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Determination of the structures of materials involving more light elements such as boron-rich compounds is challenging and technically important in understanding their varied compositions and super...

Mn2+:CsPbCl3 nanocrystals (NCs) were synthesized using a modified one-pot injection method, which exhibits significantly improved thermal stability. For the first time, the pressure-treated optical and structural properties of synthetic Mn2+:CsPbCl3 NCs were further investigated, and their associated intriguing electrical and photoelectric properties were revealed from impedance spectra and photocurrent measurements under compression. The pressure-dependent photoluminescence experienced an initial redshift before 1.7 GPa followed by a continuous blueshift, as evidenced by the bandgap shifts. High-pressure XRD spectra uncovered a cubic-to-orthorhombic structural transition at about 1.1 GPa and subsequent amorphization upon further compression, which was fully reversible. Furthermore, the sample annealing from 340 K drove grain growth and decreased grain boundary resistance at ambient pressure. The compression further decreased the grain boundary barrier and improved the electrical conductivity (up to ∼10−2 Ω−1 cm−1) of the thermally annealed Mn2+:CsPbCl3 NC surface. Simultaneous photocurrent enhancement of thermally annealed NCs was also achieved as expected, and reached optimal performance at 0.7 GPa. Strikingly, after the pressure cycling (loading–releasing), the results show that thermally annealed Mn2+:CsPbCl3 NCs gained preservable higher electrical conductivity (∼10 times increase) and an improved photoelectric response compared to the ambient state before compression. This work proves that high pressure is useful for opening the versatility in the structure and properties of metal–halide perovskite nanocrystals leading to a promising way for superior optoelectronic materials-by-design.

The structural phase transition of synthetic ZnFe2O4 nanoparticles (ZFO NPs) is investigated as a function of pressure up to 40.6 GPa at room temperature for the first time, and its associated intriguing electrical transport properties are resolved from in situ impedance spectra and magnetoresistivity measurements. Significant anomalies are observed in the properties of the grain boundary resistance (Rgb), the relaxation frequency (fmax), and the relative permittivity (er) in the ZFO NPs under the pressures around 17.5–21.5 GPa. These anomalies are believed to be correlated with a cubic-to-orthorhombic phase transition of ZnFe2O4 at the pressures between 21.9 and 25.7 GPa, which is found to be partially reversible. The pressure-tuned dielectric properties are measured for the cubic and the orthorhombic phases of ZFO, respectively. Remarkably, Rgb decreases up to 6 orders of magnitude as a function of pressure in the cubic phase. The dielectric polarization is obviously strengthened with increased fmax and...

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 ...

In this study, single crystal diamonds were successfully synthesized in a FeNi-S-C system under the constant conditions of 5.5 GPa and 1400 °C. The growth rate of the diamonds decreased due to the existence of sulfur (S) in the synthesis system. The color of the diamonds changed from yellow to light yellow with an increase in the S content. Compared to common type Ib diamonds synthesized in a FeNi-C system, the nitrogen concentration was higher in the synthesized diamonds when 0.1 wt% S was added but was lower when the amount of S was increased to 0.25 wt%. Raman measurements indicated that the use of S had almost no effect on the diamond lattice structure, thus diamond crystals with a high-quality sp3 structure were obtained. The photoluminescence (PL) spectra showed that the nitrogen-vacancy (NV) center occurred more likely in diamond lattice growth along the {111} face. Compared to the NV− center, the NV0 center could not be easily generated in the type Ib diamond lattice without the addition of S. Even if the NV0 and NV− centers were generated simultaneously in the diamond lattice with the addition of 0.25 wt% S, the intensity was higher for the NV− peak than for the NV0 peak. The results of this study improve our understanding of the formation mechanisms of natural diamonds and represent an effective method for controlling the NV center in the diamond lattice.

The exploration of the vast phase space of transition metal nitrides is critical for discovering novel materials and potential technological applications. Manganese mononitride with a tetragonal structure (space group I4/mmm) was synthesized in a laser-heating diamond anvil cell, which could be quenched to ambient pressure. The bulk modulus of 173 GPa was measured using in situ high-pressure diffraction, and the axial compressibility shows that, under pressure, the a direction is much more compressible than the c direction in tetragonal MnN. DFT results with correction of the on-site repulsion (GGA + U) confirm that tetragonal MnN is energetically stable and antiferromagnetic. This study highlights the need to include on-site repulsion to understand 3d metal nitrides.

In this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C10H10Fe additive, high pressures and high temperatures range of 5.2–6.2 GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C10H10Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated wi...

The synthesis of phosphorus and nitrogen co-doped diamond is investigated in the NiMnCo–C system by adding P 3 N 5 or carbonyl iron powders mixed with phosphorus powders under high pressure and high temperature. Experimental results show that the color distribution in diamond crystals with low concentration of P 3 N 5 additive is not uniform. The color becomes deep green with the increase of P 3 N 5 additive. The optical images and FTIR spectra reveal that the nitrogen atoms are more easily incorporated via {111} than {100} in the same conditions. In addition, the result of FTIR spectra of synthesized diamond indicates that the hydrogen atoms in the form of sp 3 –CH 2 – are more likely to enter the diamond lattice in the P/N co-doped system, compared with the single N-doped system. The absorption peak at 3107 cm − 1 attributed to vibration of H-related point defects (sp 2 –CH CH–) is observed in diamonds, which is often found in natural diamonds. The Raman shifting to lower frequency and FWHM value becoming wider are due to the doping of phosphorus atoms.

The temperature and convection fields of a catalyst with three different heights were simulated in a temperature gradient growth (TGG) system under high pressure and high temperature (HPHT) conditions. Temperature fields were simulated to rule out the influence of temperature on the crystal morphology. The features of the calculated convection field could predict the particular situations of diamond growth systems very well, and could explain the change of diamond morphology accompanying the growth process. According to the calculated results, we predict that the morphology of a diamond crystal changes from cubic crystal to cub-octahedral. A good agreement has been obtained between the calculated results and the observed experimental data. The morphology and structural properties of the synthesized samples are characterized by optical microscopy and a Raman spectrum. The results illustrate that the synthesized diamond crystals have less lattice distortion and with high quality.

The discovery of electrides, in particular, inorganic electrides where electrons substitute anions, has inspired striking interests in the systems that exhibit unusual electronic and catalytic properties. So far, however, the experimental studies of such systems are largely restricted to ambient conditions, unable to understand their interactions between electron localizations and geometrical modifications under external stimuli, e.g., pressure. Here, pressure-induced structural and electronic evolutions of Ca2N by in situ synchrotron X-ray diffraction and electrical resistance measurements, and density functional theory calculations with particle swarm optimization algorithms are reported. Experiments and computation are combined to reveal that under compression, Ca2N undergoes structural transforms from R 3 ¯ m symmetry to I 4 ¯ 2d phase via an intermediate Fd 3 ¯ m phase, and then to Cc phase, accompanied by the reductions of electronic dimensionality from 2D, 1D to 0D. Electrical resistance measurements support a metal-to-semiconductor transition in Ca2N because of the reorganizations of confined electrons under pressure, also validated by the calculation. The results demonstrate unexplored experimental evidence for a pressure-induced metal-to-semiconductor switching in Ca2N and offer a possible strategy for producing new electrides under moderate pressure.

The effect of the catalyst height on the morphology of diamond crystal is investigated by means of temperature gradient growth (TGG) under high pressure and high temperature (HPHT) conditions with using a Ni-based catalyst in this article. The experimental results show that the morphology of diamond changes from an octahedral shape to a cub-octahedral shape as the catalyst height rises. Moreover, the finite element method (FEM) is used to simulate the temperature field of the melted catalyst/solvent. The results show that the temperature at the location of the seed diamond continues to decrease with the increase of catalyst height, which is conducive to changing the morphology of diamond. This work provides a new way to change the diamond crystal morphology.