N. Cereceda

Dielectric characterization of the phase transitions in Pb1-y/2(Zr1-xTix)1-yNbyO3(0.03≤x≤0.04, 0.02≤y≤0.05)

The Curie temperature and the ideal thermal hysteresis of Pb1−y/2(Zr1−xTix)1−yNbyO3 (0.03 ⩽x⩽0.04, 0.02⩽y⩽0.05) ferroelectric ceramics have been investigated as a function of composition at the FRH–PC phase transition. Experimental results are analyzed using the generalized effective field approach and taking into account the composition dependence of the dimensionless parameters g and h corresponding to the second and third terms in the generalized effective field expansion. With this approach we can describe reasonably well the composition dependence of TC(x,y) at the FRH–PC transition and thermal hysteresis ΔT(x,y) in the narrow range of compositions investigated. The effects of the oxygen octahedra tilt in the dielectric constant at the FRL–FRH transition have also been investigated as a function of composition.

Investigation of the character of the phase transitions in Nb doped Zr-rich PZT by pyroelectric and dielectric measurements

We present a study of the character of the phase transitions of the solid solution PbZr1ˇxTixO3. Using the spontaneous polarization curves we determined the mean-field parameters. These parameters show the first order character of the phase transitions for the richer Zr content and its evolution with composition. The FRL‐FRH phase transition presents also first order character for high contents of Zr. The study of the thermal hysteresis, and the jump of the spontaneous polarization, allowed us to investigate this phase transition with composition. # 1999 Elsevier Science Limited. All rights reserved

O3 tilt and the Pb/(Zr/Ti) displacement order parameters in Zr-rich PbZr1-xTixO3 from 20 to 500 K

Neutron diffraction and dielectric data have been collected from a polycrystalline sample of PbZr1-xTixO3 (x=0.035) to determine the temperature dependence of the two-order parameters associated with the oxygen octahedral tilt and the Pb/(Zr/Ti) displacement, respectively, through the sequence of phase transitions FRL-FRH-PC present in this mixed system. The weak coupling between tilt and polarization (displacements) is satisfactorily described within the framework of a two-order-parameters statistical theory in which the respective effective fields involve two higher-order terms in addition to a linear term.

Energy conversion with Zr-rich lead zirconate/titanate ceramics

The conversion efficiency and power output to convert thermal energy to electrical energy by means of a ferroelectric–ferroelectric phase transition has been investigated. The material used was the ceramic mixed system lead zirconate/titanate (PZT) with a very Zr-enriched composition (Zr/Ti=97/3%). We have studied the performance dependence on sample thickness and working frequency, the main relevant parameters for a given PZT composition. The observed optimum values of efficiency and power output are analyzed in terms of the two main characteristic relaxation times of the process, the thermal time (sample thickness dependent) and the electric time (thickness independent). Possible ways of improving the overall performance are discussed.

Neutron difraction investigation of the FRL−FRH transition in Nb doped PbZr1−xTIxO3 with x=0.035

Abstract Neutron powder diffraction data have been collected in order to characterize the FRL-FRH transition of Nb-doped, Zr-rich PZT. Data for the first few diffraction peaks were obtained in the temperature range 270<T<350 K in order to make a detailed characterization of the FRL-FRH transition, which takes place for this composition at TLT≅323 K. The temperature dependence of the Pb and Zr/Ti(Nb) atomic shifts, and the rotation and distortion of the oxygen octahedra through the transition was derived. The results are compared with published data for PZT with x=0.10, and indicate that (a) the change in Zr/Ti(Nb) shift through TLH becomes more pronounced, and (b) the distortion and tilt of the oxygen octahedra below TLH become more important for x=0.035 than for x=0.10. It has been concluded that the increment in the variation of the spontaneous polarization through TLH with increasing Zr amount is mainly caused by the increase of the Zr/Ti(Nb) displacement in the low temperature rhombohedral phase.

Piezoelectric Resonance Investigation of Zr-rich PZT at Room Temperature

We study the piezoelectric resonances in poled PZT ceramics by means of a microscopic model. It connects the microscopic vibrations of the ionic units, cooperatively producing the piezoelectric effect, with the macroscopic piezoelectric parameters. The behaviour at the resonance is well described in a wide range of frequencies, allowing the calculation of piezoelectric constants and the electromechanical coupling factors in terms of microscopic quantities.

Dielectric losses and conductivity of Zr-Rich PZT

Abstract The temperature and frequency dependence of the dielectric constant and the conductivity of Zr-rich PZT (95/5 Zr/Ti ratio) has been investigated. In the paraelectric region (T>520 K) the effect of the conductivity, probably due to oxygen vacancies becomes predominant at low frequencies. At the ferro-paraelectric transition temperature, TFP , a straightforward analysis of the frequency dependence of the dielectric losses peak allows the characterization of the intrinsic relaxation time temperature dependence in the vicinity of the transition temperature.

Temperature dependence of the order parameter at the quasi-tricritical phase transition in ferroelectric TGSe

Abstract The order parameter temperature dependence near Tc has been studied in TGSe crystals with two different experimental techniques: spontaneous polarization (hysteresis loops) and increment of birefringence by means of high resolution measurements. The values of g and h, characteristic dimensionless parameters in the equation of state, are obtained, confirming the previous result g ≈ 1/3, which corresponds to quasi-tricritical behavior.

Study of the free convection effect on a standard weight using an infrared thermography imaging system

In this work, a new experimental method, based on non-invasive infrared thermograph techniques, has been developed to visualize and quantify the spatial temperature distribution of the convective air currents generated by a heated body.Starting from that distribution of temperature and using some theoretical models, the corresponding velocity distribution of the air currents and drag forces were evaluated. Once the drag forces were obtained, their values were compared with the values of mass variations taken from the balance, proving the relationship between the inverse of the drag forces and the values of the variation of mass.

Comments on the dielectric discontinuties in PZT ceramics near the ferro-paraelectric transition

Abstract A new simple method to fit the temperature dependence of the spontaneous polarization by an effective field expression is discussed. This method relays upon the experimental values of Ps∗, spontaneous polarization at T∗ > Tc, where T∗ is the transition temperature, and the ratio T∗/Tc, from dielectric constant data, assumming h=−g in the effective field expression. Data for KNbO3, PbTiO3, BaTiO3 and PZT with x(Ti)=0.035 are analyzed and they give reasonably good fits.