Pb(Ti, Zr)O3 ceramics doped with Al, Mn or Fe exhibit constricted or asymmetrically displaced hysteresis loops. This distortion is due to an internal bias field Ei which can exceed the coercive field strength. Ei depends on the Ti/Zr ratio and on the kind of dope, and it increases with increasing doping concentration.After repeated cycling of the hysteresis loop the distortion disappears. This process, called “hysteresis relaxation,” obeys a time law of the form Ei(t) ∼exp(-t/τ)and is found to behave both like a field and thermally activated process. The activation energy of all investigated specimens doped with transition metal ions (Mn, Fe) lies between 0.6 and 0.7 eV, that of Al-doped samples is about 0.8 eV.Comparison of the behaviour of the dielectric and mechanical losses with that of the internal bias shows that these effects are closely correlated. From this correlation some conclusions can be drawn concerning the nature of Ei, the physical causes of the observed after-effects, and the influence o...

Electrical after-effects in Pb(Ti, Zr)O3 ceramics

The influence of Mg doping on the materials properties of Ba1−xSrxTiO3 thin films for tunable device applications

Microstructure, dielectric, ferroelectric and piezoelectric properties of bismuth sodium titanate (Bi1/2Na1/2)TiO3 (BNT) were studied for a candidate as lead-free piezoelectric ceramics. In the case of Mn addition, the Curie temperature, Tc, decreases rapidly with increasing amount of doped MnCO3. The resistivity, ρ, is enhanced to 3×1014 (Ωcm) (at 40°C) for BNT+MnCO3 0.2 (wt.%) and electromechanical coupling factor, k33, was obtained the relatively high value under the condition of the low poling field, Ep for the Mn-doped BNT ceramics. It seems that Mn ions exist in the grain, and substitute for the A- or B-site of the perovskite structure, and eject Bi ions to the air.

Additive effects on electrical properties of (Bi1/2Na1/2)TiO3 ferroelectric ceramics

Multi-frequency and pulsed electron paramagnetic resonance (EPR) provides a sensitive spectroscopic tool to elucidate the defect structure of transition-metal doped perovskite oxides, as well as to monitor dynamic processes of oxygen vacancies in these materials. In this regard, high-frequency EPR spectrometers and pulsed EPR techniques such as the hyperfine sublevel correlation experiment (HYSCORE) may now routinely be used for dedicated investigations, providing considerably more insight than the application of standard continuous-wave EPR. Recent results include the formation of defect complexes between acceptor-type transition-metal centers with either one or two oxygen vacancies for the reason of charge compensation. Furthermore, such defect complexes follow the domain switching upon poling ferroelectric compounds with correspondingly high electric fields. On the other hand, multi-valent manganese functional centers provide trapping centers for electronic and ionic charge carriers (e', ) such that valency altered acceptor states or defect complexes are formed. Additionally, the trapping of charge carriers at the intrinsic 'reduced' B-site ions, and , can be observed by means of EPR spectroscopy.

Structural and dynamic properties of oxygen vacancies in perovskite oxides—analysis of defect chemistry by modern multi-frequency and pulsed EPR techniques

Pure and La doped Ba0.6Sr0.4TiO3 thin (BST) films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors on Pt–Si substrates. The La doping concentration, from 0 to 10 mol %, was found to have a strong influence on the 750 °C postdeposition annealed films material properties. All films possessed a nontextured polycrystalline microstructure with no evidence of secondary phase formation. The pure and 1 mol % La doped films exhibited a uniform microstructure suggestive of a fully developed film at this annealing temperature. Improved dielectric and insulating properties were achieved for the 1 mol % La doped BST thin films with respect to that of undoped BST films. The 1 mol % La doped BST film exhibited a lower dielectric constant, (283 vs 450) and enhanced resistivity (31.4×1013 Ω cm vs 0.04×1013 Ω cm) with respect to that of undoped BST films. The loss tangent and tunability (at 100 kHz) of the 1 mol % La doped BST films were 0.019% and 21% (at E=300 kV/cm...

La doped Ba1−xSrxTiO3 thin films for tunable device applications

An investigation of the effects of small additions of Fe2O3 to lead zirconate-lead titanate ceramics with compositions between 45 and 60 mol% lead zirconate has shown that, with 2 moles of PbO to balance each mole of Fe2O3, the solubility of Fe2O3 was about 0.8 wt% in compositions near the tetragonal-rhombohedra1 boundary. The dielectric constant and dissipation factor for both rhombohedra1 and tetragonal materials were decreased by addition of iron oxide, whereas the mechanical quality factor and frequency constant were increased. The dependence of the electromechanical properties on grain size was qualitatively similar for both undoped and iron oxide-doped materials; the presence of iron oxide inhibited grain growth and lowered the limiting grain size below which the electromechanical properties change rapidly with grain size.

V M McNamara

Papers

Lead Zirconate‐Lead Titanate Piezoelectric Ceramics with Iron Oxide Additions

Variations in properties with composition in lead zirconate-titanate ceramics