Grain size-driven effect on the functional properties in Ba0.6Sr0.4TiO3 ceramics consolidated by spark plasma sintering

Influence of Grain Size on Dielectric Behavior in Lead-Free 0.5 Ba(Zr0.2Ti0.8)O3–0.5 (Ba0.7Ca0.3)TiO3 Ceramics

“…However, it is worth mentioning that the "silent" [E(TO) + E(LO) + B 1 ] mode located at 294 cm −1 and, especially, the [A 1 (TO) + E(LO)] mode at 181 cm −1 , are more visible than those corresponding to the submicron-structured SG-CS sample, which seems to suggest that the residual polar order above the Curie temperature is more stable as the grain size decreases toward the nanometer scale. This behavior was also reported for the fine-grained Ba 0.6 Sr 0.4 TiO 3 ceramics, which at room temperature are found in the paraelectric state [36] and supports the hypothesis of an enhancement of a relaxor-like behavior determined by a particular structure of the grains, which consist of a non-polar, cubic matrix in which polar nanoregions (PNR) are randomly distributed. Complex distortions may arise in these polar nanoclusters, i.e., tetragonal, orthorhombic, or rhombohedral.…”

“…An increase in the unit cell volume of the major orthorhombic polymorph was found with decreasing grain size. This trend of the unit cell volume expansion was also observed in the (Ba0.6Sr0.4)TiO3 ceramics when the grain size dropped from the submicron toward the nanometer range [36]. The prevalence at room temperature of the orthorhombic form in the conventionally sintered, coarser samples is in good agreement with the recently revised The XRD maxima of the SG-SPS sample present bell-shaped profiles and reduced intensity, characteristic of a shorter-range crystalline order induced by the nanostructure, compared to the Lorentzian maxima specific to the long-range order identified in the other 2 coarser SS-CS and SG-CS samples.…”

“…An increase in the unit cell volume of the major orthorhombic polymorph was found with decreasing grain size. This trend of the unit cell volume expansion was also observed in the (Ba 0.6 Sr 0.4 )TiO 3 ceramics when the grain size dropped from the submicron toward the nanometer range [36]. The prevalence at room temperature of the orthorhombic form in the conventionally sintered, coarser samples is in good agreement with the recently revised phase diagram of the BCT-BTZ system, which shows an intermediate compositional range corresponding to the orthorhombic polymorph, placed between the ranges associated with the rhombohedral and tetragonal phase, respectively [7,8].…”

“…04-006-8930) and orthorhombic BaTi 2 O 5 (ICDD no. 04-017-1818) were identified at the detection limit of the diffractometer as residual phase in SG-CS and SG-SPS ceramics, frequently reported in the literature for the sol-gel synthesis [36].…”

“…The influence of grain size down-scaling towards the submicron and nanometer range on electrical properties was intensively studied mostly in undoped BaTiO 3 bulk ceramics [29][30][31][32][33] and in some of the homovalent solid solutions such as (Ba,Sr)TiO 3 [34][35][36] and Ba(Ti,Zr)O 3 [37]. It was shown that specific features such as reduced and frozen polarization, flattening of the permittivity-temperature (ε(T)) maximum, reduction of both Curie temperature and dielectric constant to ~1000, and non-hysteretic permittivity-field (ε(E)) dependence and high tunability, all originating from complex stress-induced structural distortions associated with the dramatic drop of grain size, fulfill the requirements imposed for microwave devices [28][29][30][31][32][33][34][35][36]. A systematic study regarding the influence of the structuring level on the dielectric behavior of the BCTZ ceramics, when the grains cover a wide range of sizes, from tens of microns to tens of nanometers, has not yet been reported.…”