M.E. Villafuerte-Castrejón

Superstructure determination of the perovskite βLa0.33NbO3

New interesting results in the crystal structure of the perovskite βLa0.33NbO3 were revealed using selected area electron diffraction, powder X-ray diffraction techniques and Rietveld refinement method. Although the superstructure of βLa0.33NbO3 could not be seen by conventional X-ray powder diffraction technique, the electron diffraction patterns revealed weak spots resulting in a superstructure array for the atoms of βLa0.33NbO3. The crystal symmetry is compatible with an orthorhombic cell, space group Cmmm. From Rietveld refinement, the resulting lattice parameters are: a = 7.82(1) Å, b = 7.83(9) Å, c = 7.90(9) Å and goodness of fit R = 0.1107, Rwp = 0.15. The superstructure is built from distorted octahedra NbO6 along the [001] axis. Results suggest that this distortion may be produced by occupation of La atoms in (2a) and (4l) sites.

Lead-Free Ferroelectric Ceramics with Perovskite Structure

Ferroelectric ceramics were discovered in the 1940s in polycrystalline barium titanate (von Hippel et al., 1946; Wul & Goldman, 1945), since then, there has been a continuous succession of new materials and technology developments that have led to a significant number of industrial and commercial applications. Structurally speaking there are four types of ferroelectric ceramics: (1) perovskites, (2) the tungsten-bronze group, (3) pyrochlores and (4) the bismuth layer-structure group. Of these, the perovskites (ABO3) are by far the most important category. The families with composition BaTiO3, PbZr1-xTixO3 (PZT), PZT:La (PLZT), PbTiO3 (PT), Pb(Mg1/3Nb2/3)O3 (PMN) and (K0.5Na0.5)NbO3 (KNN) represents most of the ferroelectric ceramics manufactured in the world (Haertling, 1999). In this chapter the structure of calcium titanium oxide (CaTiO3), the ferroelectrics ceramics BaTiO3, Na0.5Bi0.5TiO3 (NBT), K0.5Bi0.5TiO3 (KBT) are described as well the concept of hysteresis loop, ferroelectric domains and why lead free materials are now in the top of the interest in ferroelectric and piezoelectric materials. The aim of this chapter is to present results of the synthesis, characterization and piezoelectric properties of two lead free piezoelectric compounds: K0.5Na0.5NbO3 and (K0.48Na0.52)0.96Li0.04Nb0.85Ta0.15O3.

Sub-10 μm grain size, Ba1−xCaxTi0.9Zr0.1O3 (x = 0.10 and x = 0.15) piezoceramics processed using a reduced thermal treatment

The solid-state synthesis of Ba1−xCaxTi0.9Zr0.1O3 (x = 0.10, 0.15) (BCTZ) powder and the processing method of ceramics, by the use of reduced synthesis time and temperature (1250 °C for 2 h), are reported. Homogeneous and dense (≥95%) ceramic microstructures with sub-10 μm grain size were obtained under all sintering conditions. A comparative study of their ferro-piezoelectric properties as a function of sintering temperatures is presented. The study shows the role of the grain size effect for improving both piezoelectric and ferroelectric properties of these materials. With an increase of the sintering temperature, grain growth was promoted; therefore, higher ferro-piezoelectric values were obtained (at 1400 °C, for x = 0.10: d33 = 300 pC/N, kp = 48%; for x = 0.15: d33 = 410 pC/N, d31 =–154 pC/N, kp = 50%). In addition, a diffuse phase transition is observed in these BCTZ ceramics with a Curie temperature near 100 °C at 1 kHz.

Piezoelectric Ceramics of the (1 − x)Bi0.50Na0.50TiO3–xBa0.90Ca0.10TiO3 Lead-Free Solid Solution: Chemical Shift of the Morphotropic Phase Boundary, a Case Study for x = 0.06

Research and development of lead-free piezoelectric materials are still the hottest topics in the field of piezoelectricity. One of the most promising lead-free family of compounds to replace lead zirconate–titanate for actuators is that of Bi0.50Na0.50TiO3 (BNT) based solid solutions. The pseudo-binary (1 − x)Bi0.50Na0.50TiO3–xBa1 − yCayTiO3 system has been proposed for high temperature capacitors and not yet fully explored as piezoelectric material. In this work, the solid solution with x = 0.06 and y = 0.10 was obtained by two different synthesis routes: solid state and Pechini, aiming at using reduced temperatures, both in synthesis (<800 °C) and sintering (<1150 °C), while maintaining appropriated piezoelectric performance. Crystal structure, ceramic grain size, and morphology depend on the synthesis route and were analyzed by X-ray diffraction, together with scanning and transmission electron microscopy. The effects of processing and ceramic microstructure on the structural, dielectric, ferroelectric, and piezoelectric properties were discussed in terms of a shift of the Morphotropic Phase Boundary, chemically induced by the synthesis route.

Optical and Piezoelectric Study of KNN Solid Solutions Co-Doped with La-Mn and Eu-Fe

The solid-state method was used to synthesize single phase potassium-sodium niobate (KNN) co-doped with the La3+–Mn4+ and Eu3+–Fe3+ ion pairs. Structural determination of all studied solid solutions was accomplished by XRD and Rietveld refinement method. Electron paramagnetic resonance (EPR) studies were performed to determine the oxidation state of paramagnetic centers. Optical spectroscopy measurements, excitation, emission and decay lifetime were carried out for each solid solution. The present study reveals that doping KNN with La3+–Mn4+ and Eu3+–Fe3+ at concentrations of 0.5 mol % and 1 mol %, respectively, improves the ferroelectric and piezoelectric behavior and induce the generation of optical properties in the material for potential applications.

Eu1.8La0.2BaZnO5: a Rietveld refinement using X‐ray powder diffraction

The families of oxides with stoichiometry RE2BaMO5 (where RE is a trivalent rare earth, and M is Co2+, Ni2+, Cu2+, Zn2+, Pd2+ or Pt2+) are known as the green phases in studies of Y–Ba–Cu–O superconductor ceramics. These oxides are not superconductors but nevertheless present interesting structural types. In this work, the synthesis and structural characterization using the Rietveld method applied to X-ray powder diffraction data for Eu1.8La0.2BaZnO5 (europium lanthanum barium zinc oxide) are presented. The compound is isostructural with Y2BaZnO5. The two sites for Y3+ are occupied by Eu3+, while La3+ ions partially occupy one of these sites.

γ-Sodium gallate: a Rietveld refinement using X-ray powder diffraction

Tetrahedrally coordinated oxides usually present polymorphism, but for NaGaO2, only the β polymorph has been reported. In this work, the synthesis and structural characterization of γ-sodium gallate, γ-NaGaO2, are presented. The crystal structure belongs to the orthorhombic system, space group Pbca (No. 61), and has been characterized by a Rietveld refinement of the X-ray powder diffraction pattern. The structure is similar to those exhibited by the γ phases of many tetrahedral oxides.

Piezoelectric, Dielectric and Ferroelectric Properties of (1−x)(K0.48Na0.52)0.95Li0.05Nb0.95Sb0.05O3-xBa0.5(Bi0.5Na0.5)0.5ZrO3 Lead-Free Solid Solution

The lead-free solid solution

Development of AlN and TiB2 Composites with Nb2O5, Y2O3 and ZrO2 as Sintering Aids

(1-x)