Rigoberto López-Juárez

High spatial resolution structure of (K,Na)NbO3 lead-free ferroelectric domains

In this paper, we highlight some practical aspects in the study of ferroelectric domains in lead-free (K,Na)NbO3 piezoceramics. This work presents and discusses the spatial resolved structure of the ferroelectric domain existing in (K,Na)NbO3 based ceramics studied by confocal Raman microscopy (CRM) coupled with atomic force microscopy. In addition to the domain identification, CRM allows a determination of the nature of domain walls and correlation between the structure and piezoelectric properties. The tetragonal constraint for orthorhombic domain formations is demonstrated by this technique. Alternating polarization differences in 180° domain templates are resolved by 60° and 120° domains. The internal stress results in the appearance of an unusual polarization relaxation at the 90° domain wall in (K,Na)NbO3 ceramics. Finally, the implications of the present findings introduce a fruitful discussion in the search for effective structures to improve the piezoelectric response and represent the key point to design new domains that allow engineering the piezoelectric response.

Lead-Free Piezoceramics: Revealing the Role of the Rhombohedral–Tetragonal Phase Coexistence in Enhancement of the Piezoelectric Properties

Until now, lead zirconate titanate (PZT) based ceramics are the most widely used in piezoelectric devices. However, the use of lead is being avoided due to its toxicity and environmental risks. Indeed, the attention in piezoelectric devices has been moved to lead-free ceramics, especially on (K,Na)NbO3-based materials, due to growing environmental concerns. Here we report a systematic evaluation of the effects of the compositional modifications induced by replacement of the B-sites with Sb(5+) ions in 0.96[(K0.48Na0.52)0.95Li0.05Nb1-xSbxO3]-0.04[BaZrO3] lead-free piezoceramics. We show that this compositional design is the driving force for the development of the high piezoelectric properties. So, we find that this phenomenon can be explained by the stabilization of a Rhombohedral-Tetragonal (R-T) phase boundary close to room temperature, that facilities the polarization process of the system and exhibits a significantly high piezoelectric response with a d33 value as high as ∼400 pC/N, which is comparable to part soft PZTs. As a result, we believe that the general strategy and design principles described in this study open the possibility of obtaining (K,Na)NbO3-based lead-free ceramics with enhanced properties, expanding their application range.

Synthesis of advanced ceramics by hydrothermal crystallization and modified related methods

The present article aims to give a brief overview about the advantages of the hydrothermal crystallization method for the synthesis of advanced ceramics. Emphasis is given, not only on the conventional hydrothermal crystallization, but also on some of its variants; such as ultrasound-assisted, electrochemical-assisted, microwave-assisted and surfactant-assisted hydrothermal methods which open up new opportunities for the synthesis of ceramic materials with novel properties demanded for advanced applications. In the current work the synthesis of barium titanate (BaTiO3), lithium metasilicate (Li2SiO3) and sodium-potassium niobate (Na, K)NbO3 powders are reported as cases of study.

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.

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.

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

Ferroelectric domain structure of lead-free potassium-sodium niobate ceramics

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