Effect of electric field on the smeared phase transition in crystals PbIn1/2Nb1/2O3-28PbTiO3 and PbIn1/2Nb1/2O3-37PbTiO3

The effect of a direct-current electric field (0 < E < 3 kV/cm) on the smearing of the phase transition and the Curie-Weiss exponent (γ) for two PbIn_1/2Nb_1/2O₃-28PbTiO₃ and PbIn_1/2Nb_1/2O₃-37PbTiO₃ crystals lying at different distances from the morphotropic phase boundary has been investigated. The universal Curie-Weiss law has been used to approximate the temperature dependences of the dielectric permittivity. It has been shown that the more remote is the crystal from the morphotropic phase boundary, the larger is the exponent γ and, consequently, the more smeared is the phase transition (in the zero field, γ = 1.67 and 1.49 for PbIn_1/2Nb_1/2O₃-28PbTiO₃ and PbIn_1/2Nb_1/2O₃-37PbTiO₃, respectively). It has been found that a weak electric field (no greater than 2–3 kV/cm) in the case of the more smeared phase transition almost does not affect the Curie-Weiss exponent, whereas for the PbIn_1/2Nb_1/2O₃-37PbTiO₃ crystal, this exponent decreases with increasing electric field strength and approaches γ = 1, which is characteristic of the conventional ferroelectric.     

Quadratic stark effect in the fullerene C60 at low symmetry orientation in the field

Results of numeric simulation of the influence of the electric field E = 0 ? 1 V/Å on the electronic structure of the neutral fullerene C₆₀ taking into account orientational deformation of its carbon cage at arbitrary orientations in the electric field including low symmetry orientations are presented. Splitting of the frontier t _1u - and h _u -levels of the molecule due to the quadratic Stark effect has been investigated. Dependencies of the effective electron work function and the energy gap between the lowest unoccupied and highest occupied molecular orbitals on the strengths of the electric field have been determined.     

Influence of a magnetic field on the mutual rectification of alternating currents induced by electromagnetic waves in graphene

The direct component of the electric current induced in graphene placed in a constant magnetic field has been found in the case where two electromagnetic waves with two mutually perpendicular planes of polarization are normally incident on the surface of the sample. It has been demonstrated that the direct component of the current along the direction of the electric field vector of the wave with the frequency ω₁ arises only when the ratio between the frequencies of the incident waves is ω₁/ω₂ = 2 or 1/2. In the latter case, the direct current component appears only in the presence of a magnetic field.     

Electric quadrupole orientation in zinc. The variation of electric field gradient with atomic number through the 4sp series

Using the top-loading PrNi₅ nuclear demagnetisation stage /1/ to reach temperatures close to 1mK, electric quadrupole orientation of trace 4sp series impurities in zinc has been measured. Results establish the variation of the electric field gradient at impurity nuclei in this series and also yield the ratio of the electric quadrupole moments of⁷¹As and⁷²As.     

Transient energy transfer between writing beams during hologram formation in Bi12GeO20

A large transient energy transfer between writing beams during volume phase-hologram formation in Bi₁₂GeO₂₀ has been observed. The variation of the energy transfer by applying an external field and by changing the fringe spacing of the elementary holograms have been measured and described in the framework of Kukhtarevs nonlinear theory of transient self-diffraction. The results indicate that the transient energy transfer in Bi₁₂GeO₂₀ is due to a non-stationary phase mismatch between the intensity- and refractive index grating caused by photoconductivity and that the transient energy transfer increases with increasing fringe spacing and increasing applied electric field. Up to ten-fold amplification of coherent beams has been measured, corresponding to an exponential gain of Г = 2 cm^-1. A continuous energy transfer has been observed when the phase between recording beams was changed linearly with time during recording. It is shown that light is coherently amplified for electric field strengths larger than 2.3 kV/cm and that a peak amplification factor of Г₁ = 2 cm^-1 has been reached for E₀ = 11 kV/cm.     

A boundary-value problem for dielectric spherical void in a homogeneous insulator by considering surface conductivity

In this paper, the boundary-value problem satisfying the Dirichlet condition has been solved for the case of a dielectric, spherical void inside a homogeneous insulator by considering surface conductivity. Mathematical equations have been derived to calculate the respective electric fields E_i(t)and E_e(t) inside and outside spherical gas voids that exist within an insulator by considering the surface conductivity γ_s of gas voids having an electric permittivity of ε_i and conductivity γ_i under DC (ωτ⪡1) and AC (ωτ⪢1) conditions. The expression for the dipole moment of a polarized spherical dielectric particle has been obtained in accordance with the determined electric field E_i(t). The derived expressions are then applied to calculate reciprocal interaction force between the spherical particle and metallic electrodes, which is very considerable for the dielectric separation processes in the DC and AC cases.     

Phase transitions and optical properties in 〈001〉 (1−<Emphasis Type="Italic">x</Emphasis>)PbZn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript>−<Emphasis Type="Italic">x</Emphasis>PbTiO<Subscript>3</Subscript> single crystals

The effect of a constant electric field (0 < E < 5 kV/cm) on the optical properties of PbZn_1/3Nb_2/3O₃?xPbTiO₃ (PZN-xPT) crystals with x = 7 and 9% has been analyzed. It has been shown that, at temperatures close to the temperature of the transition from the rhombohedral [R(X)] phase to the tetragonal (T) phase, two induced phase transitions are observed in the electric field, which are associated with the appearance of new intermediate phases M_a and M_c [R(X)-M_a-M_c-T]. Correlation between these two transitions and the PbTiO₃ content x has been found. The E-T phase diagrams have been obtained. The M_c phase in PZN-9PT crystals is found to remain the ground state after the removal of the electric field, whereas the M_c phase in PZN-7PT crystals is metastable and is transformed into the M_a phase after the removal of the electric field.     

Phase transitions and spin excitations in new multiferroics with modulated magnetic structure

Coexistence of an antiferromagnetic (modulated) structure and electric polarization has been revealed in single crystals of Eu_{1 ? x} Y_xMnO₃ (0.2 ≤ x ≤ 0.5) and Gd_{1 ? x} Y_xMnO₃ (0 ≤ x ≤ 0.2) manganites. Hence, these compounds can be considered as a new family of multiferroics. Various phase transitions, both spontaneous and induced by magnetic fields up to 250 kOe, accompanied by anomalies in magnetization, magnetostriction, permittivity, and electric polarization, have been found, and phase T-x diagrams have been constructed. In the submillimeter range (8–40 cm^?1), new spin excitations—electromagnons—have been revealed; they are excited by an electric field. It is established that suppression of the modulated structure by a magnetic field leads to the disappearance of electromagnons; this process is accompanied by significant changes in the permittivity in a wide frequency range.     

Electro-optic effect in SrTiO3 and Sr1–x Ca x TiO3 (x = 0.014)

The results of the investigation of the quadratic electro-optic effect in Sr_1–x Ca _x TiO₃ with x = 0.014 (SCT) and in nominally pure SrTiO₃ (STO) at room temperature in applied direct-current (dc) and alternating-current (ac) electric fields have been presented. It has been shown that the quadratic (in polarization) electro-optic coefficients of STO and SCT crystals coincide within the accuracy of the determination (±5%). It has been found that, in nominally pure STO measured in a dc electric field, there is a relaxation of the electro-optic effect with a relaxation time τ ≈ 30 s due to the formation of a space charge in the sample. No similar effect in SCT has been observed. A possible mechanism for the formation of a space charge in STO and SCT has been discussed.     

Ab initio investigation of the electronic and vibrational properties for the (CaLi)+ ionic molecule

A wide adiabatic study has been performed for numerous electronic states of CaLi⁺ molecular ion. The adiabatic potential energy curves and their spectroscopic constants (R_e, D_e, ω_e and T_e) have been calculated using an ab initio approach including a nonempirical pseudo-potential for the Ca and Li cores with the core polarisation potentials operator through full configuration interaction (FCI). Thereafter, the energies of vibrational levels and their spacing for all these states have been reported. In addition, the electric dipole moment curves have been investigated for the (1-19) Σ, (1-12) Π and (1-8) Δ electric states. Moreover it lets us check the extreme transition dipole moments (TDM). These behaviours of TDM are more accustomed to estimate the radiative lifetimes for all vibrational levels in 2¹Σ⁺ and 3¹Σ⁺ states. Also, the bound-bound and the bound-free contribution have been calculated precisely and by employing a Franck–Condon (FC) approximation.     

Parametric instability in a two-hole species semiconductor-plasma

The parametric excitation of a low frequency wave has been investigated analytically in a two-hole species semiconductor-plasma in the region of kl ? 1 using the hydrodynamic model of the plasmas in the presence of a high frequency oscillatory electric field (E₀ cos ω₀t applied along the X-axis) and a d.c. magnetic field B₀ normal to the electric field (along the Z-axis), the low frequency wave propagating in the X–Z plane making a very small angle θ with the X-axis. The system supports a purely growing unstable mode. The variation of the growth rate of the unstable mode has been studied over a wide range of system parameters for the specific case of an intrinsic GaAs crystal at 300 K. The oscillatory electric field can be obtained by irradiating the crystal with a 119μm H₂O laser.     

Optical and acoustic properties of 33PbIn1/2Nb1/2O3-35PbMg1/3Nb2/3O3-32PbTiO3 single crystals in an electric field

The influence of different conditions of applying a dc electric field (0 < E < 4 kV/cm) on the behavior of optical transmission and on the acoustic parameters (sound velocity and attenuation) in the [001]- and [011]-oriented single crystals 33Pb(In_1/2Nb_1/2)O₃-35PbMg_1/3Nb_2/3O₃-32PbTiO₃ existing near the morphotropic phase boundary has been investigated. It has been found that the optical transmission, sound velocity, and attenuation sharply change near the phase transition in a narrow range of electric fields for any method of their applying. In the field applied along [001], the change in the sound velocity due to the phase transition is 1.5 times greater than that in the field applied along [011]. This is caused by a larger contribution of the piezoelectric effect to the elastic modulus determining the sound velocity along [001] as compared to [011]. It has been shown that the number, symmetry, and stability of the phases formed in the field depend on the conditions of applying the field.     

Theory of resonant forbidden Raman scattering in semiconductors

The Raman tensors for the electric field-induced and wavevector dependent scattering from LO phonons in semiconductors have been calculated near critical points using a perturbation treatment. The resulting expressions have analytic closed forms such that the dependence of the forbidden scattering intensity on the incident photon energy and the applied d.c. electric field can be evaluated from available energy band parameters. The forbidden LO scattering intensity of GaAs in the back scattering configuration has been numerically calculated near the e₁ and E₁ gaps as functions of the incident photon energy and the dc electric field. The result shows strong interference between the two scattering processes. The allowed TO and LO Raman scattering intensities of GaAs were also calculated at a wavelength of 1.06 μm from the SHG and Faust-Henry coefficients, and compared with the forbidden LO intensity.     

Parametric excitation of acoustohelicon waves in a piezoelectric semiconductor

The parametric excitation of acoustohelicon waves has been studied in a piezoelectric semiconductor in the presence of a strong high frequency oscillatory electric field. The threshold electric field amplitude and the growth rate of the unstable mode have been obtained analytically and for n-InSb at 77 K the unstable mode is found to be propagating with a growth rate ～10³ s^?1 when the crystal is irradiated with a 10.6 μm CO₂ laser.     

Measurement of electron energy and density in an H. F. electrodeless ring discharge

The electron temperatureT _e and the electron density were measured as functions of the radial distance in a 10 Mc/s electrodeless ring discharge in hydrogen in the pressure range 0.1–0.3 Torr. It was found thatT _e remains nearly constant along the radius of the cylindrical vessel. The measured values ofT _e have been compared with those observed by other workers and an estimate of the effective electric field in the discharge has been made. From this estimate it has been inferred that even after the first stage of the ring discharge is well established the longitudinal component of the electric field remains of considerable importance. The radial density distribution of the electrons was found to be different from those in an uniform electric field. This deviation in the radial density distribution has been attributed to the influence of the azimuthal electric field.     

Linear electric shift in the paramagnetic resonance of Mn2+ in ZnTe

The influence of an electric field on the EPR transition has been observed in ZnTe:Mn²⁺ at 29 K by applying an ac electric field. The value of the component of the third rank tensor describing the effect is R₁₄ = 164 HzV^-1 cm. A strong correlation between the magnitude of the component R₁₄ and the amount of covalency was found.     

外电场作用下Si_2O分子的激发特性

主要对2种Si2O分子异构体的激发特性进行研究,由计算结果可知,外电场对Si2O分子的激发能,振子强度,跃迁偶极矩及吸收光谱有着显著的影响.无外电场时三角型Si2O(C2v,1A1)分子在可见光区无吸收谱,外电场作用下其在可见光区(407.18—526.93nm)有比较弱的吸收谱.直线型Si-Si-O(C∞v,3Σ-)分子在有无外电场作用时在蓝光和紫光区均有一定的吸收谱,其中比较难得的是在蓝色光区(478.88—488.59nm)呈现较强的吸收谱.     

Investigation of quadratic stark effect on Rb D<Subscript>2</Subscript> atomic line

Experimental study of the influence of an electric field on the atomic hfs levels of D₂ line of Rb atom, transitions 5S _1/2 ? 5P _3/2, has been performed. For this purpose a sapphire cell with internal electrodes used to produce a constant electric field was elaborated. By using the saturation absorption technique the frequency shifts of all 12 atomic D₂ line transitions were recorded. The results are compared with the theory.     

The study of Mössbauer effect in EuBa2Cu3O7-y

EuBa₂(Cu_1-xFe_x)₃O_7-x has been investigated by the⁵⁷Fe and¹⁵¹Eu Mössbauer effect. The⁵⁷Fe Mössbauer spectra of the EuBa₂(Cu_1xFe_x)₃O_7-y without or with DC electric current (the current strength I=0.5A) around the superconducting transition temperature have been measured. The results indicate that the isomer shift (IS) and the quadrupole splitting (QS) of the Fe replacing the Cu(2) vary neither with increasing the Fe content nor with the small DC eletric, current passing the superconductor and that the IS and the QS of the Fe replacing the Cu(1) vary with the Fe content. Especially, the IS and the QS of the Fe (D3) replacing the Cu(1) are changed when the small electric current passes the superconductor at 80K.     

Electroabsorption near the 1S line of the green series of Cu2O

The effect of an electric field on the n = 1 line of the green series of Cu₂O has been studies at 4.2°K, using single crystals, polarized light and a modulation technique. Under the action of an electric field, an ignition of this line (λ^g_1S = 5 830 Å) is observed. This ignition effect depends on the geometry of the experiments, and gives informations on the nature of this transition as well as on the bands involved in the formation of this exciton.