A. Fundora

Dielectric properties of the La3+ doped Sr0.3-3y/2LayBa0.7Nb2O6 ceramic system

Abstract A process for obtaining Sr 0.3− 3y 2 La y Ba 0.7 Nb 2 O 6 (LSBN) ceramics at different concentrations of the La3+ cation and different sintering times is presented. The dielectric properties of the LSBN system where Sr2+ ions are substituted by La3+ cations follow the pattern of a modification by cationic substitution for a constant Sr Ba ratio. This behavior of the dielectric properties indicate that the La3+ cations occupy the A1 as well as the A2 sites which favors the formation of the LSBN system up to y

Dielectric Properties of La3+ Doped Sr0.3–3y/2Lay Ba0.7Nb2O6 Ceramics Prepared under Different Sintering Conditions*

A study of the dielectric properties of the Lanthanum doped Sr0.3Ba0.7Nb2O6 (SBN30) ceramic according to the stoichiometric formulation Sr0.3–3y/2LayBa0.7Nb2O6 with y = 0.01, 0.03 and 0.05, and the influence of the sintering conditions is reported. The XRD shows single phase compounds for Sr0.285La0.01Ba0.7Nb2O6 (LSBN1) and Sr0.225La0.03Ba0.7Nb2O6 (LSBN3) ceramics, both samples having similar microstructure, densification and dielectric properties. The density increases linearly with ln t, where t is the sintering time, and the values of the maximum ferroelectric peaks of the permittivity increase steadily with t. Using the Bruggeman model to estimate the theoretical permittivity, it is concluded that the magnitude of the experimental permittivity peaks are mainly affected by the volume fraction of porosity of the samples. In this study we also establish that pore diffusion mechanisms behave according to the Ginstling-Brownshtein equation. For the Sr0.225La0.05Ba0.7Nb2O6 (LSBN5) sample, XRD analysis reveals the presence of isostructural compounds of the intermediate phases BaNb2O6 and SrNb2O6, and the dielectric properties start to deteriorate. This fact indicates the existence of a solubility limit of Lanthanum ions in the SBN solid solution.

Ferroelectric properties of the La0.03Sr0.255Ba0.7Nb2-yTiyO6-y/2 ceramic system

The study of the dielectric properties of the stoichiometric Titanium doped Sr0.255La0.03Ba0.7Nb2O6 ceramics prepared according to the formula Sr0.225La0.03Ba0.7Nb2–yTiyO6–y/2 is reported. A single phase compound is observed for low Ti content (y<0.1) in the XRD spectra, being isostructural with the SBN phase. For high Ti concentrations (y<0.1), the XRD patterns show, besides the SBN phase reflections, several small peaks associated with an additional phase present in the ceramics. A possible liquid phase sintering is analyzed. Strongly broadened dielectric curves are obtained in dielectric measurements, where the transition temperature decreases with the Titanium content. The diffuse phase transition coefficients are calculated, corroborating that Titanium increases the diffuse character of the transition in the monophasic region.

Evidence of short-range antiferroelectric local states in lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric ceramics

Structural and electrical measurements were performed on lanthanum- and titanium-modified Sr0.3Ba0.7Nb2O6 ferroelectric (FE) ceramics. Dielectric properties show a well-defined relaxor anomaly around −50 °C with double-loop hysteresis curves from this point to the transition temperature. The thesis of short-range antiferroelectric (AFE) local states having incommensurate (INC) structure embedded in the FE polar matrix is proposed to explain the observed behavior. Structural lattice parameters show negative expansion coefficients and INC superlattice diffraction spots were observed through the selected-area diffraction patterns in the [110] zone for this minority local states. The titanium modification of this system seems to be the key fact in the coupling of the INC structure to the AFE local states in the FE–AFE coexistence region.

Study by high resolution electron microscopy and electron diffraction of the La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2 ferroelectric ceramic

The stoichiometric La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2 (LSBNT) ceramic system was obtained for three different concentrations of titanium ions (y=1%, 3%, and 5%) where the Nb5+ was substituted by Ti4+ according to the expression La0.03Sr0.255Ba0.7Nb2−yTiyO6−y/2. The incommensurate modulation in the LSBNT structure has been studied by high-resolution transmission electron microscopy (HRTEM) and electron diffraction. The location of the incommensurate superlattice spots in the tetragonal phase through the [110] zone in the electron diffraction patterns was measured to determine the incomensuration parameter δ. Structural modulation was also evident by HRTEM for the [001] zone, where a sinusoidal variation along [110] and [110] was identified in coincidence with the electron diffraction patterns. Random occupation of the crystallographic sites that promotes structural variations may be the cause for structural incommensuration. It was possible to identify directly the tetragonal tungsten bronze structure and t...

Induced piezoactivity in the 3(1 - x)PMN - xPT solid solution

PNS ceramics present piezoactivity under an applied d.c. bias field. The relative dielectric permittivity varies, in general over a wide range of values of the applied d.c. electric field. The purpose of this work is to study the induced piezoactivity effect produced by an applied d.c. electric field in the 3(1− x ) PMN− x PT ( x −0.1) system assuming that the relative dielectric permittivity is a function of the applied d.c. electric field. An expression to calculate the electrostrictive coefficient Q 31 by measuring the coupling factor K p and the dielectric permittivity as functions of the applied electric field is presented.

Diffuse phase transition in the (La0.03Sr0.255Ba0.7)(Nb2-yTiy)O6-y/2 ferroelectric ceramic system

Abstract The effect of the titanium cation as a doping element in the diffuse phase transition of the (Sr0.255La0.03Ba0.7)(Nb2-yTiy)O6-y/2 ferroelectric ceramic system is studied. Far from the transition temperature, a Curie-Weiss behavior of the dielectric permittivity with temperature is observed with strongly broadened curves in all cases, however, a non Curie-Weiss behavior above the transition temperature is observed. The diffuseness coefficient (δdL) was calculated using Isupovs relation and by a more realistic model assuming a Gaussian distribution for the transition temperatures, in a temperature interval around the maximum permittivity temperature. The conditions under which each expression can be used are discussed.

Dielectric and structural properties of PST films deposited by RF ion sputtering on LSCO/Si substrates

Pb0.5Sr0.5TiO3 (PST) films have been obtained by RF ion sputtering on (La0.5Sr0.5)CoO3 substrates (LSCO). The purpose of this work is to investigate the relation between the crystalline structure and the dielectric properties of PST films grown on LSCO electrodes. PST films were deposited at 400°C in a fixed argon/oxygen (50/50) atmosphere. After deposition, PST films were post-annealed at different temperatures. Scanning Electron Microscopy (SEM) and X-Ray Diffraction were used for the structural studies. Crystallinity and surface morphology revealed a strong dependence on the crystallization conditions. The dielectric properties of the Pt/PST/LSCO/Si films were characterized through Capacitance (C) vs. Voltage (V) curves, Polarization (P) vs. Electric Field (E) curves and Current (I) vs Voltage (V) measurements. Leakage currents were also evaluated at each postannealing temperature.

Formation of the La0.03Sr0.255Ba0.7Nb2–yTiyO6–y/2 ferroelectric ceramic system

The study of the formation of the Sr0.255La0.03Ba0.7Nb2 − yTiyO6 − y/2 ferroelectric ceramic system and the influence of the sintering conditions and titanium concentration on the densification process is reported. A single-phase compound is observed for low titanium content (y ≤ 0.1) in the XRD spectra, being isostructural with the tetragonal tungsten bronze SBN phase. For high titanium concentrations (y > 0.1) the XRD patterns show, besides the tetragonal phase reflections, several small peaks evidencing an additional phase in the compound. This second phase was identified as isostructural to hexagonal Ba6Nb9Ti7O42. The grain size shows a linear increase with titanium content in the region of monophasic compositions and a possible liquid phase aided sintering process is analyzed.

Lead deficient PST Thin Films on LSCO/SrTiO3 by RF-Sputtering

We have investigated the structural, chemical and electrical properties of films with Pb 0.6 Sr 0.4 TiO 3 (PST60) nominal composition grown on well texturized LSCO/SrTiO 3 (STO) substrates by RF-Sputtering. The crystal structure and electrical properties of the PST60 films are remarkably influenced by the texture characteristics of the LSCO films. The structural and ferroelectric characteristics of PST60 thin films are determined to evaluate the potential of this heterostructure for non-volatile memory applications. Epitaxy of LSCO films was confirmed before depositing PST60 films on the above mentioned substrates through 4-Circle X-Ray Diffraction analysis (θ/2θ, ω and φ scans). The XRD analysis performed on the ferroelectric PST60 layer showed that the films are textured and entirely perovskite phase. LSCO and PST60, crystallize in the perovskite structure and their lattice parameters are well matched. This fact renders favorable structural and chemical conditions for the growth of PST60 on LSCO. The electrical performance of the Pt/PST60/LSCO/SrTiO 3 (001) capacitors was evaluated through Polarization-Voltage (P-V), Current-Voltage (I-V) and Fatigue measurements.