Interrelationship between phase transition characteristics and piezoelectric response in lead lanthanum zirconate titanate relaxor ceramics

Dielectric and piezoelectric responses are investigated in relaxor-like lanthanum-modified lead zirconate titanate (PLZT) ceramics, for a La/Zr/Ti ratio of x/60/40 (x = 8 and 10 at.%), obtained by the conventional ceramic method. No significant differences were observed from the room temperature ferroelectric properties, for both PLZT compositions. On the other hand, from evaluation of the nonlinear dielectric response in terms of the Rayleigh’s model, a typical ‘soft’ behaviour is achieved in both materials, although the increments of the dielectric losses are slightly higher than the predicted by this model. The piezoelectric coefficient shows a remarkable increment with the applied dynamics stress, nevertheless without noticeable differences as a function of the lanthanum concentration. However, a significant difference is displayed in the weak-field direct longitudinal piezoelectric response. The dielectric properties revealed a higher diffuseness degree of the phase transition for the highest lanthanum content composition (PLZT 10/60/40). Thus, the observed difference in the piezoelectric response is discussed based on the nature of the phase transition in the studied relaxor materials.Postprint (published version

Interrelationship between phase transition characteristics and piezoelectric response in lead lanthanum zirconate titanate relaxor ceramics

Dielectric and piezoelectric responses are investigated in relaxor-like lanthanum-modified lead zirconate titanate (PLZT) ceramics, for a La/Zr/Ti ratio of x/60/40 (x = 8 and 10 at.%), obtained by the conventional ceramic method. No significant differences were observed from the room temperature ferroelectric properties, for both PLZT compositions. On the other hand, from evaluation of the nonlinear dielectric response in terms of the Rayleigh’s model, a typical ‘soft’ behaviour is achieved in both materials, although the increments of the dielectric losses are slightly higher than the predicted by this model. The piezoelectric coefficient shows a remarkable increment with the applied dynamics stress, nevertheless without noticeable differences as a function of the lanthanum concentration. However, a significant difference is displayed in the weak-field direct longitudinal piezoelectric response. The dielectric properties revealed a higher diffuseness degree of the phase transition for the highest lanthanum content composition (PLZT 10/60/40). Thus, the observed difference in the piezoelectric response is discussed based on the nature of the phase transition in the studied relaxor materials

BiFeO3 codoping with Ba, La and Ti: Magnetic and structural studies

"Conventional solid state reaction method, from oxides and carbonates, was employed to prepare bismuth (Bi)-based multiferroic systems. The undoped BiFeO3 (BFO) and the codoped system with Ba, La and Ti (Bi1?xBaxFe1?yTiyO3, Bi1?x?zBaxLazFe1?yTiyO3) with x,y,z=0.1 were prepared stoichiometrically and sintered at two different temperatures. The structural and magnetic properties were investigated at room temperature. XRD measurements confirm the obtaining of the rhombohedral perovskite structure of the BFO family system. For the undoped system, some reflections of undesired phases are present for two different sintering temperatures, while for the doped system only one phase is present for both temperatures. The magnetic characterization at room temperature revealed remarkable differences between the ceramic samples. The results show that for undoped BFO system, spontaneous magnetization is not observed at room temperature. Nevertheless, in doped one, a well-defined ferromagnetic behavior is observed at room temperature, possible, due to the suppression of the spatially modulated spin structure of BFO promoted by the reduction of the rhombohedral distortion and the weakening of the Bi–O bonds. The XPS results confirm the presence of oxygen vacancies and the coexistence of Fe3+ and Fe2+ in all the studied samples. Calorimetric measurements reveal that the dopant incorporation has not a direct effect in Néel temperature but possibly yes in ferroelectric-paraelectric transition.

Propiedades magnéticas y distribución de tamaños de nanopartículas de magnetita recubiertas con ácido oleico

"The particle size and particle size distribution are very important to biomedical applications because the uptake of nanoparticles is strongly dependent on particle size. Oleic acid coated magnetite nanoparticles were synthesized by using chemical co-precipitation. The average particle size and particle size distribution measured by different techniques are compared. The crystallite sizes estimated by X-Ray Diffraction (9.32 nm) and the average particle size calculated by Transmission Electron Microscopy (9.46 nm) are very similar. Atomic Force Microscopy revealed an average diameter of 1030 nm, which is bigger than estimated by other techniques due to the oleic acid layer covering the nanoparticles. The distribution of magnetic sizes of nanoparticles was also estimated through the magnetic response of the system, using the Langevin model (9.11 nm). Anisotropy constant (Ka = 4.74 *105 erg/cm3) and blocking temperature (TB = 118 K) were obtained.