Phase Transition and Negative Thermal Expansion Property of ZrMnMo_3O_(12)

A novel material of ZrMnMo3012 with negative thermal expansion is presented. The phase transition temperature and coemcient of thermal expansion （CTE） are investigated by temperature-dependent x-ray diffraction and Raman spectra. It is shown that ZrMnMo3012 adopts monoclinic structure with space group P21/a （No. 14） from 298 to 358K and transforms to orthorhombic with space group Pnma （No. 62） above 363K. The linear CTE obtained from the results of XRD refinement is -2.80 × 10-6 K-1 from 363 to 873 K. The CTE of the bulk cylinder ceramic measured by a thermal dilatometer is -4.7× 10-6 K-1 from 373 to 773K approximatively.

Phase transition and high temperature thermoelectric properties of copper selenide Cu_(2-x) Se (0 ≤ x ≤ 0.25)

With good electrical properties and an inherently complex crystal structure, Cu2-xSe is a potential ＂phonon glass electron crystal＂ thermoelectric material that has previously not attracted much interest. In this study, Cu2-xSe （0 ≤ x ≤0.25） compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2-xSe were investigated in the temperature range of 300 K-750 K. The results of X-ray diffraction at room temperature show that Cu2-xSe compounds possess a cubic structure with a space group of Fm3m （#225） when 0.15 〈 x ≤ 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

Investigations of phase transition, elastic and thermodynamic properties of GaP by using the density functional theory

The phase transition of gallium phosphide （GAP） from zinc-blende （ZB） to a rocksalt （RS） structure is investigated by the plane-wave pseudopotential density functional theory （DFT）. Lattice constant a0, elastic constants cij, bulk modulus B0 and the pressure derivative of bulk modulus B0 are calculated. The results are in good agreement with numerous experimental and theoretical data. From the usual condition of equal enthalpies, the phase transition from the ZB to the RS structure occurs at 21.9 GPa, which is close to the experimental value of 22.0 GPa. The elastic properties of GaP with the ZB structure in a pressure range from 0 GPa to 21.9 GPa and those of the RS structure in a pressure range of pressures from 21.9 GPa to 40 GPa are obtained. According to the quasi-harmonic Debye model, in which the phononic effects are considered, the normalized volume V/Vo, the Debye temperature 8, the heat capacity Cv and the thermal expansion coefficient a are also discussed in a pressure range from 0 CPa to 40 GPa and a temperature range from 0 K to 1500 K.

Phase transition in evolution of traffic flow with scale-free property

This paper investigates the behaviour of traffic flow in traffic systems with a new model based on the NaSch model and cluster approximation of mean-field theory. The proposed model aims at constructing a mapping relationship between the microcosmic behaviour and the macroscopic property of traffic flow. Results demonstrate that scale-free phenomenon of the evolution network becomes obvious when the density value of traffic flow reaches at the critical point of phase transition from free flow to traffic congestion, and jamming is limited in this scale-free structure.

Phase transition and thermodynamic properties of TiO_2 from first-principles calculations

The pressure induced phase transitions of TiO2 from anatase to columbite structure and from rutile to columbite structure and the temperature induced phase transition from anatase to rutile structure and from columbite to rutile structure are investigated by ab initio plane-wave pseudopotential density functional theory method （DFT）, together with quasi-harmonic Debye model. It is found that the zero-temperature transition pressures from anatase to columbite and from rutile to columbite are 4.55 GPa and 19.92 GPa, respectively. The zero-pressure transition temperatures from anatase to rutile and from columbite to rutile are 950 K and 1500 K, respectively. Our results are consistent with the available experimental data and other theoretical results. Moreover, the dependence of the normalized primitive cell volume V/Vo on pressure and the dependences of thermal expansion coefficient α on temperature and pressure are also obtained successfully.

First-principles calculations for transition phase and thermodynamic properties of GaAs

The transition phase of GaAs from the zincblende （ZB） structure to the rocksalt （RS） structure is investigated by ab initio plane-wave pseudopotential density functional theory method, and the thermodynamic properties of the ZB and RS structures are obtained through the quasi-harmonic Debye model. It is found that the transition from the ZB structure to the RS structure occurs at the pressure of about 16.3 GPa, this fact is well consistent with the experimental data and other theoretical results. The dependences of the relative volume V/V0 on the pressure P, the Debye temperature Θ and specific heat Cv on the pressure P, as well as the specific heat CV on the temperature T are also obtained successfully.

Phase transition and thermodynamic properties of SrS via first-principles calculations

The phase transition of SrS from NaCl structure （B1） to CsCl structure （B2） is investigated by means of ab initio plane-wave pseudopotential density functional theory, and the thermodynamic properties of the B1 and the B2 structures are obtained through the quasi-harmonic Debye model. It is found that the transition phase from the B1 to the B2 structures occurs at 17.9 GPa, which is in good agreement with experimental data and other calculated results. Moreover, the thermodynamic properties （including specific heat capacity, the Debye temperature, thermal expansion and Griineisen parameter） have also been obtained successfully.

Phase transition and thermodynamic properties of BiFeO_3 from first-principles calculations

The first-principles projector-augmented wave method employing the quasi-harmonic Debye model,is applied to investigate the thermodynamic properties and the phase transition between the trigonal R3c structure and the orthorhombic Pnma structure.It is found that at ambient temperature,the phase transition from the trigonal R3c phase to the orthorhombic Pnma phase is a first-order antiferromagnetic-nonmagnetic and insulator-metal transition,and occurs at 10.56 GPa,which is in good agreement with experimental data.With increasing temperature,the transition pressure decreases almost linearly.Moreover,the thermodynamic properties including Grneisen parameter,heat capacity,entropy,and the dependences of thermal expansion coefficient on temperature and pressure are also obtained.

Phase transition and thermodynamic properties of ThO2： Quasi-harmonic approximation calculations and anharmonic effects

Formation control and obstacle avoidance for multi-agent systems have attracted more and more attention. In this paper, the problems of formation control and obstacle avoidance are investigated by means of a consensus algorithm. A novel distributed control model is proposed for the multi-agent system to form the anticipated formation as well as achieve obstacle avoidance. Based on the consensus algorithm, a distributed control function consisting of three terms(formation control term, velocity matching term, and obstacle avoidance term) is presented. By establishing a novel formation control matrix, a formation control term is constructed such that the agents can converge to consensus and reach the anticipated formation. A new obstacle avoidance function is developed by using the modified potential field approach to make sure that obstacle avoidance can be achieved whether the obstacle is in a dynamic state or a stationary state. A velocity matching term is also put forward to guarantee that the velocities of all agents converge to the same value. Furthermore, stability of the control model is proven. Simulation results are provided to demonstrate the effectiveness of the proposed control.

Phase Transitions Governed by the Fifth Power of the Golden Mean and Beyond

In this contribution results from different disciplines of science were compared to show their intimate interweaving with each other having in common the golden ratio φ respectively its fifth power φ5. The research fields cover model calculations of statistical physics associated with phase transitions, the quantum probability of two particles, new physics of everything suggested by the information relativity theory (IRT) including explanations of cosmological relevance, the ε-infinity theory, superconductivity, and the Tammes problem of the largest diameter of N non-overlapping circles on the surface of a sphere with its connection to viral morphology and crystallography. Finally, Fibonacci anyons proposed for topological quantum computation (TQC) were briefly described in comparison to the recently formulated reverse Fibonacci approach using the Janičko number sequence. An architecture applicable for a quantum computer is proposed consisting of 13-step twisted microtubules similar to tubulin microtubules of living matter. Most topics point to the omnipresence of the golden mean as the numerical dominator of our world.

Evaluation of Energy Band Gap, Thermal Conductivity, Phase Transition Temperature and Elastic Response of PS/CdS Semiconducting Optical Nanocomposite

Thick film of Polystyrene (PS)/CdS semiconducting optical nanocomposite has been synthesized by dispersing nanofiller particles of CdS in PS matrix. The nanostructure of the CdS particles has been ascertained through X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Small angle x-ray scattering analysis has been performed in order to ascertain nanocomposite character of the PS/CdS sample. Scanning Electron Microscopy (SEM) analyses of these samples have been carried out to establish the surface morphology. Optical Absorption Spectroscopy is used to measure the energy band gap of PS/CdS nanocomposite by using Tauc relation whereas Transient Plane Source Technique is used for the determination of thermal conductivity of the prepared samples. The phase transition temperature and elastic response of the prepared samples have been ascertained through Dynamic Mechanical Analyzer (DMA). This study reveals that the thermal conductivity, Young’s modulus and the toughness of the material are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanofiller particles and matrix of PS.

Phase transition,structural and thermodynamic properties of Mg_2 Si polymorphs

The plane-wave pseudo-potential method within the framework of first principles is used to investigate the structural and elastic properties of Mg2Si in its intermediate pressure （Pnma） and high pressure phases （P63/mrnc）. The lattice constants, the band structures. The bulk moduli of the Mg2Si polymorphs are presented and discussed. The phase transition from anti-cotunnite to Ni2In-type Mg2Si is successfully reproduced using a vibrational Debye-like model. The phase boundary can be described as P = 24.02994 ＋ 3.93 × 10^-3T -- 4.66816 × 10^-5T2 -- 2.2501 × 10^-9T3＋ 2.33786 × 10^-11T4. To complete the fundamental characteristics of these polymorphs we have analysed thermodynamic properties, such as thermal expansion and heat capacity, in a pressure range of 1-40 GPa and a temperature range of 0-1300 K. The obtained results tend to support the available experimental data and other theoretical results. Therefore, the present results indicate that the combination of first principles and a vibrational Debye-like model is an efficient scheme to simulate the high temperature behaviours of Mg2Si.

Phase transition, thermodynamic and elastic properties of ZrC

First principles calculation and quasi-harmonic Debye model were used to obtain more physical properties of zirconium carbide under high temperature and high pressure.The results show that the B1structure of ZrC is energetically more favorable with lower heat of formation than the B2structure,and that mechanical instability and positive heat of formation induce the inexistence of the B2structure at normal pressure.It is also found that the B1structure would transform to the B2structure under high pressure below the critical point of V/V0=0.570.In addition,various thermodynamic and elastic properties of ZrC are obtained within the temperature range of0-3000K and the pressure range of0-100GPa.The calculated results not only are discussed and understood in terms of electronic structures,but also agree well with corresponding experimental data in the literature.

Enhanced Thermoelectric Properties of Cu_(x)Se(1.75 ≤ x ≤ 2.10) during Phase Transitions

Coupling of a phase transition to electron and phonon transports provides extra degree of freedom to improve the thermoelectric performance, while the pertinent experimental and theoretical studies are still rare. Particularly,the impaction of chemical compositions and phase transition characters on the abnormal thermoelectric properties across phase transitions are largely unclear. Herein, by varying the Cu content x from 1.75 to 2.10, we systemically investigate the crystal structural evolution, phase transition features, and especially the thermoelectric properties during the phase transition for Cu_(x)Se. It is found that the addition of over-stoichiometry Cu in Cu_(x)Se could alter the phase transition characters and suppress the formation of Cu vacancies. The critical scatterings of phonons and electrons during phase transitions strongly enhance the Seebeck coefficient and diminish the thermal conductivity, leading to an ultrahigh dimensionless thermoelectric figure of merit of ~1.38 at 397 K in Cu_(2.10)Se.With the decreasing Cu content, the critical electron and phonon scattering behaviors are mitigated, and the corresponding thermoelectric performances are reduced. This work offers inspirations for understanding and tuning the thermoelectric transport properties during phase transitions.

Dielectric properties and phase transitions of La_2O_3- and Sb_2O_3-doped barium strontium titanate ceramics

The dielectric properties and phase transition characteristics of La2O3- and Sb2O3-doped barium strontium titanate ceramics prepared by solid state route were investigated. The microstructure was identified by X-ray diffraction method and scanning electron microscope was also employed to observe the surface morphologies. It is found that （La,Sb）-codoped barium strontium titanate ceramics exhibit typical perovskite structure and the average grain size decreases dramatically with increasing the content of Sb2O3. Both La3＋ ions and Sb3＋ ions occupy the A-sites in perovskite lattice. The dielectric constant and dielectric loss of barium strontium titanate based ceramics are obviously influenced by La2O3 as well as Sb2O3 addition content. The tetragonal-cubic phase transition of La2O3 modified barium strontium titanate ceramics is of second order and the Curie temperature shifts to lower value with increasing the La2O3 doping content. The phase transition of （La,Sb）-codoped barium strontium titanate ceramics diffuses and the deviation from Curie-Weiss law becomes more obvious with the increase in Sb2O3 concentration. The temperature corresponding to the dielectric constant maximum of （La,Sb）-codoped barium strontium titanate ceramics decreases with increasing the Sb2O3 content, which is attributed to the replacement of host ions by the Sb3＋ ions.

Phase transition, elastic and electronic properties of topological insulator Sb_2Te_3 under pressure: First principle study

The phase transition, elastic and electronic properties of three phases（phase Ⅰ,Ⅱ, and Ⅲ） of Sb_2Te_3 are investigated by using the generalized gradient approximation（GGA） with the PBESOL exchange–correlation functional in the framework of density-functional theory. Some basic physical parameters, such as lattice constants, bulk modulus, shear modulus,Young＇s modulus, Poisson＇s ratio, acoustic velocity, and Debye temperature Θ are calculated. The obtained lattice parameters under various pressures are consistent with experimental data. Phase transition pressures are 9.4 GPa（Ⅰ→Ⅱ） and 14.1 GPa（Ⅱ→Ⅲ）, which are in agreement with the experimental results. According to calculated elastic constants, we also discuss the ductile or brittle characters and elastic anisotropies of three phases. Phases Ⅰ and Ⅲ are brittle, while phaseⅡ is ductile. Of the three phases, phaseⅡ has the most serious degree of elastic anisotropy and phase Ⅲ has the slightest one.Finally, we investigate the partial densities of states（PDOSs） of three phases and find that the three phases possess some covalent features.

Effect of interaction and temperature on quantum phase transition in anisotropic square-octagon lattice

We investigate the effect of interaction, temperature, and anisotropic parameter on the quantum phase transitions in an anisotropic square-octagon lattice with fermions under the framework of the single band Hubbard model through using the combination of cellular dynamical mean field theory and a continuous time Monte Carlo algorithm. The competition between interaction and temperature shows that with the increase of the anisotropic parameter, the critical on-site repulsive interaction for the metal-insulator transition increases for fixed temperature. The interaction-anisotropic parameter phase diagram reveals that with the decrease of temperature, the critical anisotropic parameter for the Mott transition will increase for fixed interaction cases.

Preparation and Thermo-Responsive Properties of Poly(Oligo(Ethylene Glycol)Methacrylate)Copolymers with Hydroxy-Terminated Side Chain

Thermo-responsive random copolymers,poly(2-(2-methoxyethoxy)ethoxyethyl methacrylate-co-(ethylene glycol)methyl ether methacrylate)(P(EO_(2)-co-EO_(4/5)))and poly(2-(2-methoxyethoxy)ethoxyethyl methacrylate-co-ethylene glycol methacrylate(P(EO2-co-EG4/5))are synthesized via atom transfer radical polymerization(ATRP).The successful synthesis and the narrow polydispersity index(PDI)of two copolymers are indicated by 1H nuclear magnetic resonance(1H-NMR)and gel permeation chromatography(GPC)analyses.The transition behaviors of polymers in the aqueous solution are demonstrated by changes in turbidity and particle sizes.The transition behavior of P(EO2-co-EG4/5)is found to be milder than that of P(EO2-co-EO4/5).Moreover,the presence of hydrogen bonds without thermo-responsive properties established by hydroxyl groups in the end-side chain of P(EO_(2)-co-EG_(4/5))hinders the dehydration at the transition temperature(TT).Attenuated total reflection Fourier transform infrared spectrometry(ATR-FTIR)analysis along with contact angle measurements reveals that both P(EO_(2)-co-EO_(4/5))and P(EO_(2)-co-EG_(4/5))films undergo phase transitions from hydrophilicity to hydrophobicity above TT.By examining the swelling and collapse behaviors of the polymer films during phase transitions,it can be concluded that the end hydroxyl groups may establish hydrogen bonds with neighboring ether groups within the films,which remain intact throughout the phase transition process due to their strong bonding interactions.This leads to an increase in steric hindrance within swollen films thereby impeding dehydration processes and inducing hysteresis during phase transitions.

Tunable Electronic and Magnetic Properties from Structure Phase Transition of Layered Vanadium Diselenide

The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory（DFT）. Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.

Phase Transition and Elastic Properties of NbN under Hydrostatic Pressure

First-principles pseudopotential calculations are performed to investigate the phase transition and elastic properties of niobium nitrides （NbN）. The lattice parameters a0 and c0/a0, elastic constants Cu, bulk modulus B0, and the pressure derivative of bulk modulus B0＇ are calculated. The results are in good agreement with numerous experimental and theoretical data. The enthalpy calculations predict that NbN undergoes phase transition from NaCl-type to NiAs-type structure at 13.4 GPa with a volume collapse of about 4.0% and from AsNi-type to CW-type structure at 26.5 GPa with a volume collapse of about 7.0%. Among the four types of structures, CW-type is the most stable structure. The elastic properties are analyzed on the basis of the calculated elastic constants. Isotropic wave velocities and anisotropic elasticity of NbN are studied in detail. The longitudinal and shear-wave velocities, Vr, Vs and V increase with increasing pressure, respectively. The Debye temperature OD increases monotonically with increasing pressure except for NiAs-type structure. Both the longitudinal velocity and the shear-wave velocity increase with pressure for wave vector along all the propagation directions, except for VTA（[100]） and VTA[001]（[110]） with NaCl structure and VTA[001]（[100]） with the other three types of structures.