In this study, {111}-oriented diamond crystals with different nitrogen concentrations were successfully synthesized in a series of experiments at 5.8 GPa pressure and 1380–1400 °C temperature.

Cu3SbS4-based materials composed of nontoxic, low-cost, and earth-abundant elements potentially exhibit favorable thermoelectric performance. However, some key transport parameters and thermal stability have not been reported. In this work, the effects of Bi and Sn co-doping on thermoelectric properties and the thermal stability of Cu3SbS4 were studied by experiment and theoretical validation. Bi and Sn doping can effectively tune the electrical properties and the electronic band structure. The Bi and Sn doping leads to an increased carrier concentration from 6.4 × 1017 to 7.4 × 1020 cm–3 and a decreased optical band gap from 0.85 to 0.73 eV. The effective mass was increased from ∼3.0 me for Bi-doped samples to ∼4.0 me for Bi and Sn co-doped samples. An enhanced power factor of 1398 μW m–1 K–2 at 623 K was obtained for Cu3Sb1–x–y Bi x Sn y S4 (x = 0.06, y = 0.09). The measurements of elastic properties exhibited a large Grüneisen parameter (γ ∼2) for Cu3SbS4-based materials. Finally, a maximum zT of 0.76 ± 0.02 at 623 K was achieved for Cu3Sb1–x–y Bi x Sn y S4 (x = 0.06, y = 0.05) sample. In addition, Cu3SbS4 materials possess excellent thermal stability after thermal treatment in vacuum at 573 K for totally 500 h and dozens of heating–cooling thermal cycles (300–623–300 K). It indicates that Cu3SbS4 is a robust alternative for Te-free thermoelectric materials at an intermediate temperature range. This work provides feasible guidance to survey the thermal stability of chalcogenides.

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In this study, type Ib diamond annealing experiments were successfully performed under a pressure of 2.5 GPa and a high temperature range between 1680 and 2060 °C. The color of the diamond changed from yellow to light yellow, and the nitrogen (N) state changed from the isolate C-center to the aggregated A-center as the annealing temperature increased. The NV0 center was detected when the annealing temperature was under 1840 °C, and not detected when the temperature reached 1920 °C. The NV– center was more stable than the NV0 center at an annealing temperature of 1920 °C. When the annealing temperature reached 1990 °C, the NE8 center appeared in the diamond lattice. When the annealing pressure changed from 2.5 to 5 GPa, high pressure would restrict the formation of A-center N but hardly affected the formation of NV− center  in the diamond lattice. This was the first known report on the successful preparation of the type IaA diamond under a lower pressure of 2.5 GPa. Our experiment results could be helpful for further understanding the formation of various centers in the diamond lattice and provided data for distinguishing the annealed synthesized diamond from the natural diamond in the jewelry market.

In this paper, we report the influence of oxygen and hydrogen additives in the metal melt on the growth process, morphology, and defect-and-impurity structure of large single-crystal diamonds.

In this paper, IIa, Ib, N-doped and N–H co-doped diamonds were studied, and the interaction mechanisms between hydrogen and nitrogen in the diamonds were investigated in detail.

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Advances in understanding the state and transformation of impurity-related defects in natural diamond have been achieved by means of high-pressure and high-temperature annealing experiments. However, the existing literature featuring complex behaviors of aggregated nitrogen and hydrogen-related defect (3107 cm −1 center) has remained controversial. Their formation mechanism during diamond crystallization is still unclear, thus further investigation is required. In this work, we have successfully synthesized a variety of high-quality diamonds containing nitrogen impurities with IaA (nitrogen pairs), IaB (group of four nitrogen atoms around a vacancy) and Ib (single-substitutional nitrogen) characteristics ranging from <1 ppm to 3380 ppm at pressures ranging from 5.0 GPa to 6.3 GPa and temperatures of 1300-1650 °C. Our results provide new experimental evidence for the aggregation of nitrogen impurities (A-and B-centers) during diamond growth. We notice that the hydrogen is easily trapped by nitrogen atoms to form nitrogen-hydrogen complexes (-NH, -NH 2 , -NH 3 ) when the nitrogen tends to form C-centers in hydrogen-enriched environments. Additionally, we observed that the high reaction temperature and formation of A-centers during diamond growth play important roles in the formation of the 3107 cm −1 center. We believe the current results could be helpful for further understanding and constructing a clear model of impurity-related defects, and thus provide us deeper insights into the genesis of natural diamond.