J. A. Eiras

Effects of the postannealing atmosphere on the dielectric properties of (Ba, Sr)TiO3 capacitors: Evidence of an interfacial space charge layer

The dielectric properties of ~Ba, Sr!TiO 3 films were found to be remarkably sensitive to the postannealing treatment atmosphere. This study demonstrates that postannealing in an oxygen atmosphere increases the dielectric relaxation phenomenon and that postannealing in a nitrogen atmosphere produces a slight dielectric relaxation. Such dependence of the dielectric relaxation was related both to oxygen vacancies and to the presence of negatively charged oxygen, trapped at the grain boundary and/or at the electrode/dielectric film interface.

90° domain wall relaxation and frequency dependence of the coercive field in the ferroelectric switching process

The mechanisms involved in the polarization switching process in soft and hard Pb(Zr53,Ti47)O3 (PZT) bulk ceramics were investigated through the dependency of the hysteresis loop on the frequency. In order to determine the influence of the defects on the domain switching dynamics, the samples were characterized in the virgin state and after a fatigue or a depinning process. The frequency dependence of the polarization revealed a strong relaxation of the 90° domain walls at ∼100 Hz. The results also revealed a strong influence of the kind of defect and their distribution in the ferroelectric matrix on the domain switching dynamics, which were reflected in the frequency dependence of the coercive field and the percentage of the backswitching. Initially, it was observed that the frequency dependence of the coercive field for the soft and the hard PZT in the virgin state had just one rate of change per decade in the entire frequency range investigated, which is the standard behavior found in the literature. H...

Structural and spectroscopic properties of rare-earth (Nd3+,Er3+, and Yb3+) doped transparent lead lanthanum zirconate titanate ceramics

This work presents the structural and spectroscopic characterization of transparent lead lanthanum zirconate titanate ceramics doped with Nd3+, Er3+, or Yb3+ ions. High optical quality samples presenting the perovskite structure were prepared through a mixed oxides method followed by conventional sintering or uniaxial hot pressing. Absorption and luminescence spectra were measured, and radiative emission parameters were calculated for Nd3+- and Er3+-doped samples. The results indicate the potential of these polycrystalline host–ion combinations for the construction of diode-pumped lasers in the near-infrared region.

Phase transition at low temperature in NaNbO3 ceramic

The electric permittivity of the sodium niobate ceramic was investigated in the temperature range from 15 up to 900 K, at frequencies from 100 Hz to 1 MHz. Three anomalies were found in the permittivity curve. A phase transition for NaNbO3 was assigned to anomaly at around 280 K, while other two ones have previously been reported. In addition, the dielectric permittivity dependence with the temperature and frequency, at temperatures lower than 400 K, showed two regions with typical characteristics of a relaxor ferroelectric materials.

Raman study of morphotropic phase boundary in PbZr 1 − x Ti x O 3 at low temperatures

The Raman spectra of

Evaluation of domain wall motion in lead zirconate titanate ceramics by nonlinear response measurements

{\mathrm{PbZr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}

90° domain reorientation and domain wall rearrangement in lead zirconate titanate ceramics characterized by transient current and hysteresis loop measurements

ceramics with titanium concentration varying between

2.8 and 1.55μm emission from diode-pumped Er3+-doped and Yb3+ co-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic

x=0.40

Monoclinic phase ofPbZr0.52Ti0.48O3ceramics: Raman and phenomenological thermodynamic studies

and 0.60 were measured at 7 K. By observing the concentration-frequency dependence of the vibrational modes, we identified the boundaries among the rhombohedral, monoclinic, and tetragonal ferroelectric phases. The analysis of the spectra was made in the view of group theory analysis making possible the assignment of some modes for the monoclinic phase.

Short-range disorder in lanthanum-doped lead titanate ceramics probed by Raman scattering

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 wal...