In this study, some structural and electrical properties of a PZT base composition Pb0.89(Ba, Sr)0.11(Zr0.52Ti0.48)O3 co-doped with 1mol% manganese and 2mol% fluorine have been studied. Two different fluorine sources were used: lead fluoride PbF2 and manganese fluoride MnF2. These fluoride salts are added to the co-precipitated precursors powder. Mn dopant was added to the solution as manganese acetate (MnAc) before co-precipitation, when PbF2 was used. The structural analysis of the sintered ceramics revealed that MnF2 doping makes the volume of the cubic unit cell (Vc) and the grain size decrease, whereas (MnAc, PbF2) co-doping makes the apparent density increase and keeps the average grain size and Vc unchanged. Both types of doping reagents largely enhance the piezoelectric activity (high d33 and k33 coefficients, well saturated Polarization–Electric field loops) but MnF2 induces both combinatory soft and hard characteristics compared to (MnAc, PbF2) co-doping. Impedance spectroscopy showed that both types of doping reagents strongly reduce the electrical conductivity with the same conducting species, i.e. the same defect chemistry, confirmed by optical absorption data. Finally, this study shows that in the semi-wet process used, PbF2 is added homogeneously to the co-precipitated powder. Whatever the fluorine source, only the coexistence of Mn and F dopants is necessary to improve the piezoelectric response.

Na0.5Bi0.5TiO3 (NBT) and its modifications are known to be new lead-free ferroelectric materials and are promising for environment friendly devices. The systems under investigation were (i) NBT (trigonal/ferroelectric)–PbZrO3 (orthorhombic/antiferroelectric); (ii) NBT (trigonal/ferroelectric)–BiScO3 (trigonal/paraelectric); and (iii) NBT (trigonal/ferroelectric)–BiFeO3 (trigonal/antiferromagnetic).

Lead free ceramics [(Na0.5Bi0.5TiO3)((1-x))(BiScO3)(x) X = 0 to 0.25] were prepared following the conventional mixed oxide route. The effect of incorporated BiSCO3 on the structure, lattice parameters and electrical properties of the NBT-BS system has been studied. The increase of the lattice parameters with x is linked to the increase of the mean ionic radii in the B-site of the perovskite structure. The Sc-Ti substitution increases the disorder in the cationic sublattice which involves an increase of the diffuseness of the structural phase transition at T-c.

In this study, ac and dc conductivity measurements were performed under ambient atmosphere on doped lead zirconate titanate (PZT) ceramics in order to investigate the defect chemistry by identifying the predominant charge carriers. The considered compositions were acceptor (1% mol Mn or Mg) and donor (Nb or F) co-doped PZTs with [Donor] = I or 2% mol.The influence of donor concentration on the conductivity was determined. From the conduction activation energy values calculated in the temperature range 200-700 degrees C, the principal contributing charge carriers are doubly-ionized oxygen V-O and lead vacancies V-Pb. For Mg doped PZTs, neither Nb nor F co-doping strongly reduce both conductivity levels and the dominant conducting species VO. For Mn doped materials, both donor co-dopants niobium and fluorine reduce the conductivity but do not have the same effect on the conduction mechanism at low temperature. With 2% Nb doping, the dominant conducting species are V-O whereas electrical conduction is controlled by electrons from the second-ionization of oxygen vacancies with 2% F doping. The difference of oxygen vacancies content in (Mn, F) and (Mn, Nb) co-doped PZTs may be at the origin of the two distinct conducting species and of the different conductivity levels. (c) 2005 Elsevier Ltd. All rights reserved.

This paper presents a model describing the hysteresis in ferroelectric materials at moderate to high driving levels. Hysteresis and nonlinearities are attributed to the irreversible displacement of domain walls. The model, based on a simple mechanism related to the dry-friction concept, is developed to describe the hysteresis of polarization and strain under electric field and stress. Besides coefficients such as ε33 and d33 also exhibit large hysteresis loops under high electric and/or mechanic level. In this paper it is shown that modeling macroscopic quantities such as P or S hysteresis lead to a reasonable estimate of the coefficients since their behavior depends mainly on polarization. The proposed approach is developed, discussed, and compared with experimental results from Navy II piezoelectric transducer ceramic. Comparisons on hysteresis loops are given and are in good agreement for the polarization and strain versus electric field and, to a less extent, for the coefficients ε33 and d33. The linear and Rayleigh regime are deduced from the proposed approach.

In this paper, we report on the effect of donor addition (Nb5+ or F-) on the electrical and piezoelectric properties and crystallographic characteristics of Mn-doped lead zirconate titanate (PZT) ceramics. Samples were prepared chemically by coprecipitation of oxalates and hydroxides. The niobium ion was incorporated in the B site whereas the fluorine ion was introduced in the anionic site. Structural analysis (XRD) and measurement of electrical properties were carried out. Electron spin resonance was used to determined the valency states of manganese in PZT ceramics. From the experimental results, the F–O substitution decreases the amount of oxygen vacancies in the Mn-doped PZT, and the valency states remain unchanged. However, a small number of oxygen vacancies may exist in PZT doped with 1 at.% manganese and 2 at.% fluorine. In the (Mn,Nb) co-doping case, the valency states vary from 4+ to 2+ and the number of oxygen vacancies is lower or even almost equal to zero. Thus the electroneutrality is achieved by lead vacancies.

Recently, it has been shown that co-doping with 1% mol. Manganese and 1% mol. fluorine a PZT base composition improved the dielectric and piezoelectric properties. A model based upon electron transfers between Mnalpha+ ions (alpha = 2, 3, 4) has been proposed to explain such a behaviour. F co-doping has been realized on Cr and Sn doped PZT to determine if the same model is valid with other acceptor dopants possibly exhibiting different valency states in the PZT (Sb, F) and (Nb, F) co-doped PZTs were also studied to estimate the influence of fluorine on the valency state of donor dopants. XRD measurements revealed that F co-doping generates lead vacancies in the cationic sublattice of Cr doped PZT instead of partially reducing cationic dopant. No change is observed in the unit cell volume and the piezoelectric properties of Sb and Nb doped PZTs after F co-doping. In the case of Sn doping, F- ion may make Sn2+ and Sn4+ coexist in the PZT but the characteristics are not as high as (Mn, F) co-doped PZT ones. The correlation between cubic unit cell volume and lead vacancies content in the PZTs was supported by flame Atomic Absorption measurements. The study confirms that the softening effect observed is not due to the increase of extrinsic lead vacancies content but to the coexistence of three valency states of the cationic dopant like Mn-+4,Mn-+3,Mn-+2.

This paper summarizes a mechanical model for characterizing hysteresis in ferroelectric materials at moderate to high drive levels. Hysteresis and nonlinearities are attributed to the displacement of domain walls. The model based on a simple mechanical element (dry friction), is developed to interpret piezo-coefficient hysteresis due to mechanical stress or electric field. The principles of basic element are given. The viability of the model is illustrated through comparison with experimental data from soft and hard PZT ceramics.

The variation of the resonant and anti-resonant frequencies of the longitudinal mode of particular doped PBSZT ceramics versus thermal cycle (+5/spl deg/C-+140/spl deg/C) is studied. A substantial thermal hysteresis of the frequencies may be observed during the first heating/cooling process for precise compositions. The study of the temperature dependence of some electromechanical coefficients has been performed to evaluate a possible influence of the frequencies change. The above mentioned hysteresis has been interpreted in terms of stabilization of ferroelectric domain configuration, widely damaged when oxygen vacancies exist in the ceramic.

The influence of (Mn, F) and (Mg, F) dopants on the piezoelectric properties of lead zirconate titanate (PZT) ceramic compositions close to the morphotropic phase boundary is investigated. PZT ceramics are prepared by a chemical route based on co-precipitation of oxalates and hydroxides. The acceptor is incorporated into the B site of the materials and the fluorine ion is introduced into anionic sites. The d33 coefficient, the mechanical quality factor Qm and other properties are measured. Scanning electron microscopy is used to determine the grain size of the materials. Electron spin resonance is used to determine the valency state of Mn in fluorinated PZT ceramics. In Mn doped PZT, the introduction of a fluorine ion makes the poling process easier and increases the piezoelectric coefficients whereas the fluorination of Mg doped PZT constantly leads to hard materials with a lower piezoelectric response. This study shows that (Mn, F) co-doping produces semihard materials with high piezoelectric coefficients.

This study concerns the reversibility of (Mn, F) co-doped PZT characteristics under thermal disturbances. PZT formulations with high piezoelectric coefficients (d(33) approximate to 320 pC/N) and exhibiting a non hysteretic frequency response between -40degrees C and -1-85degrees C have been obtained. A phenomenological model is proposed to explain these results. This model is based upon an analogy of the dopants behaviour with the fundamental laws of the redox phenomena approach in aqueous solutions. This also permits one to easily differentiate the mechanisms leading to soft and hard PZT materials.

The hysteretic behavior of the charge coefficient d33 under high mechanical stress and of frequency constant N33 during the temperature cycle −40°C–+80°C can be cancelled by fluorine oxygen substitution in the lattice of Mg-doped PZT. These fluorine doped materials also exhibit a high mechanical quality factor and low dielectric losses. The drawback is that they have a lower d33 coefficient and are difficult to pole. Mn doping in B site or La doping in A site, in the ABO3 type perovskite structure are known to increase the d33 coefficient and the poling ability. This result is observed on (Mg, F) co-doped PZT with Mn and with La content of 1.5 mol%. In the same manner, Mn doping enhances the hysteretic behavior and the losses while La doping does not significally changes the (Mg, F) co-doped PZT characteristics except the fluorine content for which the losses and the hysteresis are the lowest.

Some acceptor and fluorine co-doped PZT ceramics exhibit a low and non hysteretic dependence of d(33) coefficient under uniaxial static stress up to 120 MPa and of N-33 coefficient versus temperature between -40 degreesC and + 80 degreesC. This behavior could be explained by a strong clamping effect of the domain walls due to the acceptor ion - F dipole, less mobile than the oxygen vacancy-acceptor ion defect dipole. In order to understand the hysteresis mechanism and the role of fluorine ions, fluoridated materials with different acceptors in B site have been prepared and characterized.