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Silicon carbide (SiC) is a substance found in natural diamond inclusions. Analyzing the influence of SiC doping on the properties of synthetic diamonds is vital to understanding the growth mechanism of natural diamonds and the material composition of the mantle. In this work, China-type large volume cubic high-pressure apparatus (CHPA) (SPD-6 × 1200) was used to simulate the high-temperature and high-pressure environment of diamond growth. The influence of different SiC doping contents on the crystal characteristics of a Ib-type diamond synthesized in a Fe–Ni–C system was investigated at a pressure of 5.8 GPa and a temperature range of 1650–1670 K. Optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy (PL) were used to characterize the synthesized crystals. The OM results show that the growth rate of the diamond decreases gradually, and the color changes from yellow to light yellow with an increase in the doping concentration. The FTIR results indicate that the nitrogen element in the crystal mainly appears in the diamond crystal in monatomic form (C center). The nitrogen content in the diamond gradually decreases from 275 ppm to 115 ppm with an increase in the SiC dopant ratio. The Raman data show that the FWHM (full width at half maximum) of the diamond crystal increases with an increase in the doping ratio. The XPS results demonstrate that silicon has successfully entered the diamond lattice with a Si–C bond in the crystal. The PL results indicate that the peak intensity of the nitrogen-vacancy (NV−) color center (638 nm) in the synthesized diamond crystal increases as the doping ratio increases. As the SiC doping content increases, the peak of the NV0 color center (575 nm) appears, and the peak intensity increases. [ABSTRACT FROM AUTHOR]

Studying the influence of oxygen on the growth and properties of diamond has research significance. In this paper, we created an oxygen-rich environment by adding Ni2O3 to the Fe–Ni–C system. Large single crystals of oxygen-containing diamond were successfully synthesized using the temperature gradient method (TGM) in a China-type large volume cubic high-pressure apparatus (CHPA) at 5.5–6.0 GPa and 1360–1600 °C. The results show that with the increase of the Ni2O3 content in the Fe–Ni–C system, the rate of diamond growth decreased while the conditions for diamond growth were enhanced. The morphology of the diamonds changed from {111}, {110} and {113} mixed faces to {111} dominant face. The IR results show that the presence of Ni2O3 increased the nitrogen content in diamonds from 237 ppm to 543 ppm. When 3.5 wt% Ni2O3 was added, A-centre nitrogen began to appear in the diamonds. The XPS results confirmed that oxygen successfully entered the diamond lattice in the form of C–O, C＝O, O–C＝O and N–O with a high concentration of Ni2O3 additives. Meanwhile, there were no obvious impurity inclusions and cracks in the diamond crystals. In addition, the Raman peak position of the diamond appeared to red shift, and the FWHM increased from 4.93 cm−1 to 5.52 cm−1. [ABSTRACT FROM AUTHOR]

Herein, the characteristics of heavy FeS-doped diamond crystals were studied using a China-type large volume cubic high-pressure apparatus (CHPA) with FeNi alloy as the catalyst at 6.0–6.5 GPa and 1350–1400 °C. The crystals were characterized via optical microscopy (OM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy (Raman). OM of the crystal showed that the crystals cracked when the doping ratio was increased, and an increase in pressure was beneficial to alleviate the phenomenon of cracking. The XPS spectrum of the crystal showed that S successfully enters the diamond lattice in three bonding modes, C–SO2–C6H5, C–S–SO2–C and C–S, under high concentration doping conditions. The infrared spectrum showed that the content of N in the crystal decreased with an increase in the doping ratio. The Raman spectroscopy analysis showed that the heavy FeS-doped Ib-type diamond single crystal has a high quality sp3 structure, and the full width at half maximum (FWHM) of the crystal gradually broadened as the doping ratio increased. Additionally, it showed that increasing the pressure under the same doping concentration is beneficial to increase the crystallinity of the crystal. [ABSTRACT FROM AUTHOR]

With the implementation of 14th Five-Year Plan in China and the completion of the poverty alleviation task, the economy in China has made great progress. However, the carbon dioxide (CO2) emission has also increased, which will lead to the greenhouse effect for threatening economic development and affecting people's lives. Global warming has become the greatest challenge to contemporary economic and social development, and the transition to low-carbon economy has become a general trend of world economic development. Meanwhile, the traditional neural network method for predicting the economy and CO2 emissions is not accurate and objective because of the unbalanced labeling of training data and the inability to capture the relationship between time series data. Therefore, an economy and CO2 emission prediction model based on temporal attention Gate Recurrent Unit (GRU) (TA-GRU) with loss function Balanced Mean Square Error (BMSE) (BTA-GRU) mechanism is proposed to analyze and optimize the energy structure of 27 provincial-level administrative regions in China. Due to the unbalanced data labels in the different energy structure of different regions, the improved loss function BMSE is used to solve the problem of unbalanced labels from the perspective of statistics. Then, with coal, gasoline, petroleum, coke, fuel oil, diesel, natural gas and crude oil as inputs, the per capita Gross Domestic Product (GDP) as the desired output and the CO 2 as the undesired output, the GRU can better capture time step dependencies in time series, and the attention mechanism can assign different weights to each time step, so that the proposed method can better learn data features and improve the accuracy of the an economic and CO2 emission prediction model. Finally, the CO2 emission and economic prediction model of different provincial-level administrative regions in China is established based on this proposed method. The experimental results show that compared with other mainstream time series data prediction models, this proposed model has better stability and practicability, and its mean absolute error (MAE), mean absolute percentage error (MAPE) and root mean square error (RMSE) reach 3.43, 3.28% and 2449.57, respectively. Furthermore, according to the actual situation of efficient provincial administrative regions, the energy structure of inefficient provincial administrative regions can be adjusted and optimized. Such as the energy structure of Hebei Province can be adjusted according to the energy structure of Beijing, it is estimated that the CO2 emissions of Hebei will be reduced by 82,972.43 × 10000 tons (WT) and its per capita GDP will be increased by 115,856 Yuan. Moreover, Chinese provincial governments should vigorously promote the use of clean energy, accelerate the establishment of a sound green low-carbon circular development economic system, and help achieve the goal of carbon neutrality. • The BMSE function is used to solve the problem of unbalanced data labels. • Novel economy and CO 2 emissions prediction model based on a BTA-GRU is proposed. • The proposed method can achieve state-of-the-art performance. • Energy structure of inefficient provincial administrative regions in China can be optimized. • Policy implication about clean energy for Chinese provincial governments is provided. [ABSTRACT FROM AUTHOR]

Pressure is a vital condition in the synthesis of diamond crystals via the temperature gradient method. Exploring the effect of pressure on the growth of diamond crystals is vital. In this study, we investigated the synthesis of diamond crystals using iron–nickel alloy catalysts and analyzed the properties of the synthesized diamonds in the pressure gradient using a China-type large-volume cubic high-pressure apparatus. The synthesis temperature of 1600 K and pressure range of 5.5–6.5 GPa were used. The results of Raman spectra showed that increasing the pressure would increase the crystallinity of diamond crystals. The FTIR spectra of diamond samples featured peaks at 1332 (N+ ions), 1130, and 1344 cm−1, indicating that with increasing pressure, the concentration of nitrogen atoms and ions in diamonds significantly decreased. The photoluminescence spectra of nitrogen ions in diamond samples displayed a peak at 40–100 ppm. The 692 and 694 nm peaks and the phonon bands of NV-chromophores gradually weakened with increasing pressure, indicating that the 692 and 694 nm peaks are attributable to the NV-color center and phonon displacement energy of 165 meV occurred. The Electron paramagnetic resonance spectra displayed a phonon bands of the NV-color center phonon are expressed in EPR through the g-value of NV-.These test results indicated that the pressure featured a significant effect on the nitrogen concentration and the nitrogen-related defects in diamonds. • It is proved that pressure cannot effectively improve the quality of the surface morphology of diamond crystals. • The residual stress and half-peak width by Raman spectroscopy verified that pressure can improve the crystal quality of diamond crystals. • It was demonstrated that the increase in pressure can reduce the growth rate of diamond crystals and thus the nitrogen content and related defects, and N+ ions were found in diamond crystals with lower nitrogen content. • PL spectra and EPR spectra illustrate that phonon boundaries of NV-color centers are produced at 40–100 ppm of nitrogen in diamond crystals. [ABSTRACT FROM AUTHOR]

• High-quality gem diamond were successfully synthesized in the pure Fe-C system. • There are no NV0, NV− center in diamond synthesized in pure Fe-C system. • Our findings are greatly helpful for the synthetic high-purity diamond crystal. In this paper, the diamond large single crystals were successfully synthesized in the pure Fe-C system by temperature gradient growth (TGG) method in China-type cubic anvil high-pressure apparatus (CHPA) at 5.8 GPa and 1550 °C. The synthesized diamonds were characterized by Optical microscopy, Infrared spectroscopy, Raman spectroscopy and Photoluminescence (PL) spectroscopy. The results show that the nitrogen concentration of type Ib diamonds synthesized in pure Fe-C system is about 80 ppm, which is much lower than diamonds synthesized by Ni-based and Fe-based alloys. PL spectra result indicated that there were no peaks related to the NV centers in diamonds synthesized by Fe-C system. In addition, high-quality type IIa gem diamond can be synthesized by adding a small amount of nitrogen getter in the pure Fe-C system. We believe that this work is of great significance for the synthesis of high-purity large single type IIa diamonds without impurities such as nitrogen and metals. [ABSTRACT FROM AUTHOR]