Relaxor behavior in nanostructured Pb(Zn1/3Nb2/3)O3–Pb(Fe1/2Nb1/2)O3–PbTiO3 ceramics

Abstract

There is controversy about the persistence or not of the relaxor state in the nanoscale. We report here the dielectric properties of nanostructured ceramics of the Pb͑Zn 1/3 Nb 2/3 ͒O 3 -Pb͑Fe 1/2 Nb 1/2 ͒O 3 -PbTiO 3 ternary system with an average grain size of 20 nm, which clearly indicate that it persists as long as correlations among polar nanoregions are possible across grain boundaries. Two independent Vogel-Fulcher type relaxations are found in the materials that have a non-negligible width of the size distribution, which are proposed to be associated with intra-and intergranular correlations that show freezing at different temperatures. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3118527͔ Ferroelectric ͑FE͒ nanostructures are attracting a lot of attention from the microelectronic industry due to their potential applications in piezoelectric microelectromechanical systems and also for implementing sensing and actuation in nanoelectromechanical devices. 1 The feasibility of using FE nanostructured polycrystals in these miniaturized devices depends on how the properties scale with the decrease in crystal size. This has raised interest in the processing of ceramics with a nanometric grain size and in studying the effect of the grain size reduction on the macroscopic properties. Particularly, in perovskite ͑Pe͒ relaxor-FE solid solutions with morphotropic phase boundary. 2,3 Pb͑Mg 1/3 Nb 2/3 ͒O 3 -PbTiO 3 ͑PMN-PT͒ is one of these systems, for which an evolution from FE to relaxor-type behavior with decreasing grain size has been described. 2,3 In relaxor PMN, the disappearance of the dielectric relaxation below a critical grain size of 30 nm has been reported. 2,4 Pb͑Zn 1/3 Nb 2/3 ͒O 3 -PbTiO 3 ͑PZN-PT͒ is another example of such systems, which present the highest known piezoelectric coefficients. 5 However, Pe phase powders have only been obtained by high pressure synthesis or by mechanochemical activation. 6 Moreover, the processing of high-quality ceramics has not been accomplished due to the thermal decomposition of the Pe into a pyrochlore ͑Py͒ phase. 6 We recently succeeded in processing nanostructured ceramics of 0.92PZN-0.08PT with an average grain size of 20 nm by spark plasma sintering ͑SPS͒ of a powder obtained by mechanochemical activation. 7 SPS technique allows to obtain dense ceramics at moderate temperatures and short times, thus limiting grain growth. 8 In the case of PZN-PT, this is also advantageous for minimizing Pe thermal decomposition, and ceramics were obtained at 873 K. However, materials presented traces of Py due to the onset of Pe decomposition at 823 K. This prevented the temperature of the SPS to be further increased. The electrical properties of the nanostructured material were characterized and relaxor-type behavior was found. 9 In this work, we present results on the dielectric properties of similarly nanostructured materials with decreasing Py content up to its disappearance. This was achieved by adding Pb͑Fe 1/2 Nb 1/2 ͒O 3 ͑PFN͒ to the binary system, which enhance...

Nanostructuring Effects in Piezoelectric BiScO3–PbTiO3 Ceramics

“…Grain size effects have been detailed for related systems like Pb(Mg 1/3 Nb 2/3 )O 3 –PbTiO 3 and Pb(Zn 1/3 Nb 2/3 )O 3 –PbTiO 3 down to 15 nm . These relaxor‐based solid solutions also show ferroelectric MPBs between rhombohedral, monoclinic, and tetragonal polymorphs, and a size effect in the phases present at the MPB has been described .…”

“…These relaxor‐based solid solutions also show ferroelectric MPBs between rhombohedral, monoclinic, and tetragonal polymorphs, and a size effect in the phases present at the MPB has been described . However, this was not the primary cause of the size effects on properties but the slowing down of the kinetics of the ferroelectric‐to‐relaxor transition, until the final stabilization of the high‐temperature relaxor state for grain sizes of a few tens of nm …”

Spark Plasma Sintering as a Useful Technique to the Nanostructuration of Piezo‐Ferroelectric Materials

“…Similar results were obtained in the case of the Pb(Zn 1/3 Nb 2/3 )O 3 -Pb(Fe 1/2 Nb 1/2 )O 3 -PbTiO 3 system. [157] Fig. 24.…”

Ergodicity of fine‐grained canonical relaxor ferroelectric (Bi0.5Na0.5)1‐xBaxTiO3 films

“…It has been shown that the reduction in the grain size is related to the appearance of a slowing down of the kinetics of this relaxor‐to‐ferroelectric transition . For the smallest, nanometric grains, a stable relaxor state at room temperature is obtained …”