Carlos Alemany

Effect of PMN modification on structure and electrical response of xPMN–(1−x)PZT ceramic systems

The structural and electrical properties of xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr,Ti)O3 ternary ceramic system with the composition near to the morphotropic phase boundary (MPB) and of xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr0.47Ti0.53)O3 ceramics were investigated as a function of the Pb(Mg1/3Nb2/3)O3 (PMN) content by scanning electron microscopy (SEM), X-ray diffraction (XRD), dielectric and piezoelectric spectroscopy and polarization-electric field measurement technique. Studies were performed on the samples prepared by a columbite precursor method for x=0.125, 0.25 and 0.5. Room temperature SEM investigations revealed common trends in the grain structure with increasing PMN content. XRD analysis demonstrated that with increasing PMN content in xPb(Mg1/3Nb2/3)O3–(1−x)Pb(Zr0.47Ti0.53)O3, the structural change occurred from the tetragonal to the pseudocubic phase at room temperature. Changes in the dielectric and ferroelectric behavior were then related to these structural trends and further correlated with the piezoelectric properties. The results of ferroelectric hysteresis measurements, in conjunction with dielectric spectroscopy, demonstrated an intermediate, relaxor-like behavior between normal and relaxor ferroelectrics in the solid solution system, depending on the PMN content.

Dielectric properties and phase transition behavior of xPMN-(1 - x)PZT ceramic systems

The dielectric properties and phase transition behavior of the pseudo-ternary xPb(Mg1/3Nb2/3)O3-(1 − x)Pb(Zr,Ti)O3 solid solution system were investigated as a function of the Pb(Mg1/3Nb2/3)O3 (PMN) content and Ti/Zr ratio for selected compositions. The investigations have demonstrated a general trend in broadening of the phase transition and increasing diffusivity with increasing PMN content. For the morphotropic phase boundary (MPB) compositions, the dielectric permittivity maximum, its temperature (Tm) and the Curie-Weiss constant were found to decrease with increasing Mg1/3Nb2/3 concentration. When a Ti/Zr ratio was constant and equal to 53/47, temperature-dependent investigations demonstrated that the dielectric parameters involved in a modified Curie-Weiss law increase monotonically with increasing PMN content and Tm moves toward room temperature with average rate of ≈ −4.1°C/mol% as well. A phase transition in 0.5PMN-0.5Pb(Zr0.47Ti0.53)O3 and 0.25PMN-0.75Pb(Zr0.60Ti0.40)O3 ceramic systems exhibited a diffused behavior with a characteristic frequency dependence of Tm. From pyroelectric measurement, an unusual spontaneous polarization behavior at about 215 K is reported for some MPB compositions.

Temperature dependence of piezoelectric, elastic and dielectric coefficients at radial resonance of piezoceramics with an Aurivillius-type structure

Aurivillius-type structure compounds are considered good candidates for piezoelectric materials at high temperature, due to their high ferro-paraelectric phase transition temperature. Despite this fact, very few papers have been published on the study of piezoelectric properties at the expected working temperatures. An iterative automatic method has been used in this work to characterize the piezoelectric, electromechanical, and elastic properties at radial resonance of thin ceramic disks with composition (SrBi/sub 2/Nb/sub 2/O/sub 9/)/sub 0.35/(Bi/sub 3/TiNbO/sub 9/)/sub 0.65/[SBN/BTN 35/65], from room temperature up to the ferro-paraelectric phase transition. Ceramics were prepared by sintering or by recrystallization after hot-pressing of mechanically activated precursors. By this new method, ceramics with controlled texture and microstructure are obtained. The influence of the processing route in the properties of the ceramics, over the whole temperature range of piezoelectric activity, is discussed. Values of d/sub 31/=2.1 pC/N and k/sub p/=2.9% at 500/spl deg/C are achieved.

Ferropiezoelectricity of calcium modified lead titanate ceramics

When a ceramic with grain Boundaries rich in OPb is poled Beyond 4O kV cm−1 at ferroelectric phase, the highest anisotropy of electromechanical coupling factor is obtained. An attempt to explain this Behaviour is made in terms of domain switching and the strains and cracks generated during cooling down poling. Apart from composition, two more factors are revealed as contributing to the disappearance of radial coupling in Ca-modified lead titanate ceramics: microtexture and electric poling strategy.

Ageing of (Pb, La)(Zr, Ti)O3 ferroelectric ceramics and the space charge arising on hot poling

Polarization-temperature diagrams of pyroelectric charge and the decrease of remanent polarization (PR) at constant temperature are investigated in PLZT 8/65/35 ceramic samples. The arousal of space charge is shown to be unlike that of pyroelectric charge and highly dependent on poling temperature. This charge, measured by the thermally stimulated current in hot poled samples, obeys the dielectric discharge lawi=kt−n and is also responsible for the recovery ofPR after the samples have been thermically depoled in part, in contrast with samples poled at room temperature. The evolution ofPR follows the lawi =kt-n Int where the slopeB decreases with poling temperature when the sign ofPR is that of the former polarization. The ageing behaviour is correlated with the space charge that arises on hot poling.

Determination of the exponent

Abstract Due to the experimental indetermination of the temperature Tmax (e′max) because of the large broadening of the e′ (T) maximum in ferroelectric ceramics, we have carried through computer programs by taking values of Tmax in a ± 4°C interval of the experimental curves in order to get the best agreement for their paraelectric phase with the well known expression 1/e′ = 1/e′max + A(T-Tmax)

Poling strategy of PLZT ceramics

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