Search

A technique for the simultaneous measurement of the detuning and the linewidth of the source emitter on the microcavity light-emitting diode (MCLED) was described. The method used numerical simulations and a fitting procedure with the angular emission pattern measured on the MCLED. It was shown that the efficiency of a MCLED is directly related to its detuning. The efficiency was peaked at an optimum detuning and decreased rapidly from this value.

Dielectric and direct piezoelectric responses in non-doped and Mn-doped Pb0.91La0.09(Zr0.65,Ti0.35)O3 ceramics are experimentally studied. The permittivity and the direct piezoelectric coefficient were measured by applying an ac electric field or a mechanical stress, respectively. The results show that the dielectric response is mainly due to an extrinsic contribution at room temperature. A notable reduction in room temperature dielectric losses by Mn-doping is verified. The temperature of the minimum of the losses depends on the Mn-content, enabling the Pb0.91La0.09(Zr0.65,Ti0.35)O3 properties to be tuned from soft to hard. A significant stabilization of the dielectric and piezoelectric responses, related to domain wall motion reduction, is confirmed in Mn-doped materials, so these materials become good candidates for transducer applications. The correlation between the dielectric constant and dielectric losses is discussed in terms of the Rayleigh model. Results show that Mn-doped PLZT response does not fit this model. This fact could be explained by taking into account the nature of the defects created by manganese addition. These complex defects act as pinning centers, and the reversible movement of domain walls provide a significant contribution to the response of these materials. [ABSTRACT FROM AUTHOR]

Nonlinear response of pure and doped Pb(Zr1-xTix)O3 ceramics, with different compositions, has been analyzed in order to evaluate the domain wall motion in these materials. The study of dielectric and converse piezoelectric response shows a clear dependence of the domain wall mobility on the ferroelectric phase. Large lattice distortion in tetragonal samples produces a low mobility of the ferroelectric-ferroelastic domain walls. The influence of the type of defects on the nonlinear response has been explored. The results show that the relative increase of the domain walls mobility in donor-doped materials is greater than the decrease in acceptor-doped materials due to the pinning produced by complex defects. Rayleigh law has been used to evaluate the irreversible contribution of the domain walls movement to the nonlinear dielectric response. The analysis reveals that in presence of oxygen vacancies, the dielectric response cannot be attributed exclusively to the contribution of the irreversible domain wall motion. Furthermore, dielectric constant perpendicular to poling direction has been measured in rhombohedral donor-doped and acceptor-doped samples. The nonlinear response in the perpendicular direction is higher than in the poling direction, and this effect can be enlarged by the presence of complex defects. Dielectric nonlinear response has also been measured at different frequencies in rhombohedral donor-doped sample. A logarithmic dependence on frequency has been observed, which can be explained by the pinning effect on the ferroelectric domain walls by randomly distributed defects. [ABSTRACT FROM AUTHOR]