Disordered structures of boron nitride (BN), graphite, boron carbide (BC), and boron carbon nitride (BCN) systems are considered important precursor materials for synthesis of superhard phases in these systems. However, phase transformation of such materials can be achieved only at extreme pressure-temperature conditions, which is irrelevant to industrial applications. Here, the phase transition from disordered nanocrystalline hexagonal (h)BN to superhard wurtzitic (w)BN was found at room temperature under a pressure of 6.7 GPa after applying large plastic shear in a rotational diamond anvil cell (RDAC) monitored by in situ synchrotron X-ray diffraction (XRD) measurements. However, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN but probably underwent a reversible transformation to a high-pressure disordered phase with closed-packed buckled layers. The current phase-transition pressure is the lowest among all reported direct-phase transitions from hBN to wBN at room temperature. Usually, large plastic straining leads to disordering and amorphization; here, in contrast, highly disordered hBN transformed to crystalline wBN. The mechanisms of strain-induced phase transformation and the reasons for such a low transformation pressure are discussed. Our results demonstrate a potential of low pressure-room temperature synthesis of superhard materials under plastic shear from disordered or amorphous precursors. They also open a pathway of phase transformation of nanocrystalline materials and materials with disordered and amorphous structures under extensive shear.plastic deformation | transition mechanism S ynthesis of superhard materials in the boron carbon nitride (BCN) system under high pressure and temperature is one of the modern directions in high-pressure material science with significant technological potential. In particular, superhard wurtzitic boron nitride (wBN) and, especially, cubic boron nitride (cBN) are of great interest because of their unique properties: high hardness, high thermal conductivity, chemical inertia to ferrous materials, high dynamic strength, and high wear resistance, etc. (1). They can be obtained, in particular, by the direct solid-solid phase transitions initiated from the graphite-like boron nitride (BN) phases [i.e., hexagonal (h)BN and rhombohedral (r)BN] under extreme conditions. Specifically, hBN-to-wBN phase transition has been extensively studied in both dynamic and static high-pressure experiments. An important parameter that determines transformation pressure and mechanism is the concentration of the turbostratic stacking faults or degree of disordering. It was found that a highly ordered hBN transforms to wBN when compressed to high pressures [8.1-13 GPa (2-5)] at either room or high temperatures. The lowest pressure at which highly ordered hBN-to-wBN transformation starts at room temperature is, thus far, 8.1 GPa; it starts to become irreversible above 10 GPa; transformation does not complete up to 25 GPa (4, 6). In ref. 3, highly ord...

Soils are among the important sources of atmospheric nitric oxide (NO) and nitrous oxide (N O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer-reviewed publications with 520 field measurements were synthesized using meta-analysis procedure to examine the N fertilizer-induced soil NO and the combined NO+N O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO-N fluxes were estimated to be 4.06 kg ha yr , with the greatest (9.75 kg ha yr ) in vegetable croplands and the lowest (0.11 kg ha yr ) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO (EF ) and combined NO+N O (EF ) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71-1.61% and 1.81-3.35%, respectively. Forests had the greatest EF (2.39%). Within the croplands, the EF (1.71%) and EF (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EF (2.93%) and EF (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands.

As a new type of topological materials, ZrTe 5 shows many exotic properties under extreme conditions. Using resistance and ac magnetic susceptibility measurements under high pressure, while the resistance anomaly near 128 K is completely suppressed at 6.2 GPa, a fully superconducting transition emerges. The superconducting transition temperature T c increases with applied pressure, and reaches a maximum of 4.0 K at 14.6 GPa, followed by a slight drop but remaining almost constant value up to 68.5 GPa. At pressures above 21.2 GPa, a second superconducting phase with the maximum T c of about 6.0 K appears and coexists with the original one to the maximum pressure studied in this work. In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopy combined with theoretical calculations indicate the observed two-stage superconducting behavior is correlated to the structural phase transition from ambient Cmcm phase to high-pressure C2/m phase around 6 GPa, and to a mixture of two high-pressure phases of C2/m and P-1 above 20 GPa. The combination of structure, transport measurement, and theoretical calculations enable a complete understanding of the emerging exotic properties in 3D topological materials under extreme environments.high pressure | Dirac semimetals | superconductivity | synchrotron X-ray diffraction S ince the first report of topological insulator, an extensive attention in recent years has been focused on newly emergent Dirac materials including topological insulators (1-3), Dirac semimetals (4, 5), and Weyl semimetals (5-7) for their unique quantum phenomena. ZrTe 5 has been studied for a long time due to its large thermoelectric power (8, 9), resistivity anomaly (10, 11), and large positive magnetoresistance (12). Recent theoretical works (13,14) have proposed that single-layer ZrTe 5 is a large gap quantum spin hall insulator, but the bulk ZrTe 5 behaves between the strong and weak topological insulator. These predictions spark the renewed interest in the investigation of its Dirac and topological characters. Indeed, the magnetotransport experiments (15) have observed the chiral magnetic effect, both angle-resolved photoemission spectroscopy (15) and magneto-infrared spectroscopy (16, 17) study show the electronic structure of ZrTe 5 is similar with other three-dimensional (3D) Dirac semimetals like Na 3 Bi (18-20) and Cd 3 As 2 (21-25). These results suggest that ZrTe 5 is a very promising system that hosts topological properties and might help to pave a new way for further experimental studies of topological phase transitions.As one of the fundamental state parameters, high pressure is an effective, clean way to tune lattice as well as electronic states, especially in quantum states (26)(27)(28). In this work, by performing resistance and ac magnetic susceptibility measurements on ZrTe 5 single crystal at various pressures up to 68.5 GPa, a superconducting transition at 1.8 K was first noticed at a pressure of 6.2 GPa. It was interesting to notice that the occurrence of the metallic pha...

Group V elements in crystal structure isostructural to black phosphorus with unique puckered two-dimensional layers exhibit exciting physical and chemical phenomena. However, as the first element of group V, nitrogen has never been found in the black phosphorus structure. Here, we report the synthesis of the black phosphorus–structured nitrogen at 146 GPa and 2200 K. Metastable black phosphorus–structured nitrogen was retained after quenching it to room temperature under compression and characterized in situ during decompression to 48 GPa, using synchrotron x-ray diffraction and Raman spectroscopy. We show that the original molecular nitrogen is transformed into extended single-bonded structure through gauche and trans conformations. Raman spectroscopy shows that black phosphorus–structured nitrogen is strongly anisotropic and exhibits high Raman intensities in two Ag normal modes. Synthesis of black phosphorus–structured nitrogen provides a firm base for exploring new type of high-energy-density nitrogen and a new direction of two-dimensional nitrogen.