Barium doping-induced polar nanoregions in lead germanate single crystal

The results of measurement of the linear and nonlinear dielectric susceptibilities of pure and Ba-doped lead germanate, (Pb_{1? x} Ba _x )₅Ge₃O₁₁ with x = 0, 0.02 and 0.05, single crystals are presented. The change in the sign of the third-order dielectric susceptibility, χ ₃, as predicted by the thermodynamic theory of the continuous phase transitions, is observed in pure crystal. On the contrary, in the Ba-doped crystals, the third-order dielectric susceptibility is positive and shows a peak near the temperature, which corresponds to the position of the peak of the linear dielectric susceptibility, χ ₁. This result indicates that the Ba-doped lead germanate crystals do not show features typical of a continuous phase transition. In B-doped lead germanate crystal, the scaled nonlinear sucsebtibility, a ₃, shows ferroelectric relaxor-type behavior.     

Anomalous behavior of linear and nonlinear longitudinal susceptibilities below T c in a weakly anisotropic CdCr2Se4 ferromagnet

Frequency dependences of the linear and nonlinear longitudinal dynamic susceptibilities of an almost isotropic cubic CdCr₂Se₄ ferromagnet were studied experimentally in the ordered phase. It was found that at frequencies above the two-magnon creation threshold the linear susceptibility decreases as χ₁∝ω^?0.28 with increasing frequency and the nonlinear susceptibility decreases as χ_n∝ω^?0.73, irrespective of n, where n is an odd number. The observed susceptibility anomalies are due to the dipolar forces that violate the conservation of total spin.     

聚合物慢极化的唯象理论

将晶态相变中的唯象理论方法推广用于聚合物，说明了聚合物结构转变过程中的介电行为和空间电荷驻极体效应．晶态相变是一级结构的转变，联系着快极化介电常数ε_h的异常．聚合物的各种转变是二级和三级结构的转变，ε_h并无异常而出现慢极化介电常数倒数ε_l^-1的抛物型软化．理论与聚丙烯的实验结果很好地符合 关键词：     

Dielectric properties of (NH4)2SO4 crystals in the range of electronic excitations

Spectra of the real and imaginary parts of the pseudo‐dielectric permittivity, 〈?₁〉(E) and 〈?₂〉(E), of ferroelectric ammonium sulfate crystals, (NH₄)₂SO₄, have been measured in the range of electronic excitations 4.0 to 9.5 eV by ellipsometry using synchrotron radiation. Temperature dependences of the corresponding susceptibilities, 〈χ₁〉(T) and 〈χ₂〉(T), obtained for the photon energy E = 8.5 eV, related to excitations of oxygen p‐electrons, reveal sharp peak‐like temperature changes near the Curie point T_C = 223 K. The large temperature‐dependent increase of the imaginary part of the susceptibility χ₂(T), together with a simultaneous decrease of the real part of the susceptibility χ₁(T), take place at the phase transition. These anomalies have been ascribed mainly to the SO₄ group of the crystal structure.     

Measurement of third-order nonlinear susceptibilities by non-phase matched third-harmonic generation

The third-order susceptibilities χ _xxxx ⁽³⁾ (?ω₃;ω₁,ω₁,ω₁) of some liquids, solids and air are determined by third-harmonic generation. The samples are placed behind the focal region of a laser beam in an evacuated environment to avoid third-harmonic generation of the surroundings. For fluid media the sample cell is made out of two thin fused quartz plates and oriented to an angle of zero net third-harmonic production in each window (minimum Maker fringe position).     

Linear and nonlinear AC magnetic susceptibilities in intercalation compound FexTiS2

The harmonic, second and third higher harmonic components of the induced voltage of a sample coil under application of a low-field ac magnetic field, with and without static field, have been measured in the spin-glass, cluster-glass, and ferromagnetic phases of the intercalation compound Fe_xTiS₂ over the temperature range 1.5-300 K. Using a phenomenological expression for the magnetization, we have obtained independently the relative magnitudes of the linear and nonlinear ac magnetic susceptibilities χ₀, χ₁ and χ₂ for each magnetic phase.     

Second- and third-harmonic generations for a nondilute suspension of coated particles with radial dielectric anisotropy

We derive expressions for the effective nonlinear susceptibility tensors for both the second harmonic generation (SHG) and induced third harmonic generation (THG) of nonlinear composite materials, in which nondilute coated particles with radial dielectric anisotropy are randomly embedded in the linear host. Two types of coated particles are considered. The first is that the core possesses a second order nonlinear susceptibility and the shell is linear and radially anisotropic, while the second is that the core is linear with radial anisotropy and the shell has a second order nonlinear susceptibility. We observe greatly enhanced SHG and THG susceptibilities at several surface plasmon resonant frequencies. For the second model, due to the coating material being metallic, there exists two fundamental resonant frequencies ω_c1 and ω_c2, whose difference ω_c2-ω_c1 is strongly dependent on the interfacial parameter and the radial dielectric anisotropy. Furthermore, in both systems, the adjustment of the dielectric anisotropy results in larger enhancement of both SHG and induced THG susceptibilities at surface plasmon resonant frequencies than the corresponding isotropic systems. Therefore, both the core-shell structure and the dielectric anisotropy play important roles in determining the nonlinear enhancement and the surface resonant frequencies.     

Fluorescence and Nonlinear Optical Properties of Alizarin Red S in Solvents and Droplet

The enhancement of the nonlinear properties of materials is an interesting topic since it has many applications in optical devices and medicines. The Z-scan technique was used to study the values of the two-photon absorption (β), second-order molecular hyperpolarizability (γ_R), third-order susceptibility (χ_R), and nonlinear refractive index (n₂) of Alizarin Red S in different media using a continuous-wave diode-pump laser radiation at 532 nm. For Alizarin Red S in a droplet, the β, n₂, χ_R, and γ_R were estimated at the order of 10^?7 cm²/W and 10^?12 cm/W, 10^?3 m³ W^?1 s^?1 and 10^?24 m⁶ W^?1 s^?1, respectively. The results indicated that the values of β and n₂ reduced, whereas the values of χ_R and γ_R were enhanced when the solvent was changed from droplet to water, DMF, and dimethyl sulfoxide due to the change in the solvent’s dielectric constant (ε). Moreover, the values of β were enhanced by an increase in the concentration of the surfactant in the aqueous solution. The absorption spectra of Alizarin Red S in the aqueous solution was observed at 428 nm, and a few red shifts in the absorption spectra were observed with a reduction in the dielectric constant of the medium. The same effect was observed in the absorption spectra of Alizarin Red S in the droplet when the bulk dielectric constant reduced. The dielectric constant can affect the fluorescence spectra of Alizarin Red S when the solution is changed from water to dimethyl sulfoxide. The dipole moments of Alizarin Red S in the different media were studied using the quantum perturbation theory.     

Ferroelectric phase transition in Cs3Bi2I9

Single crystals of Cs₃Bi₂I₉ have been grown. Polarized-optical, dielectric, and calorimetric studies have been performed, along with measurements of birefringence, and the coefficients of elasticity c ₄₄, and linear expansion a over a wide temperature range. It is found that an intrinsic (pseudo-intrinsic) second-order phase transition to the ferroelastic phase takes place at T ₀=220.0±0.6 K accompanied by a change of the crystal symmetry from 6/mmc to 2/m. The transition parameter depends linearly on the shear strain x ₅ and varies with temperature according to a power law with exponent β=0.5. Zh. éksp. Teor. Fiz. 39, 1850–1852 (October 1997)     

LARGE AND EXTREMELY FAST THIRD-ORDER NON-LINEARITY OF Ag NANOPARTICLES EMBEDDED INTO A CsxO SEMICONDUCTOR MATRIX

The third-order optical nonlinearity of Ag-O-Cs thin films, where Ag nanoparticles are embedded into a Cs_xO semiconductor matrix, was measured by the femtosecond optical Kerr technique. The third-order nonlinear optical susceptibility, χ⁽³⁾, of the thin films was estimated to be 1.1×10^-9 esu at the incident wavelength of 820 nm. The response time, i.e. the full width at half-maximum of the Kerr signal, is as fast as 114 fs only. The intrinsic third-order optical nonlinearity can be attributed to the intraband transition of electrons from the occupied state near the Fermi level to the unoccupied state. It is suggested that such a nonlinearity is further enhanced by the local field effect that is present in the metallic nanoparticles composite thin films.     

Characteristics of degenerated four wave mixing in ZnS/CdSe/ZnS quantum dot quantum well with multi-shell structure

The wave functions and eigenenergies of electrons in ZnS/CdSe/ZnS cylindrical quantum dot quantum well (QDQW) have been calculated by solving a three-dimensional nonlinear Schrödinger equation, in the framework of the effective-mass envelope-function theory. The third-order susceptibilities of the degenerated four waves mixing (DFWM) have been calculated theoretically by means of compact density matrix. The third-order susceptibilities as the function of the shell radius R₂, R₃ have been analyzed. The results show that the magnitude of nonlinear susceptibility is increased with the increasing of well radius. The resonance frequency of the photon have a shift when R₂ or R₃ is increasing and the relation between nonlinear susceptibility and relaxation time has also been studied.     

The potts glass in uniform and random fields: a monte carlo investigation

As a simple model of an anisotropic orientational glass with short range forces, the 3-state Potts model on the simple cubic lattice with nearest neighbor interactions drawn from a Gaussian distribution is considered. With Monte Carlo methods we study the response of the system to a uniform “field” which favors one of the states. This is motivated by experiments which apply stress that favors one molecular orientation of the quadrupolar glass. The responsem to that fieldh=H/k _BT is analyzed in terms of an expansionm= χ₁ h+χ₁ h ²+χ₁ h ³+..., where χ₁ is the linear susceptibility, and χ₂,χ₁₃ are nonlinear susceptibilities. Unlike the case of spin glasses, where the spin inversion symmetry of the system in the absence of fields implies χ₂≡0,χ₂ is nonzero here and diverges to ?∞ at the zero temperature transition of the model, while χ₃ diverges to +∞ as in spin glasses. At inifinite temperature, however, χ₁=1/3, χ₂=1/18 and χ₃=-1/54, i.e. the nonlinear susceptibilities have a different sign as at low temperature. In contrast, a random field does not induce a uniform order parameterm but only a glass order parameterq. The temperature dependence of this glass order parameterq(T) shows for intermediate field strength order parameterq(T) shows for intermediate field strength a maximum of the slopedq(T)/dT very similar to corresponding experiments.     

Crystal field and quadrupole interaction effects in YbXO4 Zircons (X = V, P)

The magnetic and magnetoelastic properties of YbPO₄ and YbVO₄ crystals are investigated experimentally and theoretically; the crystal field parameters are determined, as well as the magnetoelastic coefficients B ^μ and total quadrupole coupling constants G ^μ for all symmetry modes. It is found that, for H ∥ [100], γ-symmetric quadrupole interactions predominate and are responsible for a significant contribution to the third-order susceptibility, magnetization, magnetostriction, and elastic constant. It is demonstrated that, in the absence of an external field, these interactions do not lead to quadrupole ordering, because the respective deformation susceptibility χ_γ is several times less than the critical value of 1/G ^γ. The influence of an external magnetic field along different symmetry axes on the quadrupole effects and quadrupole interactions in Yb zircons is investigated. It is demonstrated that, for H ∥ [110], the susceptibility χ_γ increases with the field, so that in a fairly strong field in the investigated crystals one can expect a γ-symmetric stimulated phase transition.     

Role of annealing on morphological,linear and nonlinear properties of nanoparticle of Tris [2-phenylpyridinato-C2, N] Iridium III films prepared by electron beam evaporator

Tris(2-phenylpyridinato-C₂, N] Iridium III, Ir(ppy)₃, is experimentally investigated as a novel deposited thin film. Ir(ppy)₃ thin films were fabricated by the electron beam evaporator technique. X-ray diffraction (XRD) of Ir(ppy)₃ powder is investigated to be polycrystalline with triclinic crystal. XRD pattern of Ir(ppy)₃ film and the annealed film is analyzed, and the average of crystallite size slightly increases with thermal annealing from 14 to 40 nm. The linear optical parameters were estimated and found that the annealing effect on lattice dielectric constants, dispersion energy, oscillator energy, and the ratio of carrier concentration to its effective mass. The Urbach energy and optical energy gap are estimated at different thermal annealing. On the other hand, dielectric constants and optical conductivity were estimated and found that the annealing plays a remarkable role in the increasing of their values. The calculated values of third-order susceptibility were increased by thermal annealing. Thus, the thermal annealing can be utilized as a tool to modify the optical properties of Ir(ppy)₃ films, which can be used in many important applications such as high capacity communication network.     

Ferri-para-magnetism of tungsten and its carbide cermets for elevated temperature sensor application

In routinely analyzing experimental results of low-temperature, 5?K?≤?T?≤?300?K, magnetic susceptibility χ(T) of fused tungsten and its fused carbide cermets, hereafter called “the materials”, by assuming the susceptibility satisfying the Néel ferrimagnetic formula, χ^?1?=?χ₀^?1?+?χ₁^?1?+?χ₂^?1, where χ₀^?1, χ₁^?1, and χ₂^?1 are respectively the inverses of the Pauli paramagnetic, χ₀?>?0, a Curie diamagnetic, χ₁?=?C/T < 0, and a lattice diamagnetic susceptibilities, χ₂?=?(–1/b)(T ? Θ_p)<?0, this study finds that the increase in susceptibility of the materials is principally due to the effect of the Curie diamagnetic term in the formula and might be caused by the demagnetizing field that is induced by the interstitial vacancy in, e.g., tungsten lattice. By extending the formula to the region of lower (<5?K) and higher (>300?K) temperatures, one finds two singular points in the susceptibility inverse curve χ^?1. One is at Θ_p?<?0, and the other Θ_a?=??C/χ₀?>>?0, e.g., Θ_p?=??1.73?K, and Θ_a?=??C/χ₀?=?+8655?K for tungsten. In view of their susceptibility precisely satisfying the Néel ferrimagnetic formula in the temperature range of 5?K and 300?K, they are called “ferri-para-magnetism” and are good for elevated temperature sensor application if the temperature extension is satisfied. As temperature exceeding an asymptotic temperature, Θ_a, the paramagnetic state turns to a diamagnetic state, suggesting that there might be a superconducting transition at this temperature for some of the materials with Θ_as that are lower than their melting points, e.g., Θ_a(C7M1)?=?+2735?K and Θ_a(-VC)?=?+2242?K.     

Lattice mediated interactions and ferroelectric anomalies in the crystal (CH3NH3)5Bi2Cl11 (PMACB)

Abstract

A two-sublattice compressible pseudospin model has been constructed to describe the behaviour of the spontaneous polarisation of PMACB in the temperature region comprising the ferroelectric phase transition (T=307K) and the isomorphous anomaly (T= 180 K). A strong coupling of pseudospins with a “pancake” strain ?(2ε₃₃ ? ε₁₁ - ε₂₂) /3 resulting from the comparison of the model with the experimental spontaneous polarisation agrees with the existing data on the dielectric susceptibility, and on the specific heat. The ferroelectric phase transition then turns out to be close to a tricritical point. The numerical values of the parameters of the model show how the ferroelastic phase transition (T=260K) can occur in this crystal without any discernible effect on the specific heat and on the dielectric susceptibility.     

Temperature and pressure dependences of the properties and phase transition in paratellurite (TeO2: Ultrasonic,dielectric and Raman and Brillouin scattering results

The effects of temperature and pressure on the ultrasonic propagation properties, dielectric constants and the Raman and Brillouin spectra in paratellurite (TeO₂) were investigated with emphasis on the behavior in the vicinity of the newly-discovered, pressure-induced phase transition. The transition is found to be second-order and purely strain-induced, driven by a soft shear acoustic mode propagating along a <110〉 and polarized along a (110) crystal direction. Such pure-strain transitions were previously discussed by Anderson and Blount and the transition in paratellurite is the first observation of this kind of transition. No evidence was found for any coupling of the soft mode to any other acoustic or optic mode, although small anomalies associated with lattice strains accompanying the transition were observed in some of the elastic and dielectric constants. Analysis of the effective elastic constant C, governing the soft mode velocity indicates that, within experimental uncertainty, the transition can be described by mean-field theory. Although the apparent attenuation of the soft mode increased significantly near the transition, it is concluded that this effect is probably due to the fact that the phase and group velocities are not parallel rather than to intrinsic dissipative processes in the crystal. With the exception of C₄₄, the remaining elastic constants and Raman-active phonon frequencies displayed normal increases with pressure. No soft Raman-active modes were observed in either phase. The static dielectric constants ?₁ are large, due to the large electronic polarizability of TeO₂, and the anisotropy in ? results almost entirely from the anisotropy in the optical dielectric constants ?_∞. In the low pressure tetragonal phase both ?_a and ?_c exhibit normal temperature dependences and ?_c decreases with pressure; however, ?_a exhibits an anomalous increase with pressure. Temperature, pressure and uniaxial stress measurements are combined to evaluate the various contributions to the temperature and pressure dependences of ?. Combining the ? data with available i.r. measurements demonstrated that the generalized Lyddane-Sachs-Teller relation is well obeyed for TeO₂. Finally, the Szigetti effective charge ratios were determined for the lowest frequency IR-active modes. These ratios were found to be quite low, being 0.27 and 0.18 for the a-axis responses, respectively, indicating that the bonding is highly covalent.     

杂质对K2ZnCl4晶体无公度结构相变的影响

对K₂ZnCl₄铁电晶体在无公度-公度转变的相变点附近的孤子行为进行了研究。发现在相变点附近杂质使介电函数明显偏离居里-外斯定律,并导致介电峰值的明显下降;同时还发现杂质对升温相变点T_c^h较之对降温相变点T_c^c有更大的影响,这与Rb₂ZnCl₄等晶体中的情况恰好相反。采用朗道自由能理论可较好地描述杂质在相变点附近对介电函数的影响。分 关键词：     

Nonlinear susceptibilities of vapors and solutions of organic dyes

Results of theoretical studies of laser and Kerr nonlinear susceptibilities of vapors and solutions of organic dyes using a series of polycyclic arenes as an example are presented. Nonlinear susceptibilities of the third χ⁽³⁾ (?3ω; ω, ω, ω) and the fifth χ⁽⁵⁾ (?3ω; ω, ω, ω, ω, ?ω) orders of a series of organic dyes responsible for third harmonic generation of Nd:YAG laser radiation are calculated within the context of the free electron model. Results of calculations of their Kerr third-order nonlinear susceptibilities χ⁽³⁾ (?ω; ω, ?ω, ω) and non-linear refractive indices n ₂ are presented. The calculation results are compared with experimental data on third harmonic generation in naphthalene vapors and with χ⁽³⁾ (?ω; ω, ?ω, ω) as well as n ₂ of paraterphenyl and naphthalene solutions.     

Anomalies of transverse dielectric susceptibility in DyVO4 and DyAsO4 Jahn-Teller crystals,caused by quadratic vibronic coupling

The transverse dielectric susceptibility χ_⊥ in DyVO₄ and DyAsO₄ crystals is examined theoretically. The terms of quadratic vibronic coupling, which contain as the optical E_u modes so the soft acoustic branch or the electron order parameter, are taken into account. Such coupling is shown to lead to anomaly of χ_⊥ near the temperature of Jahn-Teller structural phase transition. From the experimental data the constants of the quadratic vibronic coupling are appreciated.