36 Result(s)

Article

Mechanical properties enhancement in potassium-sodium niobate lead-free piezoceramics: the impact of chemical modifications

The development of (K_0.44Na_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O₃-based (KNL-NTS) ceramics is attracting great interest because of environmental concerns. Most of the efforts have been concentrated on improving the el...

L. Ramajo, M. Castro, J. F. Fernandez… in Journal of Materials Science: Materials in… (2017)

Article

Influence of surface modifiers on hydrothermal synthesis of K _x Na_(1−x)NbO₃

The synthesis of potassium–sodium niobate lead-free piezoelectric ceramics has been widely studied during the past decade because of the promising industrial application of these materials. We here report the ...

L. Ramajo, F. Rubio-Marcos, A. Del Campo… in Journal of Materials Science: Materials in… (2015)

Article

Synthesis of amorphous acid iron phosphate nanoparticles

A simple method to precipitate nanoparticles of iron phosphate with acid character has been developed in which the control of pH allows to obtain amorphous nanoparticles. The acid aging of the precipitated amo...

E. Palacios, P. Leret, J. F. Fernández, A. H. De Aza… in Journal of Nanoparticle Research (2012)

Article

Quinine doped hybrid sol–gel coatings for wave guiding and optical applications

Pure and quinine doped silica coatings have been prepared over sodalime glasses. The coatings were consolidated at low temperature (range 60–180 °C) preserving optical activity of quinine molecule. We designed...

E. Enríquez, M. A. Garcia, N. Carmona… in Journal of Sol-Gel Science and Technology (2012)

Article

Effect of the temperature on the synthesis of (K,Na)NbO₃-modified nanoparticles by a solid state reaction route

(Na_0.5K_0.5)NbO₃ (KNN)-modified nano-particulated powders, based on variations of sodium–potassium niobate, were synthesised by solid state reaction from carbonate starting materials. The nanoparticles were attain...

F. Rubio-Marcos, J. J. Romero, J. F. Fernandez in Journal of Nanoparticle Research (2010)

Article

Properties of polyamide 6/clay nanocomposites processed by low cost bentonite and different organic modifiers

Nanocomposites based on polyamide 6 have been directly prepared by melt compounding, using modified low cost bentonites by three selected quaternary ammonium cations, in particular quaternized octadecylamine (...

D. García-López, I. Gobernado-Mitre, J. F. Fernández, J. C. Merino… in Polymer Bulletin (2009)

Article

The influence of area/volume ratio on microstructure and non-Ohmic properties of SnO₂-based varistor ceramic blocks

This work deals with the electrical properties of SnO₂-based varistor systems with different area–volume (A/V) ratio of the green compact. The influence of A/V ratio specially on microstructural homogeneity and d...

M. A. Ramírez, J. F. Fernández… in Journal of Materials Science: Materials in… (2009)

Article

Thermal evolution of ZnO-Bi₂O₃-Sb₂O₃ system in the region of interest for varistors

In facing the design of new processing strategies for ZnO based ceramic varistors, a precise control of its microstructural development during sintering is demanded. Addition of dopants to zinc oxide results i...

M. Peiteado, M. A. De La Rubia, J. F. Fernández… in Journal of Materials Science (2006)

Article

Electrical Properties of Bismuth Titanate Based Ceramics with Secondary Phases

Bi₄Ti₃O₁₂ (BIT) based ceramics were prepared by hydroxide coprecipitation method and subsequent treatment at 650^∘C for 1 h. Calcined BIT was doped with different amounts of WO₃ by surface do** using W(C₂H₅O)₆. ...

M. Villegas, T. Jardiel, A. C. Caballero, J. F. Fernández in Journal of Electroceramics (2004)

Article

Bulk Grain Resistivity of ZnO-Based Varistors

We study the temperature dependence of grain resistivity in ZnO ceramic varistors (300–430 K), finding a positive temperature coefficient (PTC). We devise a high-frequency procedure that allow us to obtain the...

A. C. Caballero, D. Fernández Hevia, J. de Frutos… in Journal of Electroceramics (2004)

Article

Structural Characteristics of p-Type Porous Silicon and their Relation to the Nucleation and Growth of Pores

The influence of the anodization time on some structural characteristics (dissolved mass, maximum porous layer thickness, porosity, crystallite size, etc.) of p-type porous silicon has been investigated. It is...

A. Pascual, J.F. Fernández, C.R. Sánchez, S. Manotas… in Journal of Porous Materials (2002)

Chapter

Bi₄Ti₃O₁₂-Based Piezoelectric Ceramics for High Temperature Applications

High temperature piezoelectric ceramics based on WO₃-doped Bi₄Ti₃O₁₂ (WBIT) were prepared by two ways: chemical (hydroxide coprecipitation) and conventional oxides mixing. Sintering was carried out between 800°-1...

M. Villegas, A. C. Caballero, C. Moure… in Piezoelectric Materials: Advances in Scien… (2000)

Article

Effect of humidity on the electrical response of porous BaTiO3 ceramics

A. C. Caballero, M. Villegas, J. F. Fernández… in Journal of Materials Science Letters (1999)

Article

Phase transition and electrical conductivity in the system YMnO3-CaMnO3

Solid solution formation between the ferroelectric hexagonal compound YMnO₃ and the semiconducting perovskite compound CaMnO₃ has been studied in the Y-rich region of the pseudobinary system. The materials were p...

C. Moure, M. Villegas, J. F. Fernandez, J. Tartaj, P. Duran in Journal of Materials Science (1999)

Article

Lower air-crystallization temperature and nanostructured yttria-doped tetragonal zirconia polycrystals ceramics by seeding assisted chemical coprecipitation

The crystallization temperature of yttria-doped tetragonal zirconia polycrystals (Y-TZP) amorphous precursors can be lowered 150 °C below that currently used (≥500 °C), if “seeding assisted chemical coprecipit...

P. Durán, J. Tartaj, J. F. Fernández, C. Moure in Journal of Materials Research (1999)

Article

Effects of PbO excess in Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ ceramics: Part I. Sintering and dielectric properties

The influence of the presence of free PbO on densification, the perovskite/pyrochlore phase ratio, and corresponding dielectric properties has been studied for 0.9 PMN–0.1 PT-based ceramics with different adde...

M. Villegas, A. C. Caballero, M. Kosec, C. Moure… in Journal of Materials Research (1999)

Article

Indication of a phase transition in the C15 Laves phase TaV2D1.8 at low temperatures

M. KEMALI, DALIN SUN, M. MERCER, J. F. FERNANDEZ… in Journal of Materials Science Letters (1998)

Article

Nanostructured and near defect-free ceramics by low-temperature pressureless sintering of nanosized Y-TZP powders

Nanosized (∼6 nm) Y-TZP (3 mol% Y₂O₃) powders have been produced by chemical co-precipitation (Y-inorganic + Zr-organic precursors) and thorough isopropanol-washing step, after calcining in air at 450 °C. The nan...

P DURAN, M VILLEGAS, F CAPEL, J. F FERNANDEZ, C MOURE in Journal of Materials Science (1997)

Article

Seeding effects on crystallization of air-calcined Y-TZP amorphous precursors

J. TARTAJ, C. MOURE, J. F. FERNANDEZ, P. DURAN in Journal of Materials Science Letters (1997)