect RCP are reduced at varying degrees. Under a 7 T magnetic field, the maximum magnetic entropy change, ΔSmax, for the three samples of Tb1–xTmxFeO3 with x = 0.00, 0.15, 0.25 is 13.78, −9.28, and 10.69 J/(K·kg), respectively; the magnetic refrigeration capacity (RCP) is 316.85, 175.2, and 297.60 J/kg, respectively. In summary, doping with the element Tm reduces ΔSmax and RCP of the sample. Since the maximum magnetic entropy change and the cooling capacity for the three samples are relatively large, they can be used as an alternative for magnetic refrigerants.

Misfit-layered Ca3Co4O9 as a p-type semiconductor is difficult to commercialize because of its relatively poor performance. Here, Ca2.7-xLaxAg0.3Co4O9/Ag composites prepared by spark plasma sintering were systematically investigated in terms of La3+ dopant levels and nano-sized Ag compacts. Multiscale microstructures of stacking fault, dislocation, and oxygen vacancy-linked defects could be recognized as an effective strategy for tuning the transport of charge carriers and phonon scattering. An increasing concentration of charge carriers was caused by the introduction of nano-sized Ag particles at the grain boundary. The multiscale structural defects served as phonon scattering centers to reduce the thermal conductivity. Finally, the Ca2.61La0.09Ag0.3Co4O9/Ag sample exhibited a maximum ZT of 0.35 at 1073 K. The results suggest that the interplay of structural defects provides an impetus for a huge improvement in thermoelectric performance.

Recently, PbSe has attracted extensive attention as an excellent thermoelectric material, which is considered as an alternative for PbTe. In this paper, single-phase PbSe was rapidly synthesized by mechanical alloying followed by high-pressure sintering method. The effect of sintering temperature on the thermoelectric properties of PbSe has been investigated. The resistivity, Seebeck coefficient, and phonon thermal conductivity of PbSe decrease with the increasing sintering temperature due to the formation of native defects during HPS process. The maximum figure of merit ZT value of ~ 0.57 at 600 K was achieved for the sample sintered at 1200 K, which is much higher than that of polycrystalline PbSe around this temperature prepared by other methods. These results indicate that combining with MA and HPS is a simple, energy-saving, and effective method to synthesize and tune the thermoelectric properties for PbSe.

The commercial application of Ca3Co4O9 ceramics at high temperatures is greatly restricted due to poor thermoelectric properties. One of the approaches to enhance the performance of oxide thermoelectric ceramics is to control the microstructure of the ceramics to provide texturing. Herein, a high figure of merit of ZT = 0.43 was reported at 1073 K for the highly grain-oriented (Ca0.87La0.03Ag0.1)3Co4O9 ceramics, which were fabricated by tape casting combined with templated grain growth. Multi-scale interfaces, such as the parallel grain boundary and regular zigzag edge, the “core–shell” interface inside the stripe-like grain orientation, and lattice stack default, were observed in the “brick-wall” microstructure. The electron transport properties and thermal conductivity in different directions were investigated during the texture evolution, which was regulated by increasing the sintering temperature. By adjusting the sintering temperature, the sample parallel to the tape-casting direction showed a maximum power factor of 0.64 mW (m−1 K−2) as a result of effective interfacial effects, which was ∼3 times higher than that in the perpendicular direction. The ultralow thermal conductivity of 0.366 W (m−1 K−1) at 1073 K was obtained because phonon scattering was strengthened through the “core–shell” interface and zigzag interface. This work provides a new insight to achieving high-performance thermoelectric oxides using an interesting interface modulation and anisotropic properties through texture engineering.

The zeolitic imidazolate framework-8 (ZIF-8), as a kind of MOF, is widely used in sensors, gas storage/separation, drug delivery, and catalysis due to its adjustable porous structure, high surface area, and excellent chemistry tunability. ZIF-8 is constructed by Zn2+ and 2-methylimidazole and synthesized in the methanol solution. In this paper, we explored the influence of the reused methanol solution for the structure and properties of the synthesized ZIF-8. The as-synthesized ZIF-8 was characterized by an X-ray diffraction instrument (XRD), a scanning electron microscope (SEM), a specific surface area analyzer (BET), and Fourier transform infrared spectroscopy (FT-IR). The results show that the reused methanol solution does not change the phase, porous structure, and BET surface area of ZIF-8. However, the particle size of ZIF-8 increases from 50 nm to 5 um and the productive rate decreases to 7.4% when the methanol solution is reused four times. This work provides new insight into the reuse of dissolvents for the synthesis of MOFs.

In this paper, p-type thermoelectric material Te–Se solid solutions have been successfully prepared by the high-pressure technique. The thermal conductivity of Te was depressed sharply by Se alloying. An extremely low thermal conductivity ∼0.27 W m−1 K−1 was obtained for Te alloyed with 15 mol% Se, which near the theoretical minimum, κ min . The bipolar diffusion effect of Te was suppressed by Se alloying due to the increased band gap, which lead to enhanced Seebeck coefficient and depressed bipolar diffusion thermal conductivity under high temperature. The maximum figure of merit, ZT of 0.37 at 480 K was obtained for Te alloyed with 5 mol% Se, which is about twice higher than that of pristine Te.

The n-type semiconductor large single diamonds with S doping and B-S co-doping were successfully synthesized in FeNi-C system at the constant conditions about temperature 1250 °C and pressure 5.6 GPa. In this study, the effects of different additive amounts of FeS doping alone and B-FeS co-doping on the crystal shape, crystal face, color and quality of diamonds were investigated. The influence of B-FeS co-doping on the V-shaped region of diamond growth is greater than that of FeS-doping diamond. The color of FeS doping crystals change from bright yellow to bright green and then appear grayish yellow. On the contrast, the color of B-FeS co-doping diamond changes from yellowish green to grayish green and black. We found that our obtained diamond contains B/S/N elements, and S exists in C-S-O forms in diamond lattice. Besides, as the increasing amount of additive B, the content of S/N relative to C is also improved. FeS instead of S as an additive is more conducive to incorporation of S into diamond than that in previous studies. The results of Hall Effect measurement showed that diamonds with FeS single-doping and B-FeS co-doping are n-type semiconductors. B-FeS co-doping not only contributes to improvement Hall mobility and carrier density but the reduction of resistance in diamond. The previous study of the first-principles calculation for n-type B-S co-doping and S-doping diamond was verified experimentally by synthesizing FeS-doping and B-FeS co-doping large single crystal diamonds in this paper. This work helps to further understand the mechanism of the synthesis and electrical properties of B-FeS co-doping and FeS single-doping diamond.

Dense TiB2 TiC composites were synthesized by high pressure method at 5.5 GPa and 1400–1800 °C with pure Ti and B4C powders as raw materials. The phase composition, density, microstructure, hardness and thermal conductivity of TiB2 TiC composites were analyzed. The results indicated that, the formation of intermediate phases were strongly depended on the synthesis temperature. TiB2 TiC composites prepared under high pressure condition had a dense microstructure without obvious pores, which could achieve the bulk density and the relative density about 4.40–4.57 g/cm3 and 95.1%–98.7%. Vickers hardness values was up to 22.1–30.1 GPa with the load of 4.9 N and 20.3–28.9 GPa with the load of 9.8 N. Thermal conductivity of the TiB2 TiC composites was measured to be 51.2–74.5 W/m−1 K−1. The density and grain size of the TiB2 TiC composites changed with the increase of temperature, leading to the change of hardness and thermal conductivity.

We demonstrate the use of elemental precursors Cu, Fe, Sn, and S to obtain a mawsonite (Cu6Fe2SnS8)/stannite (Cu2FeSnS4) composite using a solid-state process at ambient temperature in an industrial eccentric vibration mill for up to 240 min in argon atmosphere. The samples were characterized using various analytical techniques such as x-ray diffractometry, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and nitrogen adsorption and magnetic measurements. For thermoelectric measurements, the properties of samples densified via spark plasma sintering were measured using standard methods needed to calculate the figure of merit. The transformation of elemental precursors to a composite mixture proceeds relatively rapidly via several intermediate steps. The kinetics of this transformation is also in good agreement with the results for the unconsumed sulfur content in the reaction mixtures and can also be correlated with the magnetization results. Based on the thermoelectric measurements of the sample milled for 240 min, the calculated figure of merit reached a value of zT = 0.51 at 623 K due to a very low lattice thermal conductivity of 0.29 W/m-K and moderate power factor of 3.3 μW/cm-K2. The thermoelectric results obtained for the material are comparable to previously published values for pure mawsonite prepared from elements by laboratory ball milling.

BiCuSeO based oxide show excellent thermoelectric performance due to its low thermal conductivity and moderate Power factor. There is rare study on the same crystal structured BiCuSO with lower cost and more earth abundance. The thermoelectric performance of BiCuSO is limited by its high resistivity result from its low carrier concentration and large band gap. In this paper, p-type polycrystalline BiCuSO doped with Pb was fast prepared by one-step high pressure method and the composition dependent thermoelectric properties was studied. The electrical resistivity and Seebeck coefficient of Bi1-xPbxCuSO both decreased monotonically with increasing Pb content due to the increased carrier concentration. The power factor was improved and the thermal conductivity was suppressed by Pb doping. The maximum figure of merit, ZT∼0.14 @ 700 K was obtained for the Bi0.975Pb0.025CuSO sample, which makes them promising candidates for thermoelectric applications.

Besides high thermoelectric (TE) performance, simple chemical compositions and facile synthesis methods are attractive for practical fabrication and applications of TE materials due to their effective rates of synthesis and higher stabilities. Element semiconductor Tellurium (Te) is one potential middle temperature TE material and has attracted wide interest in material science. In this study, we report that a high thermoelectric performance ZT ~ 0.88@600 K for polycrystalline Te with slight Antimony (Sb) doping was facile synthesized by one-step high pressure technique. Our experimental results reveal that the carrier concentration of high pressure synthesized Te is more sensitive to dopants compared with the samples obtained by the conventional preparation method. We observed large amount of nanograins, second nano-phase and crystal defects in the high pressure synthetic samples, which can significantly weaken the phonon thermal conductivity, leading to a high TE performance in Te samples. This work indicates that high pressure method provides an alternative direction for designing TE materials with simple composition.

We present the work about the initiative fabrication of multi-scale hierarchical TiO2-x by our strategy, combining high pressure and high temperature (HPHT) reactive sintering with appropriate ratio of coarse Ti to nanosized TiO2. Ubiquitous lattice defects engineering has also been achieved in our samples by HPHT. The thermoelectric performance was significantly enhanced, and rather low thermal conductivity (1.60 W m−1 K−1) for titanium oxide was reported here for TiO1.76. Correspondingly, a high dimensionless figure of merit (zT) up to 0.33 at 700 °C was realized in it. As far as we know, this value is an enhancement of 43% of the ever best result about nonstoichiometric TiO2 and the result is also exciting for oxide thermoelectric materials. The moderate power factor, the significantly reduced thermal conductivity and the remarkable synergy between electrical properties and thermal conductivity are responsible for the excellent thermoelectric performance. We develop a facile strategy for preparing multi-scale hierarchical TiO2-x and its superior ability to optimize thermoelectric performance has been demonstrated here.

This paper reported the synthesis of slab shape diamond crystals with phosphorus doping from FeNiMnCo-C system in cubic anvil high pressure apparatus (SPD-6 × 1200) at 5.6 GPa and 1250–1320 °C. It was attributed to the presence of additive phosphorus that the temperature region of synthetic sheet cubic diamond increases evidently. With the increase of phosphorus content, the surfaces of the slab shape diamond crystals became rough. The results of Raman spectroscopy indicated that the diamonds doped by more phosphorous have more crystal defects and impurities. Furthermore, the electrical properties of the large diamond crystals were tested by a four-point probe and the Hall Effect method. It was shown that the large single crystal samples were n-type semiconductors. This work enriches the application of the slab large diamond crystals.

Large single-crystal diamonds with n -type semiconductor were synthesized from S/B-S co-doping FeNiCo-C system under high pressure and high temperature (HPHT) in this paper. It was found that the slight variation of the additive S content had not made obvious change for the color of diamonds synthesized from FeNiCo-C system. The B-S co-doping samples became more transparent and yellow than the samples added alone by S. The analysis of X-ray photoelectron spectroscopy (XPS) spectra and Fourier transform infrared (FTIR) spectroscopy showed the presence of B and S in the obtained diamonds. The electrical properties of large diamond crystals were tested by Van der Pauw method with a four-point probe. The highest value of the hall mobility was 628.726 cm 2 /vs. And the lowest value of the resistivity was 9.33 × 10 5 Ω·cm with boron additive of 0.8 wt.% and sulfur of 2 wt.% doping to diamond which was confirmed as n -type. This work indicated that B-S co-doping to synthesize diamond crystals was a trend to promote the electrical properties of large diamond crystals.

Absract Bismuth copper oxychalcogenides, BiCuChO (Ch = S, Se, Te), are facile, and rapidly synthesized by high pressure method. The Rietveld refinement of powder X-ray diffractions shows that BiCuChO compounds have a layered crystal structure with a space group of P4/nmm. All the high pressure synthesised samples show semiconductor characteristics, while BiCuTeO prepared by the conventional method displays metal conducting behavior. The conducting behavior of BiCuTeO obtained in this study originates from the low crystal defect concentrations under the effects of high pressure; evidenced by density functional theory calculations. Large Seebeck coefficient ∼600 μV/K was obtained for BiCuSO, due to its high carrier effect mass. BiCuChO exhibits extremely low thermal conductivity ( −1 K −1 ), which decreases with an increase in the Ch 2− ion radius. The maximum figure of merit reaches 0.03, 0.31 and 0.65 for BiCuSO, BiCuSeO and BiCuTeO, respectively, values which are comparable to those for samples prepared by the conventional, complex method.

N-type thermoelectric materials PbTe doped with iodine (PbTe 1−x I x , x = 0.0001, 0.0003, 0.0007 and 0.001) were synthesized by high pressure and high temperature method (HPHT). Thermoelectric properties of PbTe 1−x I x are investigated in the range of 300–600 K. The carrier concentration of PbTe prepared by HPHT is more sensitive to I content compared to that of the PbTe 1−x I x sample prepared by other methods. The resistivities and the absolute values of Seebeck coefficients for PbTe 1−x I x increase while the thermal conductivities decrease with increasing temperature. A large power factor of 39.1 μW/(cmK 2 ) at room temperature is obtained with the carrier concentration of 9.7 × 10 18 cm −3 , which is much higher than that of Sb and Bi doped PbTe with the same synthesizing conditions. The high power factor is attributed to the high Hall mobility and large effective mass. The maximum figure-of-merit, ∼0.71 @ 600 K, is obtained for the samples with the carrier concentration of 9.7 × 10 18 cm −3 .

Type IIa large diamond crystals were synthesized in FeNiCo-C system with Ti (Cu) as nitrogen getter by temperature gradient method (TGM) under high pressure and high temperature (HPHT) conditions. Diamonds grew upon (111) facet under 5.4 GPa and 1620 K while black powder appeared around the growing diamond crystal. And the black powder covered the growing crystals in cap shape and restrained the diamond growth drastically with growth time prolonged. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the black powder described above and the regrown graphite obtained from the growth process of traditional type Ib diamonds. The black powder was proved to be micro-crystal graphite powder and the powder was similar to the regrown graphite. However, there were obvious differences between the micro-crystal graphite powder and the regrown graphite. The present discussion about precipitation mechanisms of micro-crystal graphite powder implied that the added Ti (Cu) and related reaction-products in FeNiCo-C system could change solvent property of the catalyst, which affected solubility curve of graphite. Furthermore, the practice of diamond growth indicated that the relatively high temperature and relatively low pressure conditions were remarkably responsible for the precipitation of micro-crystal graphite powder.

Polycrystalline BiCuSeO oxides are prepared by solid-state reaction followed by pressureless sintering (PLS) and high pressure sintering (HPS) methods. Both the experimental results and the density functional theory calculations indicate that the crystal defect concentrations of BiCuSeO can be reduced under the effect of high pressure. By comparing with the PLS sample, a larger power factor and a lower thermal conductivity can be obtained for the HPS sample. The maximum figure of merit ZT∼0.4 @ 800 K was obtained for the HPS sample, which is about 3 times higher than the PLS sample. These results indicate that the effect of high pressure is beneficial to modifying the microstructure and improving the thermoelectric performance of BiCuSeO oxyselenide.

In this paper, hydrothermal approach combined with high pressure sintering method was employed to synthesize PbS. The X-ray diffraction results show that single phase PbS can be obtained by a simple hydrothermal method. The scanning electron microscope results show that the PbS sample has nearly cubic shape and preserves well crystallized and coarse grains after high pressure sintering. The thermoelectric performance of PbS obtained in this study is comparable to that of a PbS sample prepared by conventional method. The carrier type and concentration of PbS can be tuned effectively by doping with Bi. The maximum figure of merit for PbS doped with 1 mol% Bi reaches 0.44 at 550 K, which is about 30 % higher than that of undoped PbS. These results indicate that hydrothermal method provides a viable and controllable way of tuning the electrical transport and thermoelectric properties for PbS.

As a well-known n-type perovskite thermoelectric oxides, SrTiO3 has always captured attention to find strategies for achieving high thermoelectric performance. In this paper, a series of reduced Sr0.9La0.1TiO3/TiO2 biphase composite ceramics were prepared via the solid-state reaction method. The effects of TiO2 on the microstructure and thermoelectric properties of the ceramics were investigated. The addition of TiO2 enhanced the carrier mobility via the formation of A-site cation vacancies and increased the carrier concentration probably through introducing oxygen vacancies in rutile TiO2 during the reduction process. Moreover, the additional phonon scattering provided by the interface between the second phase and matrix and oxygen vacancies decreased the thermal conductivity. When the TiO2 addition ratio was optimized to 25 wt%, a large power factor of 1.66 mW/K2/m and the ZT value of 0.24 were achieved at 447 K. The present strategy in this work may be feasible to broaden the range of operating temperature of SrTiO3-based oxide thermoelectric materials.

Sn–Se based layer crystals, including both SnSe and SnSe2, are promising thermoelectric materials with intrinsic ultra-low thermal conductivity due to strong anharmonicity of phonon spectrum and special bonding circumstances. In contrast to the rigid growth condition, high cost, and poor mechanical property of single crystals, Sn–Se based polycrystalline samples prepared by spark plasma sintering (SPS) or hot-pressing are more friendly for industrial scale-up. Also, it is possible to take advantage of the anisotropic transport characteristics of the Sn–Se based compounds by introducing texture in polycrystalline samples. To investigate the influences of texture and off-stoichiometry on the thermoelectric property, Sn-rich millimeter-scale SnSe crystal sheets were used as precursor in SPS. Three types of polycrystalline samples with different composition, phase structure, and texture strength were obtained. The formation mechanism and their influences on the thermoelectric properties were studied and correlated. For comparison, Se-rich millimeter-scale SnSe2 crystals were also prepared and sintered by SPS to achieve polycrystalline samples. The phase evolution, texture, thermoelectric properties and its difference and similarity with SnSe were also analyzed.

Thermoelectric materials PbTe–PbSe solid solutions (with composition of PbTe 1−x Se x (x = 0, 0.1, 0.25, 0.5) were synthesized by high pressure method successfully. The power factors of the PbTe 1−x Se x (x = 0, 0.1, 0.25) samples were nearly independent with the composition. The thermal conductivity of PbTe was depressed largely by alloying with Se. An enhanced figure-of-merit ZT ∼0.55 was obtained for x = 0.25 at room temperature. Especially, we found that PbTe 1−x Se x materials exhibited weakly temperature-dependent figure-of-merit values in the range of 300–600 K.

Using the particle swarm optimization algorithm combined with first-principles methods, we explore the diagram of AlY alloy up to 250 GPa. It is found that AlDy phase, rather than the experimentally observed B2 phase, is the most stable structure at 0 K and 0–20 GPa. However, our results show that B2 phase can exist as a stable phase at 20–27.6 GPa. At higher pressure, four new high-pressure phases with Cmcm -I, Cmcm -II, I4/mmm and P4/nmm structure are identified for the first time. The hardness, elastic and thermodynamic properties of the newly found phases are investigated and compared with B2 phase. The calculated hardness of AlDy, Cmcm -I, Cmcm -II, I4/mmm and P4/nmm phases is in the range of 7–9 GPa, higher than that of B2 phase. In addition, it is found that AlDy phase is a brittle material at 0 GPa, which changes to a ductile material above 12 GPa. Except for AlDy phase, all the other AlY compounds exhibit completely ductile behavior under pressure. Compared with the other phases, B2 phase is found to have the best ductility and the largest elastic anisotropy over the whole pressure investigated. Moreover, all AlY intermetallics exhibit a nearly elastic isotropy in compressibility but a comparatively large elastic anisotropy in shear. The structural stability, electronic structure, bulk and shear modulus, Debye temperature as well as sound velocities of AlY alloy under pressure are also deeply discussed.

In this paper, large diamond crystals were successfully synthesized under 5.6 GPa at temperature 1513 and 1553 K with melamine (C3H6N6) additive. Fourier transform infrared spectroscopy (FTIR) indicated C3H6N6 is an ideal nitrogen source for large diamond crystal synthesized by temperature gradient method (TGM), but its hydrogen is not absorbed by diamond. With the increase of C3H6N6 content, the colour of diamond changed from yellow to green, and the highest nitrogen content of diamond is 2300 ppm. High synthesis temperature can effectively reduce the formation of defects and play a key role in the formation of C-centers during diamond growth. Surprisingly, diamond is likely to grow into twin crystal when the C3H6N6 content is 0.1 wt%. In the process of diamond growth, carbon atoms of C3H6N6 are likely to serve as carbon source to form plane dislocations, which eventually lead to the formation of twin diamond. Raman spectra show that there are few crystal defects in diamond synthesized with C3H6N6 as dopant.

Diamond has a series of extreme characteristics superior to other materials, and also very wide application scope. The large diamond single crystal can play a role in its functional characteristics, which has become a research hotspot. In this paper, we introduce the principle and process of synthesizing large diamond single crystal by temperature gradient method (TGM) under high pressure and high temperature (HPHT), and summarizes the research status and research directions of different types of and additives-doped large diamond single crystals respectively. The principle of the temperature gradient method is that the carbon source, driven by the temperature gradient, diffuses from the high concentration region at the high temperature end to the low concentration region at the low temperature end, and diamonds are grown on the seed crystal. The growth rate of diamond crystal is controlled by adjusting the axial temperature gradient at synthesis cell, and the shape growth of Ib-type large diamond is controlled by the distribution in the V-shaped growth area. We introduce different kinds of diamond large single crystals from five aspects. Firstly, the Ia-type diamond large single crystal can be obtained by the annealing treatment of Ib-type diamond under HPHT. The conversion rate of C centre to A centre for nitrogen in diamond is improved by optimizing the conditions of HPHT. Secondly, the Ib-type larger diamond is studied very much in the following areas: the analysis of its surface characteristic, the control of inclusions and cracks, the precipitation mechanism and the elimination measures of regrown graphite and the mass production technology of multiseed method. Thirdly, IIa-type large diamond single crystal is introduced in which the nitrogen getter is selected due to the ability Al and Ti (Cu) to getter nitrogen, the catalyst is selected because of its effect on the nitrogen content in the diamond synthesized with Fe or Ni based catalyst, and the elimination method of microcrystalline graphite precipitation is presented by analyzing its mechanism. Fourthly, the boron elements exist in IIb-type diamond and have influence on the growth characteristics of synthetic diamond. Fifthly, introduced is the research status of diamond synthesized with B, N, S, P doping elements, in which its individual substance or their compound is used as a doping source or boron and other elements with small radius are used as co-doping agent. Then S or P with B co-doping is more conducive to the improvement of the performance of n-type diamond large single crystal semiconductor. Therefore, it is proposed that the large diamond single crystal need strengthening in mass production of IIa-type large diamond single crystal, superconducting characteristics of IIb-type large diamond single crystal, and doping of n-type semiconductors.

High-quality type IIa large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi–C system at temperature ranging from 1230 °C to 1380 °C and at pressure 5.3–5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the FeNi–C system to investigate the best ratio for high-quality type IIa diamond. Then, the different content of nitrogen getter Ti/Cu (Ti : Cu = 4 : 3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared (FTIR), are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter. Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25 °C higher than that of type Ib diamond. With the increase of the content of Ti/Cu (Ti : Cu = 4 : 3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm. The SEM results show that the synthesized crystals are mainly composed by (111) and (100) surfaces, including (311) surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type IIa diamond.

DyFe[Formula: see text]Mn[Formula: see text]O3(x[Formula: see text]=[Formula: see text]0, 0.025, 0.075, 0.15) polycrystalline samples were prepared using a traditional solid-state reaction route. The structural, magnetic and magnetocaloric properties of these samples were investigated. X-ray diffraction patterns showed that the samples exist as single-phase crystallines without peaks. The results of the Scanning Electron Microscopy (SEM) revealed that the average size of the polycrystalline particles decreased from 4.34 to 3.00 [Formula: see text]m as the Mn doping amount increased from 0.00 to 0.15. The magnetization versus temperature (M[Formula: see text]−[Formula: see text]T[Formula: see text]) plots showed that the order temperature of dysprosium (Dy) ions gradually decreased and the Morin-like transition temperature moved to the high-temperature region as x increased. The T[Formula: see text] gradually decreased from 13 to 10 K and the isotropic interaction of Fe[Formula: see text]-Fe[Formula: see text] was weakened as x increased from 0.00 to 0.15. The polycrystalline samples appeared as pre-formed clusters. The magnetization (M[Formula: see text]−[Formula: see text]H[Formula: see text]) plots revealed that all the samples underwent a first-order magnetic phase transition. The maximum magnetic entropy change, occurring near the Curie temperature, obtained at a magnetic-field span of 7 T, was 18.2 J/kg K. The maximum cooling capacity of the polycrystalline DyFe[Formula: see text]Mn[Formula: see text]O3(x[Formula: see text]=[Formula: see text]0, 0.025, 0.075, 0.15) samples was 441 J/kg.

Nanostructured thermoelectric materials PbSe co-doped with Ag and Sb (with the composition of (AgSb)xPb1−2xSe) were prepared by high pressure method. It was found that appropriate doping with Ag and Sb could reduce both the electrical resistivity and the phonon thermal conductivity simultaneously, consequently greatly enhancing the thermoelectric performance. An enhanced figure-of-merit of 1.03 has been achieved at 600 K for the sample with x = 0.03, which is about five times higher than that of undoped PbSe. The improved thermoelectric performance in this study may be due to the effect of high pressure and the low phonon thermal conductivity resulting from Ag and Sb as source of dopants.

Highly dispersed olive-like NiS particles were synthesized in a liquid-liquid biphasic system at room temperature, where nickel xanthate in organic solvents (toluene and benzene) and sodium sulfide in water solution were used as nickel and sulfide sources, respectively. NiS particles were formed at the stabilized phase interface. The structures, chemical composition and optical characteristics of the products were investigated by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The organic solvents obviously influenced the morphology of the NiS particles. The olive-like NiS with smooth surface and sharp ends was obtained at benzene/water interface, while spindle-like NiS particles with rough surface and circle ends were formed when using toluene as a solvent. Analogously, chainlike Bi2S3 nanowires were produced at chloroform/water interface. The effect of the experiment parameters including reaction time, solvent and concentration of reactants on the size and morphology of the products was discussed in detail and a possible formation mechanism was suggested.

Thermoelectric ceramics, Ag x Y y Ca2.8Co4O9 + δ (0 ≤ x, y ≤ 0.15), have been prepared using a sol-gel method, followed by pressureless sintering. The phase structures and microstructures of oxides were investigated at room temperature. Thermoelectric properties including Seebeck coefficient, electrical conductivity and thermal conductivity were measured from 303 to 973 K. It was found that the samples contain nanostructured Ag phase with grain size of 100 nm. The Ag0.05Y0.15Ca2.8Co4O9 + δ sample has the maximum figure of merit (ZT ~ 0.14 @ 973 K), which is about 27% higher than that of Ca3Co4O9 + δ .

Thermoelectric materials PbSe were successfully prepared by high pressure and high temperature technique (HPHT) and the pressure-dependent thermoelectric properties were studied from 300 to 600 K. The measurement results indicate that the electrical conduction type in PbSe can be changed from p- ( 2.0 GPa) by application of pressure of about 2.0 GPa. And the electrical resistivity can be reduced effectively by pressure. Low thermal conductivity (~0.8 W/mK) is obtained for high pressure synthesized PbSe. These results indicate that high pressure provides a viable and controllable way of tuning the thermoelectric properties for PbSe.

Herein, an ultrahigh pressure (UHP, under 5 GPa) technique was introduced to improve hydrogen storage properties of 85 mass% Mg–10 mass% Ni–5 mass% La (noted as 85 Mg–10Ni–5La) alloy by modifying the microstructures. The phase composition, phase morphologies and hydrogen storage properties of the as-cast and UHP alloys were comparatively studied. Of particular interest is that UHP treatment effectively reduces the dehydriding onset temperature, as well as improves the hydrogen sorption kinetics, with the evidence that the amount of hydrogen desorption in the UHP alloy hydride is 3.51 wt.% at 573 K, which corresponds to 60.8% of the saturated capacity, while the values in the as-cast alloy change to 2.34 wt.% and 39.5%, respectively. The reversible hydrogen storage capacities and plateau hydrogen pressure of the as-cast and UHP alloys are close. X-ray diffractions and scanning electron microscopy results indicate the similar thermodynamic property of the two alloys is associated with the same hydrogen storage phases (Mg and Mg2Ni). The improvement in the hydriding/dehydriding kinetics is ascribed to a better catalytic effect of Mg2NiH4 and a higher volume fraction of phase boundary which acts as hydrogen diffusion channel, which is related with the formation of Mg6Ni phase after ultrahigh pressure treatment. The results demonstrate that the UHP treatment is an effective pathway to tune the hydrogen storage performances of those magnesium–nickel-rare earth alloys.

Phase compositions, morphologies and hydrogen storage properties of the as-cast and copper-mould-cast LaMg4Ni alloys were studied. The dehydriding onset temperature of the as-cast alloy hydride was about 500 K, which was at least 50 K higher than that of the copper-mould-cast one, and the copper-mould-cast alloy hydride had a faster dehydriding rate compared with as-cast one. Additionally, the copper-mould-cast alloy could uptake 2.85 wt.% hydrogen, which was 95.0% of saturated hydrogen storage capacity at room temperature. While only 1.80 wt.% hydrogen (60% of saturated capacity) was absorbed for the as-cast alloy under the same conditions. The reversible hydrogen storage capacities and plateau hydrogen pressures of the two alloys were close. X-ray diffractions and scanning electron microscopy results indicated that similar thermodynamic property of the two alloys should be ascribed to the same hydrogen storage phase, Mg and Mg2Ni. The better hydrogen sorption kinetics of copper-mould-cast alloy should be ascribed to the more uniform phase distribution compared with that of the as-cast one.