David P. Cann

Investigation of the dielectric properties of bismuth pyrochlores

The dielectric properties of polycrystalline bismuth-based pyrochlores of the general chemical form Bi2(B232+B435+)O7 and Bi2(B3+B5+)O7 where B2+ = Mg, Cu, Zn and Ni, B3+ = Sc and In, and B5+ = Nb and Ta, were investigated as a function of temperature and frequency. At low temperatures (T ∼ 100−150 K), a dielectric dispersion was universally observed within these systems. The dielectric dispersion was analyzed using phenomenological models often used for describing dipolar glass systems. Similar activation energies and pre-exponential damping frequencies are found to exist with dipolar glasses such as RADP (RbxH2PO4(NH4)1−xH2PO4), K1−xLixTaO3, KBr1−xCNx and KI1−x(NO2)x.

The morphotropic phase boundary and dielectric properties of the xPb(Zr1∕2Ti1∕2)O3-(1−x)Pb(Ni1∕3Nb2∕3)O3 perovskite solid solution

The solid solution between the normal ferroelectric Pb(Zr1∕2Ti1∕2)O3 (PZT) and relaxor ferroelectric Pb(Ni1∕3Nb2∕3)O3 (PNN) was synthesized by the columbite method. The phase structure and dielectric properties of xPZT-(1−x)PNN where x=0.4–0.9 and the Zr∕Ti composition was fixed close to the morphotropic phase boundary (MPB) were investigated. With these data, the ferroelectric phase diagram between PZT and PNN has been established. The relaxor ferroelectric nature of PNN gradually transformed towards a normal ferroelectric state towards the composition 0.7PZT-0.3PNN, in which the permittivity was characterized by a sharp peak and the disappearance of dispersive behavior. X-ray diffraction analysis demonstrated the coexistence of both the rhombohedral and tetragonal phases at the composition 0.8PZT-0.2PNN, a new morphotropic phase boundary within this system. Examination of the dielectric spectra indicates that PZT-PNN exhibits an extremely high relative permittivity near the MPB composition. The permitti...

Effects of ZrO2 additions on the dielectric properties of CaCu3Ti4O12

The dielectric spectra of CaCu3Ti4O12 is characterized by a large permittivity (er>10000) with only a weak dependence on temperature over the temperature range 200–400 K. In this work, doping with 0.1–1.0 wt % ZrO2 has been shown to dramatically reduce the dielectric loss. At 0.5 wt % ZrO2,tanδ remains below 0.05 over the frequency range 50 Hz–30 kHz and is just 0.065 at 100 kHz. While there is some diminution of the permittivity (er≈5000 at 10 kHz) Zr-doped ceramics, exhibited very little bias dependence (ΔC∕C0<1.0% up to 40 V). In summary, results suggest that ZrO2 doping is an effective method for maintaining a high permittivity and low loss over a broad range in temperature, bias, and frequency.

Phase transitions and dielectric properties in Bi(Zn1/2Ti1/2)O3−BaTiO3 perovskite solid solutions

A group of (1¿x)Bi(Zn1/2Ti1/2)O3-¿ABO3 (ABO3=BaTiO3, NaNbO3, BiScO3 and Bi1/2K1/2TiO3) polycrystalline ceramics were prepared by solid-state processing techniques. Based on x-ray diffraction results, the presence of Bi(Zn1/2Ti1/2)O3 in the solid solution decreases the structure stability of perovskite phase. The dielectric characterization revealed that the trends of transition temperature Tm as a function of composition of Bi(Zn1/2Ti1/2)O3-ABO3 could be described into two groups. The first one is Tm decreased until second phase appeared and the second one is Tm decreased and then increased as Bi(Zn1/2Ti1/2)O3 content increased. In addition, with substitution of Li for Na of NaNbO3-Bi(Zn1/2Ti1/2)O3 the diffuseness of the transition peak decreased and transition temperature increased.

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1∕2Ti1∕2)O3-BaTiO3 solid solutions

Ceramics solid solutions within the ternary perovskite system Bi(Zn1∕2Ti1∕2)O3-BiScO3-BaTiO3 were synthesized via solid-state processing techniques. The crystal structure of sintered ceramics was analyzed by x-ray diffraction. A stable perovskite phase was obtained for all compositions with a BaTiO3 content greater than 50 mol %. Furthermore, a change in symmetry from pseudocubic to tetragonal was observed as the mole fraction of BaTiO3 increased. Dielectric measurements show a dielectric anomaly associated with a phase transformation over the temperature range of 30 °C–210 °C for all compositions. Examination of the polarization hysteresis behavior revealed weakly nonlinear hysteresis loops. With these data, ferroelectric phase diagrams were derived showing the transition between the pseudocubic relaxor behavior to the tetragonal normal ferroelectric behavior. This transition was also correlated with changes in the diffuseness parameter.

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.

Perovskite phase formation and ferroelectric properties of the lead nickel niobate-lead zinc niobate-lead zirconate titanate ternary system

The ternary system of lead nickel niobate Pb(Ni 1 / 3 Nb 2 / 3 )O 3 (PNN), lead zinc niobate Pb(Zn 1 / 3 Nb 2 / 3 )O 3 (PZN), and lead zirconate titanate Pb(Zr 1 / 2 Ti 1 / 2 )O 3 (PZT) was investigated to determine the influence of different solid state processing conditions on dielectric and ferroelectric properties. The ceramic materials were characterized using x-ray diffraction, dielectric measurements, and hysteresis measurements. To stabilize the perovskite phase, the columbite route was utilized with a double crucible technique and excess PbO. The phase-pure perovskite phase of PNN-PZN-PZT ceramics was obtained over a wide compositional range. It was observed that for the ternary system 0.5PNN-(0.5- x)PZN-xPZT, the change in the transition temperature (T m ) is approximately linear with respect to the PZT content in the range x = 0 to 0.5. With an increase in x, T m shifts up to high temperatures. Examination of the remanent polarization (P r ) revealed a significant increase with increasing x. In addition, the relative permittivity (∈ r ) increased as a function of x. The highest permittivities (∈ r = 22,000) and the highest remanent polarization (P r = 25 μC/cm 2 ) were recorded for the binary composition 0.5Pb(Ni 1 / 3 Nb 2 / 3 )O 3 -0.5Pb(Zr 1 / 2 Ti 1 / 2 )O 3 .

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...

Fabrication of photonic band gap materials using microtransfer molded templates

A method of manufacturing photonic band gap structures operable in the optical spectrum has been presented. The method comprises the steps of creating a patterned template for an elastomeric mold, fabricating an elastomeric mold from poly-dimethylsiloxane (PDMS) or other suitable polymer, filling the elastomeric mold with a second polymer such as epoxy or other suitable polymer, stamping the second polymer by making contact with a substrate or multilayer structure, removing the elastomeric mold, infiltrating the multilayer structure with ceramic or metal, and heating the multilayer structure to remove the second polymer to form a photonic band gap structure.

Lead-free ternary perovskite compounds with large electromechanical strains

Lead-free compounds based on perovskite solid solutions in the ternary system (Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3–Bi(X1/2Ti1/2)O3, where X = Ni and Mg have been shown to exhibit large electromechanical strains. While the perovskite end members Bi(Mg1/2Ti1/2)O3 and Bi(Ni1/2Ti1/2)O3 display limited stability in their pure state, both compounds were found to have solid solubilities of at least 50 mol. % with (Bi1/2Na1/2)TiO3 and (Bi1/2K1/2)TiO3. Most importantly, under relatively large applied fields, these materials exhibited large hysteretic electromechanical strains characterized by a parabolic shape. With effective piezoelectric coefficients (d33*) greater than 500 pm/V, these systems have excellent potential as a Pb-free piezoelectric materials.