International Journal of Modern Physics B

In this paper, a brief review on reversible dielectric nonlinearity (RDN) was presented and the mechanism of tunability for ferroelectric ceramics was discussed in several different scale levels, such as atomic level (intrinsic nonlinearity described by ferroelectric thermodynamic theory), nano-meter scale (polar nano-region response), submicron scale (ferroelectric domain and domain wall motion), micron scale (polycrystalline structure of ceramics and surface layer) and macroscopic scale (field induced phase transition). It suggests that RDN is a multi-scale phenomenon and is temperature and frequency-sensitive. The halving field E₀ in Roberts' Equation may be a good attempt for the quantitating of RDN. The stability of RDN in paraelectric phase is also mentioned.

We have studied the influence of the new chiral non-mesogenic seco-estrone derivatives 1-7, synthesized in several synthetic steps starting from estrone, onto the physical characteristics of the binary mixtures of cholesteric liquid crystals. We have examined the phase transitions of the mixture of cholesteryl laurate and cholesteryl enantate with the added chiral non-mesogenic additives 1-7 (45%-45%-10%; Mix.1-Mix.7, respectively). A considerable shift of the I→Ch phase transition temperature, as well as of the temperature of the SmA* phase formation, was observed. X-ray diffraction data enabled the determination of the molecular structures of the compounds 3, 5, 6 and 7, the crystal lattice parameters of the new chiral additives and their molecular length (ℓ) and width (d*), as well as some parameters of the mixtures Mix.1-Mix.6: the thickness of smectic layers and the longitudinal spacing distance in the cholesteric phase (d) and the average distance between the long axes of neighbouring molecules (D). Using molecular-mechanic calculations, on the basis of solved molecular structures, the most probably conformation of the other compounds (1, 2 and 4) used in this work is determined. We have also investigated the influence of these chiral additives onto the pitch of the cholesteric helix of a binary mixture of cholesteric liquid crystals.

The electron mobility conditioned by confined and interface polar-optical phonons for a quasi-one-dimensional cylindrical quantum wire embedded in a dielectric medium is investigated analytically. It is shown that the inclusion of the polar optical phonon confinement effects is crucial for accurate calculation of the low-field electron mobility in quantum wire. Taking into account the inelasticity of the electron-polar optical phonon interaction, the electron mobility is derived by a method which was successfully applied in three- and quasi-two-dimensional cases. The contribution of intersubband transitions to electron mobility for the Cd_0.35Zn_0.65Se quantum wire embedded in the CdZn dielectric medium is estimated. The extremums on the mobility dependences on wire radius and Cd concentration are obtained.

We simulate numerically the dynamic properties of new soliton with quasi-coherent two quanta in the improved model by fourth-order Runge–Kutta way. We observed that the window of formation of new soliton is shifted toward smaller values of coupling constants when compared with the Davydov's soliton with one quantum and Förner's soliton with two quantum model. The new soliton formation starts at (χ₁+χ₂)=20 PN, and pinning starts from (χ₁+χ₂)=86 PN. The pinned solitons are also observed if both quanta are on the same end of the chain in the initial state. The behaviors of new soliton are varied under influences for variations of characteristic parameters arising from the structure nonuniformity of protein molecules. Although the new soliton is also sensitive to the dipole-dipole interaction and diagonal disorder, the sensitivity to the impurity is weaker than that of the Davydov's and Förner's solitons. Therefore, the new soliton is robust against the fluctuations of coupled constant, dipole-dipole interaction and diagonal disorder arising from the impurity or structure nonuniformity, when compared with that of the Davydov's and Förner's solitons.

Polaronic shifts of the donor binding energies in an electric field in a quantum well are presented here. The properties of a polaron in a quantum well are investigated within the second-order perturbation theory. GaAs/Ga_1-xAl_xAs quantum well is chosen as an example to calculate the polaron energy. Since this system is a weak polar material, the electron-lattice coupling constant is small so this effect is considered by second-order perturbation theory. The polaronic effects are suppressed when an electric field is coupled. The diamagnetic susceptibility is also calculated and the results are compared with the results obtained using other approximation methods.

The Kardar–Parizi–Zhang equation for surface growth has been analyzed in the regime where the nonlinear coupling constant, λ, is small (Edwards–Wilkinson equation). By using the Fourier transformation the finite size corrections on the mean-square width could be calculated. It is found that the calculated interface width for behaves as and for behaves like .

The purpose of this research is to investigate the structure of lead zirconate titanate ceramics (Zr:Ti=52:48) when doped with Pr₂O₃ and the corresponding properties such as micro-structural properties, physical properties, dielectric constant (ε_r), piezoelectric properties (k_p, Q_m, and d₃₃), and the ferroelectric property. The materials were prepared via conventional mixed oxide method and sintered at 1200°C. The Rietveld refinement of X-ray diffraction patterns and combination of both patterns revealed the tetragonal structure for all samples to have space group of P4mm. For higher dopant content (10 mol%), the pyrochlore phase of Pr₂O₃ also appeared in the respective samples. These pyrochlore phases caused the detriment of dielectric and piezoelectric properties. For those with lower dopant content (1.00 mol%), the Pr ion substituted at the A and B sites with isovalent dopant effects, i.e. a lower value of ε_r, and k_p. The hysteresis loops indicated the ferroelectric property for all samples. The microstructure showed dense grain according to a high density and the additional phases of Pr₂O₃ were clearly observed for 10 mol% doping. The Curie temperature decreased with increasing dopant content, as determined from high temperature X-ray diffraction and differential scanning calorimetry.

Materials with batch formula Pb_(1-x-3y/2)R_yBa_xNb₂O₆, where R=Y, (1-x)=0.73, 0.63, 0.53 and y=0.00, 0.02 have been prepared by the double sintering method. Substitution of yttrium (Y) restored tetragonal symmetry of PBN but reduced lattice parameters, cell volume and enhanced the density. Transition temperature of PBN has decreased due to the substitution of Y³⁺. Enhanced room temperature spontaneous polarization (P_s)=149.97 μC/sq. cm has been observed in PBN53, which is above MPB, whereas enhanced value of P_s=112.74 μC/sq. cm is found in Y: PBN63 at MPB region. The room temperature Pyroelectric coefficient (P_RT=1.07) has been observed in the composition where maximum volume of P_s is obtained. Similarly, enhanced values of piezoelectric coefficients K_p=0.244, K_t=0.353, K₃₁=0.131, d₃₁=60, d₃₃=159 and g₃₁=3.65 have also been found in the same material PBN53. Substitution of Yttrium enhanced the stiffness constant 13.59 in PBN 73 to 14.27 of Y: PBN73.

Critical temperature of layered superconductors is studied using anisotropic Eliashberg theory in intermediate e-ph coupling. The results are shown to be in qualitative agreement with experimental data for the superconducting magnesium diboride MgB₂.

We study density of states in the symmetrical and asymmetrical two-band periodic Anderson models at various band fillings with self-consistent calculation of the orbital occupancies. The application of the improved truncation approximation for irreducible Green functions that takes into account resonance broadening and band shifting inter-orbital exchange effects, resulted in the appearance of four spectral density moments and four- or five-subbands in the density of states depending upon the parameters of the model. It is shown that closing of the hybridization gap can occur as the result of doping, applied pressure, or change of the f-band width.