Critical Point Pressure Research Articles

A Quenched Disorder in the Quantum-Critical Superconductor CeCoIn5.

Emergent inhomogeneous electronic phases in metallic quantum systems are crucial for understanding high-Tc superconductivity and other novel quantum states. In particular, spin droplets introduced by nonmagnetic dopants in quantum-critical superconductors (QCSs) can lead to a novel magnetic state in superconducting phases. However, the role of disorders caused by nonmagnetic dopants in quantum-critical regimes and their precise relation with superconductivity remain unclear. Here, the systematic evolution of a strong correlation between superconductive intertwined electronic phases and antiferromagnetism in Cd-doped CeCoIn5 is presented by measuring current-voltage characteristics under an external pressure. In the low-pressure coexisting regime where antiferromagnetic (AFM) and superconducting (SC) orders coexist, the critical current (Ic ) is gradually suppressed by the increasing magnetic field, as in conventional type-II superconductors. At pressures higher than the critical pressure where the AFM order disappears, Ic remarkably shows a sudden spike near the irreversible magnetic field. In addition, at high pressures far from the critical pressure point, the peak effect is not suppressed, but remains robust over the whole superconducting region. These results indicate that magnetic islands are protected around dopant sites despite being suppressed by the increasingly correlated effects under pressure, providing a new perspective on the role of quenched disorders in QCSs.

New Method of NPOH Equation-Based to Estimate the Physicochemical Properties of Noncyclic Alkanes.

Changes in various physicochemical properties (P (n)) of noncyclic alkanes can be roughly classified as linear and nonlinear changes. In our previous study, the NPOH equation was proposed to express nonlinear changes in the properties of organic homologues. Until now, there has been no general equation to express nonlinear changes in the properties of noncyclic alkanes involving linear and branched alkane isomers. This work, on the basis of NPOH equation, proposes a general equation to express nonlinear changes in the physicochemical properties of noncyclic alkanes, including a total of 12 properties, boiling point, critical temperature, critical pressure, acentric factor, heat capacity, liquid viscosity, and flash point, named as the "NPNA equation", as follows: ln(P (n)) = a + b(n - 1) + c(S CNE) + d (ΔAOEI) + f(ΔAIMPI), where a, b, c, and f are coefficients, and P (n) represents the property of the alkane with n carbon atom number. n, S CNE, ΔAOEI, and ΔAIMPI are number of carbon atoms, sum of carbon number effects, average odd-even index difference, and average inner molecular polarizability index difference, respectively. The obtained results show that various nonlinear changes in the properties of noncyclic alkanes can be expressed by the NPNA equation. Nonlinear and linear change properties of noncyclic alkanes can be correlated with four parameters, n, S CNE, ΔAOEI, and ΔAIMPI. The NPNA equation has the advantages of uniform expression, usage of fewer parameters, and high estimation accuracy. Furthermore, using the above four parameters, a quantitative correlation equation can be established between any two properties of noncyclic alkanes. Employing the obtained equations as model equations, the property data of noncyclic alkanes, involving 142 critical temperatures, 142 critical pressures, 115 acentric factors, 116 flash points, 174 heat capacities, 142 critical volumes, and 155 gas enthalpies of formation, a total of 986 values, were predicted, which have not be experimentally measured. NPNA equation not only can provide a simple and convenient estimation or prediction method for the properties of noncyclic alkanes but also can provide new perspectives for studying quantitative structure-property relationships of branched organic compounds.

Theoretical Estimation of Disinfectant Mass Balance Components in Drinking Water Distribution Systems

The water quality audit concept is an important feature in assessing the loss of disinfectant mass in drinking water distribution systems. Based on this concept, the loss can be divided into the loss of disinfectant mass through water losses (Ml) and the decay of disinfectant mass due to chemical reactions (Mr). When an audit focuses on the effect of water losses on the loss of disinfectant mass, the decay of disinfectant mass by chemical reactions with the ideal condition of no water losses (Mro) has to be estimated; thus, the disinfectant mass associated with water losses (MWL=Ml+Mr−Mro) can be assessed. Generally, the computation of these components (Ml, Mr, and MWL) needs hydraulic and water quality modeling. In this study, we propose a novel method based on a simple theoretical analysis to evaluate these components using only two parameters: the ratio of water losses (p) and the ratio of disinfectant concentrations at the critical pressure point and the network inlet (Cp*). The coefficients of our theoretical Ml, Mr, and MWL were estimated using 20 real network models, with p between 2.8% and 54.9% and Cp* between 18.4% and 91.9%. The results showed that our equations were effective at assessing the loss of disinfectant mass in drinking water distribution networks for the top-down auditing approach.

Influence of sub-supercritical CO2 on pore structure and fractal characteristics of anthracite: An experimental study

The geological storage of CO2 in coal seams has become one of the most effective means to alleviate the greenhouse effect, and the choice of CO2 injection and storage pressure is very critical. In this study, the effects of sub-supercritical CO2 intrusion on coal pore structures were investigated by nuclear magnetic resonance (NMR) and low-pressure N2 adsorption method (LP-N2GA), and the causes were analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy. The results showed that total porosity increased by 1.25%, 4.53%, and 5.82%, respectively, and micro-minipore volume increased by 10.1%, 42.2%, and 42.7%, respectively, after anthracite was treated with 4, 8, and 12 MPa CO2. The reasons for the change of coal pore structure caused by CO2 intrusion mainly include mineral dissolution, extraction of functional groups, destruction of aromatic layers in the microcrystalline structure, and rearrangement of macromolecular structure. Additionally, supercritical CO2 possesses more of these capabilities than subcritical CO2, resulting in greater changes in coal pore structure. These findings guide us that the injection pressure of CO2 should be increased as much as possible within the scope of cost and technology and the storage pressure of CO2 near the critical pressure point should be selected.

Destabilization of binary mixing layer in supercritical conditions

Compressible mixing layer instabilities are of importance to a wide range of environmental and industrial applications. Past studies have focused on either ideal-gas or real-fluid thermodynamic regimes of single-species mixing layers. However, mixing layers of binary mixtures at supercritical conditions, commonly encountered in fuel injection systems, introduce additional complexities due to the added compositional degree-of-freedom. Moreover, the effect of strong variations in thermodynamic response functions across the Widom line on the binary mixing layer stability remains poorly understood. Thus, the objective of this study is to examine the coupling between the hydrodynamic instability and the real-fluid thermodynamics across the Widom line and its effects on the overall binary mixing layer dynamics. To this end, we develop a linear stability analysis of the full binary-species compressible transport equations coupled with the PC-SAFT equation of state. Analysis shows the existence of a novel instability mechanism that arises from juxtapositioning of the Widom-line transition and the hydrodynamic inflection point. This novel thermodynamically induced instability mechanism has the net effect of destabilizing the binary mixing layer at lowering supercritical conditions towards the critical pressure point. This is in contrast to previous stability analyses of supercritical single-species mixing layers, where increasing pressure destabilizes the flow due to its effect on reducing the density stratification. The discovered thermodynamically induced instability mechanism of binary mixing flows highlights the need for an extension of classical instability criteria to incorporate the effect of strong variations in the thermodynamic response functions across the Widom line on mixing layer instability.

Empirical Study on Human Movement Classification Using Insole Footwear Sensor System and Machine Learning.

This paper presents a plantar pressure sensor system (P2S2) integrated in the insoles of shoes to detect thirteen commonly used human movements including walking, stooping left and right, pulling a cart backward, squatting, descending, ascending stairs, running, and falling (front, back, right, left). Six force sensitive resistors (FSR) sensors were positioned on critical pressure points on the insoles to capture the electrical signature of pressure change in the various movements. A total of 34 adult participants were tested with the P2S2. The pressure data were collected and processed using a Principal Component Analysis (PCA) for input to the multiple machine learning (ML) algorithms, including k-NN, neural network and Support-Vector Machine (SVM) algorithms. The ML models were trained using four-fold cross-validation. Each fold kept subject data independent from other folds. The model proved effective with an accuracy of 86%, showing a promising result in predicting human movements using the P2S2 integrated in shoes.

A Novel Design of Rack Mount Server Thermal Simulator: Design, Assembly, and Experimental Verification

Abstract The practice of commissioning data centers (DCs) is necessary to confirm the compliance of the cooling system to the information technology equipment (ITE) load (design capacity). In a typical DC, there are different types of ITE, each having its physical characteristics. Considering these geometrical and internal differences among ITE, it is infeasible to use the actual ITE as a self-simulator. Hence, a separate device called load bank is employed for that purpose. Load banks create a dummy thermal load to analyze, test, and stress the cooling infrastructure. Available commercial load banks do not accurately replicate a server's airflow patterns and transient heat signatures which are governed by thermal inertia, energy dissipation, flow resistance, and fan system behavior. In this study, a novel prototype of the server called server simulator was designed and built with different components to be used as a server mockup. The server simulator accurately captured air resistance, heat dissipation, and the functionality of actual server behavior. Experimental data showed up to 93% improvement in ITE passive and active flow curves using the designed server simulator compared to the commercial load bank. Furthermore, the experimental results demonstrated a below 5% discrepancy on the critical back pressure and free delivery point between the actual ITE and the designed server simulator. In addition, experimental data indicated that the developed server simulator improved the actual ITE thermal mass by 27% compared to the commercial load bank.

Study on the effect of multiple non-breathable gangue occurrence on gas migration in coal seams

Abstract As the mining environment gradually moves toward deep, the form and occurrence mode of gangue are more complex. The occurrence of non-breathable gangue seriously worsens gas migration conditions, which greatly reduces the gas extraction efficiency and increases the possibility of coal and gas outburst. Therefore, in order to explore the effect of multiple non-breathable gangue occurrence on gas migration in coal seams, the self-developed the constant pressure coal and rock mass gas seepage test system is used to systematically study the characteristics of coal seam gas migration under different layers of gangue and the differentiated occurrence of multiple gangue. The equivalent characterization of coal seam gas migration under the condition of multiple inclusions is proposed through theoretical analysis and numerical simulation. Research shows: the permeability factor of the whole coal sample, sample containing a single layer gangue and sample containing double layers gangue exhibits a “V-shaped variation law with the increase of the gas adsorption equilibrium pressure. There is a critical gas pressure point when the permeability factor is the lowest, and with the increase in the number of gangue layers, the greater the pressure value of the critical gas pressure point. According to the characteristics of gas pressure distribution, the sample containing gangue can be roughly divided into four influence areas: gas expansion affected area, gas stable seepage area and upper and lower effective seepage area. The more the number of gangue layers and the larger the area of gangue layers, the upper and lower effective seepage area is smaller, the closer the positions of gangue are to the gas source, gas expansion affected area is smaller, both of them will cause more difficult in gas migration and the lower of the sample permeability factor. When different sizes of gangue are used at two positions of the gangue in the samples, with the increase of gas adsorption equilibrium pressure, the attenuation rate of permeability factor in the early stage of the sample is significantly higher than that of the sample with the same size of gangues in the front and at the back. The results of the paper have certain actual guiding significance for improving gas extraction efficiency and preventing mine gas disasters.

Analysis of the main factors affecting mass production in the plastic molding process by using the finite element method

Plastic injection molding is widely used in many industrial applications. Plastic products are mostly used as disposable parts or as portable parts for fast replacements in many devices and machines. However, mass production is always adopted as an ideal method to cover the huge demands and customers’ needs. The problems of warpage due to thermal stresses, non-uniform pressure distribution around cavities, shrinkage, sticking and overall products quality are some of the important challenges. The main objective of this work is to analyze the stress distribution around the cavities during the molding and demolding to avoid their effects on the product quality. Moreover, diagnosing the critical pressure points around and overall the cavity projection area, which is subjected to high pressure will help to determine the optimum pressure distribution and ensure filling all cavities at the same time, which is another significant objective. Computer-aided design (CAD) and CATIA V5R20 are adopted for design and modeling procedures. The computer-aided engineering (CAE) commercial software ABAQUS 6141 has been dedicated as finite element simulation packages for the analysis of this process. Simulation results show that stress distribution over the cavities depends on both pressure and temperature gradient over the contact surfaces and can be considered as the main affecting factor. The acceptable ranges of the cavity stresses were determined according to the following values: the cavity and core region temperature of 55–65 °C, filling time of 10–20 s, ejection pressure 0.85 % of injection pressure, and holding time of 10–15 s. Also, theoretical results reveal that the uniform pressure and temperature distribution can be controlled by adjusting the cavities layout, runner, and gate size. Moreover, the simulation process shows that it is possible to facilitate and identify many difficulties during the process and modify the prototype to evaluate the overall manufacturability before further investing in tooling. Furthermore, it is also concluded that tooling iterations will be minimized according to the design of the selected process

The nine development bands: A conceptual framework and global theory for waste and development.

Solid waste management (SWM) is an essential utility service. More than two to three billion people worldwide still lack basic services, whereas some countries are already moving beyond SWM towards waste and resource management (WaRM) and a circular economy. This paper sets out a novel conceptual framework and global theory of waste and development, providing a road map, allowing a country or city to locate their current position and plot their way ahead. We identify nine development bands (9DBs) with significant commonalities in terms of critical challenges and developmental pressure points. DB1–DB4 reflect stepwise improvement towards the new baseline of meeting the SDG 11.6.1 indicators of universal collection and management in controlled facilities (DB5). Countries can then choose to move towards environmentally sound management and the ‘reduce, reuse, recycle’ (3Rs) (DB6-9), with an ultimate aspiration of ‘zero waste’. We test the 9DBs conceptual framework against historical journeys of higher income countries. The main application will be in low- and middle-income countries striving towards SDG 11.6.1, where it fills a key gap in the practitioners’ toolkit by enabling initial framing/scoping of the problem and smarter interventions to be designed and sense checked. Key insights include targeted governance/institutional reforms, appropriate and affordable systems/technology and adapting solutions to a diversity of local needs and realities.

Structural and Transport Properties of 1T-VSe2 Single Crystal Under High Pressures

Two-dimensional transition metal dichalcogenide 1T-VSe2 exhibits a unique three-dimensional charge density wave (CDW) order below ∼110 K at ambient pressure, which shows unusual evolution under pressure. Here we report on the high-pressure structural and transport properties of 1T-VSe2 by extending the pressure up to 57.8 GPa, through electrical transport, synchrotron X-ray diffraction (XRD) and Raman scattering measurements, which unravel two critical pressure points. The CDW transition is found to be enhanced under compression at a rate of 16.5 K/GPa up to the first critical pressure PC1 ∼ 12 GPa, at which a structural phase transition from hexagonal P-3m1 to monoclinic C2/m phase takes place. The second critical pressure PC2 ∼ 33 GPa corresponds to another structural transition from monoclinic C2/m to P21/m phase. These findings extend the phase diagram of pressurized 1T-VSe2 and may help to understand pressure tuning of structures in transition metal dichalcogenides.

Potential impact of CO2 injection into coal matrix in molecular terms

Coal seams are one of the targeted geological bodies for CO2 sequestration. Coal structure deformation is a significant feature of the interaction between CO2 and coal seams. The rearrangement of macromolecular structure is a recognized deformation mechanism whose process has not been quantified. We used a high-order coal macromolecular model to reveal specific processes of coal macromolecular rearrangement caused by CO2 injection through molecular dynamics. In addition, the potential impact of this injection on the sequestration and mechanical properties of CO2 in the coal matrix was investigated. The rearrangement of the coal macromolecular structure is accomplished through the mutual coupling of the pore structure and macromolecular ordering. The compression of closed pores and the expansion of open pores together cause the swelling of macromolecular volumes. The concentration of closed pores was an important indicator for the quantification of the rearrangement of macromolecular structure. The greater the content of closed pores in the coal, the higher the potential for macromolecular structure transformation after CO2 injection. Furthermore, the more disordered the direction of the coal macromolecular layer, the lower the peak strength of the coal matrix. The amount of CO2 sequestration in the coal matrix is gradually saturated near the critical pressure point. Our findings contribute to the study of CO2 sequestration in coal seams and CO2 leakage risk prediction.

Study on ether spray combustion and its products under sub- and super-critical environments

In order to explore the combustion process of fuel and its products under sub- and super-critical environments, the constant volume combustion bomb system was used. The high-pressure common rail system and single injection instrument were used to supply fuel. Images of spray and combustion processes were recorded by high speed video camera using shadow photographic method, and combustion products were measured with a gas analyzer. The experimental results show that the ether flame presents a bright spherical shape. At the critical pressure point, the spray combustion penetration is the shortest, and the overall flame area is the smallest. The combustion duration of ether increases with increasing ambient pressure, reaches the maximum at the critical pressure, and then decreases with further increasing pressure. The amount of CO emitted from the combustion of the ether continuously decreases with the increase of ambient pressure. The amount of HC changes abruptly at the critical pressure. The differences between combustion characteristics and products formation are mainly due to the differences in fuel physical parameters and its break-up and evaporation mechanisms under sub- and super-critical conditions.

Resolving the puzzle of sound propagation in liquid helium at low temperatures

Experimental data suggests that, at temperatures below 1 K, the pressure in liquid helium has a cubic dependence on density. Thus the speed of sound scales as a cubic root of pressure. Near a critical pressure point, this speed approaches zero whereby the critical pressure is negative, thus indicating a cavitation instability regime. We demonstrate that to explain this dependence, one has to view liquid helium as a mixture of three quantum Bose liquids: dilute (Gross–Pitaevskii-type) Bose–Einstein condensate, Ginzburg–Sobyanin-type fluid, and logarithmic superfluid. Therefore, the dynamics of such a mixture is described by a quantum wave equation, which contains not only the polynomial (Gross–Pitaevskii and Ginzburg–Sobyanin) nonlinearities with respect to a condensate wavefunction, but also a non-polynomial logarithmic nonlinearity. We derive an equation of state and speed of sound in our model, and show their agreement with the experiment.

Structural, vibrational and electrical properties of type-II Dirac semimetal PtSe2 under high pressure

We present a high-pressure study of type-II Dirac semimetal PtSe2 single crystals through synchrotron x-ray diffraction (XRD), electrical transport and Raman scattering measurements in diamond anvil cells with pressures up to 36.1–42.3 GPa, from which two critical pressure points associated with unusual electron–phonon coupling are unraveled. We show that both resistance and phonon linewidth of Raman modes display anomalies at the first critical pressure of Pr ~ 10 GPa, in accordance with a scenario of pressure-induced disappearance/appearance of type-II/type-I Dirac points around Pr predicted previously. The second critical pressure Pc ~ 20 GPa may correspond to a structural crossover of PtSe2 from quasi-2D lattice to 3D network, which is revealed via detailed analysis of the structural parameters extracted from XRD refinement, Raman modes shifts as well as parameters from fitting of the low-temperature resistance. Our results demonstrate great tunability of PtSe2 via strain engineering, thanks to the single p-orbital manifold derived electronic states that are susceptible to out-of-plane and in-plane distances.

Higher Education in an Era of Digital Competition: Emerging Organizational Models

Growing demand among learners for improved accessibility and convenience, lower costs, and direct application of content to work settings is radically changing the environment for higher education in the United States and globally. In this rapidly changing environment, which is increasingly based within the context of a global, knowledge-based economy, traditional universities are attempting to adapt purposes, structures, and programs, and new organizations are emerging in response. Organizational changes and new developments are being fueled by accelerating advances in digital communications and learning technologies that are sweeping the world. Growing demand for learning combined with these technical advances is in fact a critical pressure point for challenging the dominant assumptions and characteristics of existing traditionally organized universities in the 21st century. This combination of demand, costs, application of content and new technologies is opening the door to emerging competitors and new organizations that will compete directly with traditional universities and with each other for students and learners.This paper describes and analyzes seven models of higher education organization that are challenging the future preeminence of the traditional model of residential higher education. These models are emerging to meet the new conditions and to take advantage of the new environment that has created both opportunity and risk for all organizations, and which demands experimentation of structure, form, and process.Each of the seven models discussed offers an alternative to traditional residential higher education. Several models are in their infancy. Several others operate at the margin of organizations with other core businesses or priorities. At least one of the models depends upon extensive collaborations. All of the models incorporate features that are designed to enable universities to better respond to new educational demands and opportunities at a national and international level. Taken together, these organizational models are emerging as significant forces in providing education and training, and as powerful competitors to traditional universities. They offer the prospect of rapidly changing where, when, how and for what purpose education is organized within both the corporate and the higher education communities in the United States and throughout the world. The result is a dynamic competitive environment among traditional universities that are adapting learning processes and administrative procedures, alternative nontraditional universities that are adapting technologies to better serve their existing primarily adult constituencies, and new universities that are being formed around the promise of virtual environments. The thesis of this paper is that growth in worldwide demand for learning is combining with improved learning technologies to force existing universities to rethink their basic assumptions and marketing strategies. This new digital environment is further encouraging and enabling the creation of new and innovative organizational models of that are challenging traditional residential universities to change more quickly and dynamically.

Pressure-induced evolution of structural and electronic properties in TiTe2

Bulk $1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$ (hexagonal, space group P-$3m1$) exhibits semimetallic conductivity with weak Anderson localization characteristic at ambient pressure, but superconductivity under high pressure of $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. Here the detailed evolutions of structural and transport properties in $\mathrm{TiT}{\mathrm{e}}_{2}$ during compression are investigated by extending pressure up to 50.2 GPa. The combined high-pressure electrical transport and synchrotron x-ray diffraction experiments unravel two critical pressure points. At ${P}_{c1}\ensuremath{\sim}5.4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, the superconductivity emerges, which is accompanied by a structural transition from $P\text{\ensuremath{-}}3m1$ to a mixture of $P\text{\ensuremath{-}}3m1$ and monoclinic $C2/m$ phase. The localization effect maintains until the structural transition is over at ${P}_{c2}\ensuremath{\sim}19.1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, meanwhile the Hall coefficient ${R}_{\mathrm{H}}$ changes from positive to negative. Our results demonstrate that the superconductivity in the pressurized $\mathrm{TiT}{\mathrm{e}}_{2}$ can be assigned to the high-pressure $C2/m$ phase which is electron dominated.

Pressure-dependent photoluminescence of CdSe/ZnS quantum dots: Critical point of different pressure regimes

High pressure condition can alter and control the electronic structure of semiconductor quantum dots, and therefore provides novel insight for designing optoelectronic devices. Here we report the pressure-dependent photoluminescence (PL) of CdSe/ZnS core/shell quantum dots (QD) in different pressure regimes. The center of the PL spectrum has blue-shift when hydrostatic pressure increases, due to the increasing bulk modulus. However, the shifting rate becomes lower in the higher pressure regime, i.e. above the critical pressure point, mainly due to the interaction between QDs. Accordingly, the lifetimes of PL drop in the low pressure regime, due to the increased pressure-induced trapping states, then increase above the critical pressure point, indicating the interaction between dots likewise. The observed critical pressures for both cases are consistent with each other, and strongly depend on the QD concentration, which forcefully support the aforementioned interaction model.

Numerical study on the effects of opening form on the deflation for an air-supported membrane structure

Air-supported membrane structure has been widely applied to large-span space due to its advantages of light weight, low cost, reusability. The static load bearing capacity and the dynamic deployment simulation of air-supported membrane structure have received extensive attention. However, very few studies have been reported to investigate its deflation behavior. Although several dynamic finite element algorithms can be applied to the deflation simulation, their computational costs are large. The concept of critical pressure point was introduced in this paper, by which the deflation process was divided into two stages of decompression and collapse. A series of numerical simulations were performed to study the effects of opening area and position on the pressure change in decompression process for air-supported membrane structure. The study showed that the required time for the critical pressure point reached initially decreases sharply gradually evolving into a slight decrease as the opening area increases from 0.5 to 6 m2, which followed a power equation as a function of opening area. Moreover, for a fixed opening area, opening position at top exhibits a minimum value followed by middle position, while a maximum value is shown when the opening is at bottom position. It is obviously that the decompression phase is affected significantly by the opening area and position. The above results have a certain meaning for safety assessment of personal evacuation under emergency deflation of the air-supported membrane structure.

Ground-state structures, physical properties and phase diagram of carbon-rich nitride C5N

Using the ab initio evolutionary algorithm, four thermodynamically stable C5N phases (, -1, -2 and C2/m) are uncovered. The structures of the , -1 and -2 phases possess layered features. The dense C2/m phase with 3D strong covalent bond network is calculated to be superhard with hardness of 75.4 and 83.9 GPa by Chen and Gao models. The electronic properties of the C5N is diverse including conductor (), indirect semiconductor (-1 and -2) and direct semiconductor (C2/m). Pressure-induced phase transition sequences and critical pressure points are calculated to be → -1 → -2 at 2.7 and 34 GPa, respectively. Though the C2/m phase is metastable at zero temperature, our established pressure-temperature phase diagram of C5N shows that the C2/m becomes stable under high temperatures and pressures. The pressure-temperature phase diagram will give theoretical guidance for further experimental synthesis of different C5N phases.