Eric A. Patterson

Bipolar piezoelectric fatigue of Bi(Zn0.5Ti0.5)O3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 Pb-free ceramics

The piezoelectric fatigue behavior of Pb-free ceramics based on solid solutions of Bi(Zn0.5Ti0.5)O3-(Bi0.5K0.5)TiO3-(Bi0.5Na0.5)TiO3 was characterized at 50 kV/cm after 106 bipolar cycles. Ferroelectric compositions containing 2.5% Bi(Zn0.5Ti0.5)O3 exhibited only minor losses in maximum strain (∼10%). In compositions with 5% Bi(Zn0.5Ti0.5)O3 that exhibit large electric field-induced strains, the electromechanical strain actually increased 4%, exhibiting essentially fatigue free behavior. This finding demonstrates that these materials have excellent potential for demanding high cycle applications such as microelectromechanical systems actuators.

Electromechanical strain in Bi(Zn1/2Ti1/2)O3–(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 solid solutions

Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O3–(Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing Tmax of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT–40BKT–57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT–BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 μC/cm2 at 2.5% BZT) as BZT contents was increased (Pr = 2.3 μC/cm2 at 20% BZT). Similarly, as the temperature increased to 175 °C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 μC/cm2. The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous tran...

Enhanced bipolar fatigue resistance in CaZrO3-modified (K,Na)NbO3 lead-free piezoceramics

The bipolar fatigue behavior of (K,Na)NbO3 (KNN)-based lead-free piezoceramics was investigated. A comparative analysis demonstrated that CaZrO3-modified KNN ceramics exhibited highly enhanced bipolar fatigue resistance due to the reduced lattice distortion (c/a ratio) and coexistence of orthorhombic and tetragonal phases. The hypothesis was verified by systematical studies of cycle-dependent large and small signal parameters and micro-morphologies. It was identified that mechanical stress induced microstructure damage beneath the electrodes renders the KNN ceramics to be vulnerable to bipolar cycling; while the mild fatigue behavior for CaZrO3-modified ones mainly originates from a thermally reversible domain wall pinning.

Introducing a large polar tetragonal distortion into Ba-doped BiFeO3 by low-temperature fluorination.

This article reports on the synthesis and crystallographic and magnetic structure of barium-doped BiFeO3 compounds with approximate composition Bi(1-x)Ba(x)FeO(3-x/2), as well as those of the fluorinated compounds Bi(1-x)Ba(x)FeO(3-x)F(x) (both with x = 0.2, 0.3), prepared by low-temperature fluorination of the oxide precursors using polyvinylidenedifluoride. Whereas the oxide compounds were obtained as cubic (x = 0.2) and slightly tetragonal (x = 0.3, c/a ≈ 1.003) distorted perovskite compounds, a large tetragonal polar distortion was observed for the oxyfluoride compounds (c/a ≈ 1.08 for x = 0.2 and ∼1.05 for x = 0.3), being isostructural to tetragonal PbTiO3. Although described differently in previous reports on Ba-doped BiFeO3, the observed remanent magnetization is found to agree well with the amount of BaFe12O19 only detectable by neutron diffraction and the well-known magnetic properties of BaFe12O19. The oxyfluoride compounds show G-type antiferromagnetic ordering with magnetic moments lying in the a/b plane.

DC-bias dependent impedance spectroscopy of BaTiO3–Bi(Zn1/2Ti1/2)O3 ceramics

This report discusses the voltage-stability of the dielectric and transport properties of BaTiO3–Bi(Zn1/2Ti1/2)O3 (BT–BZT) ceramics which have shown excellent properties for emerging energy applications. For p-type BaTiO3, the ceramics deviated from Ohm’s law behavior at very low voltage levels along with a reversible drop in bulk resistivity by several orders of magnitude starting at bias fields as low as 0.1 kV cm^-1 (~8 V). In contrast, n-type BT–BZT ceramics exhibited a small (i.e. less than one order of magnitude) increase in resistivity on application of small field levels. These data indicate a hole-generation mechanism which becomes active at a low voltage threshold. The bulk capacitance values calculated using AC impedance spectroscopy, however, were relatively unaffected (<15% change) by this application of a DC bias (up to ~0.25 kV cm^-1). These findings provide important insights into the electric transport mechanisms in BT-based ceramics.