There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Investigations in the development of lead-free piezoelectric ceramics have recently claimed comparable properties to the lead-based ferroelectric perovskites, represented by Pb(Zr,Ti)O3, or PZT In this work, the scientific and technical impact of these materials is contrasted with the various families of “soft” and “hard” PZTs On the scientific front, the intrinsic nature of the dielectric and piezoelectric properties are presented in relation to their respective Curie temperatures (T
 C) and the existence of a morphotropic phase boundary (MPB) Analogous to PZT, enhanced properties are noted for MPB compositions in the (Na,Bi)TiO3-BaTiO3 and ternary system with (K,Bi)TiO3, but offer properties significantly lower The consequences of a ferroelectric to antiferroelectric transition well below T
 C further limits their usefulness Though comparable with respect to T
 C, the high levels of piezoelectricity reported in the (K,Na)NbO3 family are the result of enhanced polarizability associated with the orthorhombic-tetragonal polymorphic phase transition being compositionally shifted downward As expected, the properties are strongly temperature dependent, while degradation occurs through the thermal cycling between the two distinct ferroelectric domain states Extrinsic contributions arising from domains and domain wall mobility were determined using high field strain and polarization measurements The concept of “soft” and “hard” lead-free piezoelectrics were discussed in relation to donor and acceptor modified PZTs, respectively Technologically, the lead-free materials are discussed in relation to general applications, including sensors, actuators and ultrasound transducers

Lead-free piezoelectric ceramics: Alternatives for PZT?

Potassium-sodium niobate lead-free piezoelectric materials: past, present, and future of phase boundaries.

Perovskite lead-free dielectrics for energy storage applications

The aim of this review article on recent developments of mechanochemistry (nowadays established as a part of chemistry) is to provide a comprehensive overview of advances achieved in the field of atomistic processes, phase transformations, simple and multicomponent nanosystems and peculiarities of mechanochemical reactions. Industrial aspects with successful penetration into fields like materials engineering, heterogeneous catalysis and extractive metallurgy are also reviewed. The hallmarks of mechanochemistry include influencing reactivity of solids by the presence of solid-state defects, interphases and relaxation phenomena, enabling processes to take place under non-equilibrium conditions, creating a well-crystallized core of nanoparticles with disordered near-surface shell regions and performing simple dry time-convenient one-step syntheses. Underlying these hallmarks are technological consequences like preparing new nanomaterials with the desired properties or producing these materials in a reproducible way with high yield and under simple and easy operating conditions. The last but not least hallmark is enabling work under environmentally friendly and essentially waste-free conditions (822 references).

/pdf/hallmarks-of-mechanochemistry-from-nanoparticles-to-5cyjx2wiue.pdf

Hallmarks of mechanochemistry: From nanoparticles to technology

The perovskite solid solution system (1-x)BiScO/sub 3/-(x)PbTiO/sub 3/ represents an interesting new family of high-temperature piezoelectric materials. Compositions near the morphotropic phase boundary (x /spl sim/ 0.64) have been reported to have high Curie temperatures (T/sub c/ > 450/spl deg/C) and good piezoelectric coefficients (d/sub 33/ /spl sim/ 460 pC/N). In this work, manganese additions were used to improve the high-temperature electrical resistivity and RC time constant of compositions near the morphotropic phase boundary. The addition of manganese was found to shift T/sub C/ to slightly lower temperatures (442/spl deg/C and 456/spl deg/C for x = 0.64 and x = 0.66, respectively). The piezoelectric activities of the modified materials were found to be reduced slightly due to the hardening effect of manganese; however, the temperature stability and resistivity of the modified materials were significantly enhanced. In this paper we present, for the first time, a complete set of materials constants, including the elastic (s/sub ij/, c/sub ij/), piezoelectric (d/sub ij/, e/sub ij/, g/sub ij/, h/sub ij/), dielectric (/spl epsi//sub ij/, /spl beta//sub ij/), and electromechanical (k/sub ij/) coefficients and compare them to both unmodified 0.36BiScO/sub 3/-0.64PbTiO/sub 3/ and PZT5A ceramics.

Elastic, piezoelectric, and dielectric characterization of modified BiScO/sub 3/-PbTiO/sub 3/ ceramics

The bismuth-based perovskite solid solution (100−x)BiScO3−xPbTiO3 (BSPT) was investigated for use at temperatures up to 400°C and above. The high-temperature resistivity, together with dielectric and piezoelectric behaviors of the shear mode for manganese-modified BSPT ceramics near the morphotropic phase boundary composition were studied. The resistivity and time constant were found to be 3×107Ωcm and 0.08s, respectively, at 450°C for modified BSPT66. The dielectric constant Κ11T and dielectric loss were found to be 1112 and 1%, respectively, at room temperature, showing a Curie temperature at 468°C. The electromechanical coupling factor k15 was calculated to be 61%, staying nearly constant up to 440°C, expanding the temperature usage range significantly. The properties indicate that the modified BSPT66 material is a promising candidate for high-temperature shear sensor applications.

Manganese-modified BiScO3–PbTiO3 piezoelectric ceramic for high-temperature shear mode sensor

Nonlinear ceramics that provide the basis for high-energy-density and high-temperature capacitors, as well as tunable microwave dielectrics, and their applications are discussed in this article

Nonlinear dielectric ceramics and their applications to capacitors and tunable dielectrics

The effect of Cr2O3, Nb2O5 and ZrO2 doping on the dielectric properties of CaCu3Ti4O12

The extent of BiInO3 substitution in the perovskite system xBiInO3–(1 - x)PbTiO3 and the corresponding raise in the Curie temperature were investigated using thermal analysis, dielectric measurements, x-ray diffraction, and electron microscopy. Maximum tetragonal perovskite distortion (c/a = 1.082) was obtained for x = 0.20, with a corresponding Curie temperature of 582 °C. Phase-pure tetragonal perovskite was obtained for x ⩽ 0.25. Compound formation after calcining mixed oxide powders resulted in agglomerated cube-shaped tetragonal perovskite particles, which could be fired to 94.7% of theoretical density (TD). Sol-gel fabrication resulted in nano-sized tetragonal or pseudo-cubic perovskite particles, which after two-step firing, resulted in a tetragonal perovskite microstructure at as high as (x = 0.20) 98.1% of TD.

Edward F. Alberta

Papers

Elastic, piezoelectric, and dielectric characterization of modified BiScO/sub 3/-PbTiO/sub 3/ ceramics

Manganese-modified BiScO3–PbTiO3 piezoelectric ceramic for high-temperature shear mode sensor

Nonlinear dielectric ceramics and their applications to capacitors and tunable dielectrics

The effect of Cr2O3, Nb2O5 and ZrO2 doping on the dielectric properties of CaCu3Ti4O12

High Curie temperature perovskite BiInO3 PbTiO3 ceramics