Pyroelectric Charge Release in Rhombohedral PZT

A new experimental set-up controlled by computer has been made to measure the pyroelectric charge of ferroelectric materials with a relatively high conductivity at slow rates of temperature variation. It allowed us to obtain the polarisation vs. temperature behaviour of PZT with various compositions in the whole range of temperatures with a high accuracy. The ferroelectric Zr-rich region of the PZT phase diagram, where the isostructural phase transition FRL-FRH takes place, has been studied

Propiedades dieléctricas, piroeléctricas y piezoeléctricas de PZT cerámico rico en circonio

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Materiales. Fecha de lectura: 10-6-199

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.

Tilts and Ionic Shifts in Rhombohedral Perovskites

We make a comparative analysis of rhombohedral perovskites (ABO3) with/without oxygen rotations and ionic shifts, within the framework of a generalised effective field approach. We analyse available data on LaAlO3 and LiTaO3 and new data on Zr-rich PZT, examples of three different ways of structural evolution with temperature of the rhombohedral perovskites. The coupling between polarization and tilt is studied in detail in PZT and a possible coupling between tilt and polarization in LiTaO3 is discussed.

Composition dependence of the ferroelectric-paraelectric transition in the mixed system PbZr1–xTixO3

The dielectric constant and losses of good quality ceramic samples of Nb-doped (1 wt % Nb2O5) PbZr1–xTixO3 about the ferroelectric-paraelectric transition for 0.03≤x≤0.09 have been measured with the aim of investigating the behavior of the thermal hysteresis with composition and the possible existence of tricritical points in this mixed system. The trend of the data, analyzed in terms of a generalized effective-field theory (Eeff=E+βP+γP3+ • • • ) indicates that two tricritical points, at x ≈0.26 and x ≈0.51, are implied by the observed behavior at lower x

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.