Densificación de cerámicas de PZN-10PT a partir de polvos sintetizados por el método de reacción por combustión

((1-x)Pb(Zn1=3Nb2=3)O3-xPbTiO3-PZN-xPT) single crystals with perovskite structure near to the morphotropic phase boundary (MPB), x_0; 09, exhibit unusual large dielectric and piezoelectric constants. Preparation of PZN-PT ceramics with composition near to((1-x) Pb (Zn1 = 3Nb2 = 3) O3-xPbTiO3-PZN-xPT) monocristales con estructura de perovskita cerca del límite de la fase morfotrópica (MPB), x_0; 09, exhiben grandes constantes dieléctricas y piezoeléctricas inusuales. La preparación de cerámica PZN-PT con

Magnetic-field and confinement effects on the effective Landé g factor in Al xGa 1-x As parabolic quantum wells

The magnetic-field and confinement effects on the Land, factor in AlxGa1-xAs parabolic quantum wells under magnetic fields applied parallel or perpendicular to the growth direction are theoretically studied. Calculations are performed in the limit of low temperatures and low electron density in the heterostructure. The g factor is obtained by taking into account the effects of non-parabolicity and anisotropy of the conduction band through the 2 x 2 Ogg-McCombe Hamiltonian, and by including the cubic Dresselhaus spin-orbit term. A simple formula describing the magnetic-field dependence of the effective Land, factor is analytically derived by using the Rayleigh-Schrodinger perturbation theory, and it is found in good agreement with previous experimental studies devoted to understand the behavior of the g factor, as a function of an applied magnetic field, in semiconductor heterostructures. Present numerical results for the effective Land, factor are shown as functions of the quantum-well parameters and magnetic-field strength, and compared with available experimental measurements

Nature of the magnetoelectric coupling in multiferroic Pb(Fe(1/2)Nb(1/2))O(3) ceramics

In this work, electrical permittivity measurements in lead iron niobate (PFN) ceramics were performed in the frequency and temperature ranges from 10 kHz to 1.2 GHz and from 15 to 450 K, respectively. the microwave dielectric results characterized unambiguously the magnetoelectric effect in PFN and demonstrated that the nature of such coupling arises indirectly via ferroelastic contribution rather than a direct coupling between electrical and magnetic order parameters. Moreover, it was also verified that such coupling can be enhanced or suppressed depending on the relative orientation between the probing electric field and the macroscopic ferroelectric polarization.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Fed Sao Carlos, Dept Fis, Grp Ceram Ferroeletricas, BR-13565970 Sao Carlos, SP, BrazilDepartamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, CEP 13251-900 Diadema, São Paulo, BrazilWeb of Scienc

Donor-impurity related binding energy and photoinization cross-section in quantum dots: electric and magnetic fields and hydrostatic pressure effects

We have studied the behavior of the binding energy and photoionization cross-section of a donor-impurity in cylindrical-shape GaAs-Ga0.7Al0.3As quantum dots, under the effects of hydrostatic pressure and in-growth direction applied electric and magnetic fields. We have used the variational method under the effective mass and parabolic band approximations. Parallel and perpendicular polarizations of the incident radiation and several values of the quantum dot geometry have also been considered. Our results show that the photoionization cross-section growths as the hydrostatic pressure is increased. For parallel polarization of the incident radiation, the photoionization cross-section decreases when the impurity is shifted from the center of the dot. In the case of perpendicular polarization of the incident radiation, the photoionization cross-section increases when the impurity is shifted in the radial direction of the dot. For on-axis impurities the transitions between the ground state of the impurity and the ground state of the quantum dot are forbidden. In the low pressure regime (less than 13.5 kbar) the impurity binding energy growths linearly with pressure, and in the high pressure regime (higher than 13.5 kbar) the binding energy growths up to a maximum and then decreases. Additionally, we have found that the applied electric and magnetic fields may favor the increase or decrease in binding energy, depending on the impurity position