In the frame of the basic quantum theory,from the one-dimensional infinite-height half-wall quantum potential well with time-dependent boundary conditions and from the three-dimensional finite-depth sphere-square potential well with time-dependent boundary conditions we constructed two kinds of new Hamiltonian operators separately which describe electric particle interacting with eletromagnetic field.In the adiabatic approximation are calculated the complex Berry phases of two kinds of new systems.
In the frame of the basic quantum theory,from the one-dimensional infinite-height half-wall quantum potential well with time-dependent boundary conditions and from the three-dimensional finite-depth sphere-square potential well with time-dependent boundary conditions we constructed two kinds of new Hamiltonian operators separately which describe electric particle interacting with eletromagnetic field.In the adiabatic approximation are calculated the complex Berry phases of two kinds of new systems.
A reasonable dissociation limit of B″3Πu state of molecular sulfur (S2) has been derived,and a potential energy curve of B″3Πu and X3Σ-g states of S2 has been calculated by using Gaussian 94 QCISD(T) method and the 6-311++G** basic set function.The murrell-Sorbie potential energy function and spectrum constants are given.Because B″3Πu state overlap extensively with B3Σ-u state in the repulse branch and B″3Πu and X3Σ-g states have the same dissociate limits,they have an overlap in the attract branch.In this paper,the interaction characteristics of B″3Πu,B3Σ-u and X3Σ-g states have also been discussed.
A reasonable dissociation limit of B″3Πu state of molecular sulfur (S2) has been derived,and a potential energy curve of B″3Πu and X3Σ-g states of S2 has been calculated by using Gaussian 94 QCISD(T) method and the 6-311++G** basic set function.The murrell-Sorbie potential energy function and spectrum constants are given.Because B″3Πu state overlap extensively with B3Σ-u state in the repulse branch and B″3Πu and X3Σ-g states have the same dissociate limits,they have an overlap in the attract branch.In this paper,the interaction characteristics of B″3Πu,B3Σ-u and X3Σ-g states have also been discussed.
The differential cross-section and parameters of polarization in electron-atom(Na) collision are calculated by the Distorted Wave Method(DWM) in this work.The results are compared with those of experiment and those obtained by Convergent Closed Coupling(CCC) method.It is shown that the DWM is a reliable method with a clear model in moderate to high energy region (5—10 times of threshold energy).
The differential cross-section and parameters of polarization in electron-atom(Na) collision are calculated by the Distorted Wave Method(DWM) in this work.The results are compared with those of experiment and those obtained by Convergent Closed Coupling(CCC) method.It is shown that the DWM is a reliable method with a clear model in moderate to high energy region (5—10 times of threshold energy).
A generalized Bethe analytic formula for dipole-excited collision strengths is suggested, in which a cut-off k0 in the momentum transfer, a threshold (via extrapolation) and a thrice threshold of collision strengths for each dipole-excited process are calculated quickly based on the quasi-relativistic plane wave Born (QRPB) and distorted wave (QRDW) methods respectively. The formula can be applied to moderate and low impact electron energies. As a example, dipole collision strengths and corresponding rate coefficients of Au50+ are given at all impact energies, which are in agreement with that of a least-square spline method. Meanwhile the systems of k0 in channel n0l0→n(l0+1) are analyzed.
A generalized Bethe analytic formula for dipole-excited collision strengths is suggested, in which a cut-off k0 in the momentum transfer, a threshold (via extrapolation) and a thrice threshold of collision strengths for each dipole-excited process are calculated quickly based on the quasi-relativistic plane wave Born (QRPB) and distorted wave (QRDW) methods respectively. The formula can be applied to moderate and low impact electron energies. As a example, dipole collision strengths and corresponding rate coefficients of Au50+ are given at all impact energies, which are in agreement with that of a least-square spline method. Meanwhile the systems of k0 in channel n0l0→n(l0+1) are analyzed.
It is shown that the electron impact with argon excitation out of the metastable to the 3p54p levels is very important for spectrum,laser physics and plasma processing.Analysis of the cross sections of 3p54p,J=3 level in mainfolds of 3p54p is valuable.It also provides the atomic character of emission harmonics in intense laser field.
It is shown that the electron impact with argon excitation out of the metastable to the 3p54p levels is very important for spectrum,laser physics and plasma processing.Analysis of the cross sections of 3p54p,J=3 level in mainfolds of 3p54p is valuable.It also provides the atomic character of emission harmonics in intense laser field.
The configuration of a semimonolithic continuous nondegenerate optical parameter oscillator consisting of an α-cut KTP crystal pumped by an intracavity frequency-doubled and frequency-stabilized Nd∶YAP laser is designed. Both two-mode quadrature-phase squeezing of 3.7dB and intensity-difference squeezing of 7dB have been generated from the cw-NOPO operating respectively below and above the oscillation threshold. The system can operate stably to generate the squeezed light for over half an hour.
The configuration of a semimonolithic continuous nondegenerate optical parameter oscillator consisting of an α-cut KTP crystal pumped by an intracavity frequency-doubled and frequency-stabilized Nd∶YAP laser is designed. Both two-mode quadrature-phase squeezing of 3.7dB and intensity-difference squeezing of 7dB have been generated from the cw-NOPO operating respectively below and above the oscillation threshold. The system can operate stably to generate the squeezed light for over half an hour.
Photon noise squeezing and its physical mechanism of a driven V-type three-level laser are investigated via Scully-Lamb theory.It is shown that intracavity squeezing of 10% and extracavity squeezing of 20% can be achieved.Even if the amount of squeezing in V system is smaller than that in Λ system (intracavity squeezing and extracavity squeezing of up to 50%),both systems have the same mechanism responsible for the squeezing of photon noise.
Photon noise squeezing and its physical mechanism of a driven V-type three-level laser are investigated via Scully-Lamb theory.It is shown that intracavity squeezing of 10% and extracavity squeezing of 20% can be achieved.Even if the amount of squeezing in V system is smaller than that in Λ system (intracavity squeezing and extracavity squeezing of up to 50%),both systems have the same mechanism responsible for the squeezing of photon noise.
A quantum theoretical model for the system of interaction between two beams and N atoms of Λ-type three-level has been established.The dynamical behavior and the features of the optical quantum non-demolition (QND) measurement are discussed in details.The results show that the efficient QND measurement can be well performed at the operation of the nonlinear double-resonance for two beams.
A quantum theoretical model for the system of interaction between two beams and N atoms of Λ-type three-level has been established.The dynamical behavior and the features of the optical quantum non-demolition (QND) measurement are discussed in details.The results show that the efficient QND measurement can be well performed at the operation of the nonlinear double-resonance for two beams.
We have studied the photon echo in ultrafast modulation spectroscopy in a cascade three-level system (UMSCTS).When the pump beams have broadband linewidth,the one-photon and two-photon four-wave mixings are related to the three-pulse stimulated photon echo and sum-frenquency three-level echo when τ＞0,respectively;while the result should coincide with the case that the beams have narrow linewidth when τ＜0.
We have studied the photon echo in ultrafast modulation spectroscopy in a cascade three-level system (UMSCTS).When the pump beams have broadband linewidth,the one-photon and two-photon four-wave mixings are related to the three-pulse stimulated photon echo and sum-frenquency three-level echo when τ＞0,respectively;while the result should coincide with the case that the beams have narrow linewidth when τ＜0.
Circular Couette System has served as a paradigm for studying complex transitions to turbulence,the influence of finite geometry on pattern-selection mechanisms.In this paper stability of a circular Couette system with the intermediate radius ratio is investigated through laboratory experiments and computer simulation.The classical Rayleigh centrifugal instability theory is extended to general viscous,incompressible fluid between concentric independently rotating cylinders.A criterion of stability is formulated to quantitatively determine the stability boundary.The laboratory experiments employ the techniques of the laser light scattering and the flow visualization.The apparatus has a radius ratio of η=0.699 and an aspect ratio of Γ=18.A striking feature in phase diagram of flow states is the novel primary instability:when the outer cylinder is at rest,or counterrotating,instability occurs first for nonzero azimuthal wave number.Instead of time-independent Taylor vortex flow,the resulting flow is spiral vortices which are traveling waves in both the axial and azimuthal directions.Preliminary experimental measurements of transition Reynolds numbers presented here are in agreement with those obtained numerically.Laboratory and numerical experiments have revealed the effects of radius ratio on pattern formation,the sequence of transitions.
Circular Couette System has served as a paradigm for studying complex transitions to turbulence,the influence of finite geometry on pattern-selection mechanisms.In this paper stability of a circular Couette system with the intermediate radius ratio is investigated through laboratory experiments and computer simulation.The classical Rayleigh centrifugal instability theory is extended to general viscous,incompressible fluid between concentric independently rotating cylinders.A criterion of stability is formulated to quantitatively determine the stability boundary.The laboratory experiments employ the techniques of the laser light scattering and the flow visualization.The apparatus has a radius ratio of η=0.699 and an aspect ratio of Γ=18.A striking feature in phase diagram of flow states is the novel primary instability:when the outer cylinder is at rest,or counterrotating,instability occurs first for nonzero azimuthal wave number.Instead of time-independent Taylor vortex flow,the resulting flow is spiral vortices which are traveling waves in both the axial and azimuthal directions.Preliminary experimental measurements of transition Reynolds numbers presented here are in agreement with those obtained numerically.Laboratory and numerical experiments have revealed the effects of radius ratio on pattern formation,the sequence of transitions.
In this paper,the electron motion confined by a transverse magnetic field in a hollow-cathode discharge is investigated.Some swarm paramaters are obtained such as the energy and spatial distribution under the terminative condition.Due to the existence of a transverse magnetic field,electrons' motion is changed and thus all kinds of the inelastic collision are different from the case of zero magnetic field.The results from simulation show that while the magnetic field is equal to 0.05T,the ionization increases and the distribution of the electrons and ions are of benifit to the development of ion laser.
In this paper,the electron motion confined by a transverse magnetic field in a hollow-cathode discharge is investigated.Some swarm paramaters are obtained such as the energy and spatial distribution under the terminative condition.Due to the existence of a transverse magnetic field,electrons' motion is changed and thus all kinds of the inelastic collision are different from the case of zero magnetic field.The results from simulation show that while the magnetic field is equal to 0.05T,the ionization increases and the distribution of the electrons and ions are of benifit to the development of ion laser.
The problem of the surface-pressure-induced separation of chiral phases in monolayer of racemic amphiphiles is studied.Following the work of Ou-Yang and his co-wokers published in “Chem.Phys.Lett.(1998)”,we give several classes of classical solutions in the two-dimensional case for the equilibrium equations for the chiral phases separation order parameter and the molecular orientation pattern.
The problem of the surface-pressure-induced separation of chiral phases in monolayer of racemic amphiphiles is studied.Following the work of Ou-Yang and his co-wokers published in “Chem.Phys.Lett.(1998)”,we give several classes of classical solutions in the two-dimensional case for the equilibrium equations for the chiral phases separation order parameter and the molecular orientation pattern.
Ferroelectric ultrafine particles were fabricated with LB film technique. The experimental results showed: The ferroelectric ultrafine particles were stable with a higher coverage ratio, and had a dielectric confinement effect in the LB films. The LB film showed photoluminescence at room temperature. The fluorescence spectrum consisted of wide luminescence bands. The emission spectrum had up-conversion.
Ferroelectric ultrafine particles were fabricated with LB film technique. The experimental results showed: The ferroelectric ultrafine particles were stable with a higher coverage ratio, and had a dielectric confinement effect in the LB films. The LB film showed photoluminescence at room temperature. The fluorescence spectrum consisted of wide luminescence bands. The emission spectrum had up-conversion.
AlL and OK near edge fine structures in sapphire are studied using electron energy loss microspectroscopy in a transmission electron microscope;an analysis of the electronic populations of atoms Al and O,and a comparison between different partial cross sections are given.We consider the ionization of an atom in a homogeneous solid to interpret the elemental effects in the ionization region near edges.The chemical effects in the region near edge onset are interpreted by using extended Hückel molecular orbital theory and Bloch's theorem including the effects of translation symmetry in crystals to calculate the electronic transitions from core-shell to unoccupied valence-shell.We also consider the additional chemical effects, which arise from the elastic backscattering of the atomic ionization waves by the atoms neighboring the exited atom,giving rise to the so-called extended fine structure in the ionization region.The agreement between the calculated results and the experimental energy loss spectra of sapphire from single-phase region is good.
AlL and OK near edge fine structures in sapphire are studied using electron energy loss microspectroscopy in a transmission electron microscope;an analysis of the electronic populations of atoms Al and O,and a comparison between different partial cross sections are given.We consider the ionization of an atom in a homogeneous solid to interpret the elemental effects in the ionization region near edges.The chemical effects in the region near edge onset are interpreted by using extended Hückel molecular orbital theory and Bloch's theorem including the effects of translation symmetry in crystals to calculate the electronic transitions from core-shell to unoccupied valence-shell.We also consider the additional chemical effects, which arise from the elastic backscattering of the atomic ionization waves by the atoms neighboring the exited atom,giving rise to the so-called extended fine structure in the ionization region.The agreement between the calculated results and the experimental energy loss spectra of sapphire from single-phase region is good.
Based on the tight binding scattering theoretical method ,the electronic structure of As adsorption on the surface of InP(110) is studied.The bulk material is described by a realistic empirical tight binding Hamiltonians ,the translationally invariant As/InP(110)(1×1) system is discussed in terms of the ordered As monolayer and an exchange reaction between surface P and As adatoms. Surface states and surface resonances are identified from the calculated local density of states along the four zone boundaries of the (110) surface Brillouin zone .In this calculation ,some ETB parameters are adjusted at the surface, the results are in good agreement with the experiment and are better than other theoretical results.
Based on the tight binding scattering theoretical method ,the electronic structure of As adsorption on the surface of InP(110) is studied.The bulk material is described by a realistic empirical tight binding Hamiltonians ,the translationally invariant As/InP(110)(1×1) system is discussed in terms of the ordered As monolayer and an exchange reaction between surface P and As adatoms. Surface states and surface resonances are identified from the calculated local density of states along the four zone boundaries of the (110) surface Brillouin zone .In this calculation ,some ETB parameters are adjusted at the surface, the results are in good agreement with the experiment and are better than other theoretical results.
We present results of a theoretical calculation of the electronic structure of the two polar ZnSe/GaAs(100) interfaces. The bulk electronic structure is described by the nearest neighbor tight binding formalism. Using the scattering theoretical method, we have obtained wave vector-resolved interface layer densities of states and the interface band structure. For both Se/Ga and As/Zn interfaces, there exist no interface states in the fundamental gap, but there are three interface bands and four semi-resonance bands in the valence-band region. Finally, we study the nature and origins of these bands by analysing orbital-resolved layer densities of states.
We present results of a theoretical calculation of the electronic structure of the two polar ZnSe/GaAs(100) interfaces. The bulk electronic structure is described by the nearest neighbor tight binding formalism. Using the scattering theoretical method, we have obtained wave vector-resolved interface layer densities of states and the interface band structure. For both Se/Ga and As/Zn interfaces, there exist no interface states in the fundamental gap, but there are three interface bands and four semi-resonance bands in the valence-band region. Finally, we study the nature and origins of these bands by analysing orbital-resolved layer densities of states.
The new bulk superconductors of Pr1-xCaxBa2Cu3O1-δ (0.4≤x≤0.6) have been synthesized under high pressure for the first time to our knowledge. The highest Tc of 98K was observed for Oxygen-deficient tetragonal Pr0.5Ca0.5Ba2Cu3O7-δ sample. Our results demonstrate the valence state of Pr in 123 structure is a mixed sate greater than 3+, hole filling and hybridization are the primary cause of the suppression of superconductivity by Pr in 123 structure.
The new bulk superconductors of Pr1-xCaxBa2Cu3O1-δ (0.4≤x≤0.6) have been synthesized under high pressure for the first time to our knowledge. The highest Tc of 98K was observed for Oxygen-deficient tetragonal Pr0.5Ca0.5Ba2Cu3O7-δ sample. Our results demonstrate the valence state of Pr in 123 structure is a mixed sate greater than 3+, hole filling and hybridization are the primary cause of the suppression of superconductivity by Pr in 123 structure.
The temperature dependence of the resistivity of an epitaxial YBa2Cu3O7-δ thin film has been measured in various magnetic fields up to 7T applied parallel to the c-axis near Tc. The result shows that the resistivity below Tc can be well fitted by thermally activation flux motion. The current density dependence of the effective pinning potential follows a logarithmic law proposed by Zeldov et al. The temperature and magnetic field dependence of the effective pinning potential follows U(H,T)=U0(1-T/Tc)H-α, with α=0.63, showing 2D behavior, It is consistent with the plastic deformation model of the flux-line lattice at flux-line-lattice dislocations.
The temperature dependence of the resistivity of an epitaxial YBa2Cu3O7-δ thin film has been measured in various magnetic fields up to 7T applied parallel to the c-axis near Tc. The result shows that the resistivity below Tc can be well fitted by thermally activation flux motion. The current density dependence of the effective pinning potential follows a logarithmic law proposed by Zeldov et al. The temperature and magnetic field dependence of the effective pinning potential follows U(H,T)=U0(1-T/Tc)H-α, with α=0.63, showing 2D behavior, It is consistent with the plastic deformation model of the flux-line lattice at flux-line-lattice dislocations.
We have prepared antiferroelectric ceramics with compositions of (Pb0.97La0.02)(Zr1-x-ySnyTix)O3(x=0.09 or 0.1; 0.16≤y≤0.38) near antiferroelectric (AFE)tetragonal-ferroelectric (FE)rhombohedral morphotropic phase boundary. The effects of Sn content on electric field-induced AFE→FE switching field Ec, double-hysteresis-loop width ΔE, and temperature-induced FE→AFE phase transition temperature TFE, AFE→paraelectric (PE) transition temperature Tc are investigated. At constant Ti content x, both TEF and Tc decrease with increase of Sn content y. Electric hysteresis loop measurement demonstrates an increase of Ec and decrease of ΔE when Sn content y increases. Furthermore, we also find that Ec and ΔE are related with TFE and Tc. In situ X-ray diffraction under dc bias field shows that symmetry changes from tetragonal phase to rhombohedral phase with an increase of c axis,and an increase of lattice volume.
We have prepared antiferroelectric ceramics with compositions of (Pb0.97La0.02)(Zr1-x-ySnyTix)O3(x=0.09 or 0.1; 0.16≤y≤0.38) near antiferroelectric (AFE)tetragonal-ferroelectric (FE)rhombohedral morphotropic phase boundary. The effects of Sn content on electric field-induced AFE→FE switching field Ec, double-hysteresis-loop width ΔE, and temperature-induced FE→AFE phase transition temperature TFE, AFE→paraelectric (PE) transition temperature Tc are investigated. At constant Ti content x, both TEF and Tc decrease with increase of Sn content y. Electric hysteresis loop measurement demonstrates an increase of Ec and decrease of ΔE when Sn content y increases. Furthermore, we also find that Ec and ΔE are related with TFE and Tc. In situ X-ray diffraction under dc bias field shows that symmetry changes from tetragonal phase to rhombohedral phase with an increase of c axis,and an increase of lattice volume.
The valence electron densities of bulk and microdefects in binary FeAl, and FeAl doping with B,Zr or Si have been calculated by using the positron lifetime parameters of the alloys. The density of valence electron is low in the bulk of FeAl alloy. It indicates that, in Fe atom the 3d electrons have well-localized properties and tend to form covalent bonds with Al atoms, thus the bonding nature in FeAl is a mixture of metallic and covalent. The large-open-volume defects occur in grain boundaries in FeAl and the cohesion of the grain boundaries is weak due to the low density of valence electron there. When a small amount of B atoms is added into FeAl alloy, some of B atoms segregate to the grain boundaries and increase the valence electron density; this will strengthen the bonding cohesion in the grain boundaries. The other B atoms are dissolved interstitially into the bulk, they interact with Fe and Al, increase the density of valence electrons and thus the bonding cohesion in the bulk. The addition of Zr into FeAl results in the increase of the density of valence electrons in the bulk and grain boundary. Whereas, if FeAl is alloyed with Si, the density of valence electrons in the grain boundary will decrease. B and Zr are found to be beneficial elements for improving the brittleness of FeAl alloy, while Si exhibits an opposite effect.
The valence electron densities of bulk and microdefects in binary FeAl, and FeAl doping with B,Zr or Si have been calculated by using the positron lifetime parameters of the alloys. The density of valence electron is low in the bulk of FeAl alloy. It indicates that, in Fe atom the 3d electrons have well-localized properties and tend to form covalent bonds with Al atoms, thus the bonding nature in FeAl is a mixture of metallic and covalent. The large-open-volume defects occur in grain boundaries in FeAl and the cohesion of the grain boundaries is weak due to the low density of valence electron there. When a small amount of B atoms is added into FeAl alloy, some of B atoms segregate to the grain boundaries and increase the valence electron density; this will strengthen the bonding cohesion in the grain boundaries. The other B atoms are dissolved interstitially into the bulk, they interact with Fe and Al, increase the density of valence electrons and thus the bonding cohesion in the bulk. The addition of Zr into FeAl results in the increase of the density of valence electrons in the bulk and grain boundary. Whereas, if FeAl is alloyed with Si, the density of valence electrons in the grain boundary will decrease. B and Zr are found to be beneficial elements for improving the brittleness of FeAl alloy, while Si exhibits an opposite effect.
Erbium-doped SiOx is prepared by molecular beam epitaxy. The influence of Er on the incorporation of O is studied by using Auger specstrocopy. Photoluminescence(PL) peaks around the wavelength of 1.53μm have been observed within the temperature range of 18 to 300 K after annealing. The relationship between PL intensity and annealing temperature is discussed. The temperature dependence of the PL intensity shows an exponential decay with an activation energy of 12 meV at low temperatures (＜100 K) and 150 meV at high temperatures (＞100K).
Erbium-doped SiOx is prepared by molecular beam epitaxy. The influence of Er on the incorporation of O is studied by using Auger specstrocopy. Photoluminescence(PL) peaks around the wavelength of 1.53μm have been observed within the temperature range of 18 to 300 K after annealing. The relationship between PL intensity and annealing temperature is discussed. The temperature dependence of the PL intensity shows an exponential decay with an activation energy of 12 meV at low temperatures (＜100 K) and 150 meV at high temperatures (＞100K).
The photoluminescence (PL) spectra from p-type α-porous silicon carbides prepared under UV photo-assisted process and under dark-current condition are investigated in detail. Emission bands with peak energies of 2.35, 2.50,2.70, and 3.43 are resolved. The PL stability in time and the PL difference arising from different tuning excitation energies are studied. It is found that the PL spectra of the α-porous silicon carbide depend strongly on the preparation conditions for electrochemical etching. The PL spectrum of the sample prepared under photo-assisted process has an enhancement on the lower-energy side of the emission; on the contray, another one under dark-current condition has an enhancement at the higher energy side, and the former stability is better than the latter one, and the latter PL intensity decreases with the increase of the time in the air. The reasons about these differences are discussed.
The photoluminescence (PL) spectra from p-type α-porous silicon carbides prepared under UV photo-assisted process and under dark-current condition are investigated in detail. Emission bands with peak energies of 2.35, 2.50,2.70, and 3.43 are resolved. The PL stability in time and the PL difference arising from different tuning excitation energies are studied. It is found that the PL spectra of the α-porous silicon carbide depend strongly on the preparation conditions for electrochemical etching. The PL spectrum of the sample prepared under photo-assisted process has an enhancement on the lower-energy side of the emission; on the contray, another one under dark-current condition has an enhancement at the higher energy side, and the former stability is better than the latter one, and the latter PL intensity decreases with the increase of the time in the air. The reasons about these differences are discussed.
In recent years, the electrocaloric effect (abbr. ECE) of dielectrics has attracted attention for ferroelectric refrigerating application. The fundamentals of ferroelectric refrigeration and the expressions of three types of ECEs, i.e., linear, quadratic and field-induced first-order phase transition electrocaloric effects, are presented in this paper. The ECE properties of (1-x)PbMg1/3Nb2/3O3-xPbTiO3［abbr. (1-x)PMN-xPT］ ferroelectric ceramics(x=0.08, 0.10, and 0.25 respectively) at room temperature were measured and analyzed. It is found that the large electrocaloric effect of (1-x)PMN-xPT ferroelectric ceramics about room temperature is due to the electric-induced first-order phase transition and linear electrocaloric effects, and these ceramics could be used in ferroelectric multi-stage refrigeration.
In recent years, the electrocaloric effect (abbr. ECE) of dielectrics has attracted attention for ferroelectric refrigerating application. The fundamentals of ferroelectric refrigeration and the expressions of three types of ECEs, i.e., linear, quadratic and field-induced first-order phase transition electrocaloric effects, are presented in this paper. The ECE properties of (1-x)PbMg1/3Nb2/3O3-xPbTiO3［abbr. (1-x)PMN-xPT］ ferroelectric ceramics(x=0.08, 0.10, and 0.25 respectively) at room temperature were measured and analyzed. It is found that the large electrocaloric effect of (1-x)PMN-xPT ferroelectric ceramics about room temperature is due to the electric-induced first-order phase transition and linear electrocaloric effects, and these ceramics could be used in ferroelectric multi-stage refrigeration.