Anisotropic Piezoelectric Properties of Porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 Ceramics with Oriented Pores through TBA-Based Freeze-Casting Method

Abstract

Porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) piezoelectric ceramics with an oriented directional hole structure were prepared by using the tertbutyl alcohol (TBA)-based freeze-casting method. The influences of sintering temperatures on the microstructure and piezoelectric properties of porous BCZT ceramics were investigated both perpendicular and parallel to the freezing direction. With the increase in sintering temperatures and the porosities decreased from 58% to 42%, the compressive strength increased from 14.0 MPa to 25.0 MPa. In addition, the d33 value of 407 pC/N for the sample sintered at 1400 °C was obtained parallel to the freezing direction, which was 1.40 times that of the other direction.

Porosity effect on the functional properties and energy harvesting performance of Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics

“…38 The Ca 2+ ions with larger polarization than Ba 2+ ions might strengthen the interaction between A-and B-site ions, leading to the effective Ca 2+ ions occupying both Aand B-sites in the ABO 3 perovskite structure and inducing the long-range-order array of the lattice. 8,18,38 In Figure 4B (the dielectric loss vs. temperature), a more sensitive phase transition character of porous BCTZ ceramics could be observed. For the investigated samples, the dielectric loss versus temperature reveals two peaks of the phase transition at about 55 • C and about room temperature around 27 • C, which are related to two structural phase transitions: Tetragonal to Cubic (T T-C ) and Orthogonal to Tetragonal (T O-T ), respectively.…”

“…Previous works indicated an influence of porosity in inducing structural modifications in BaTiO 3 ceramics 19,24,25 and in its solid solutions. 8,26 In particular, BCTZ with nominal composition around MPB is expected to show phase coexistence, and the phase compositions are influenced by microstructural factors such as grain size and porosity level. The observed XRD patterns of the investigated BCTZ porous ceramics indeed show the coexistence of Orthorhombic (O, space group Amm2) and Tetragonal (T, space group P4mm) phases, but the presence of other polymorphs is not excluded (Figure 1A).…”

“…Therefore, using isostatic pressing of BCTZ powders simply mixed with PMMA polymer as a sacrificial template for generating porosity was demonstrated to be a simple and effective method to generate high piezoelectric responses with respect to other lead-free porous piezoelectrics. 8,[50][51][52][53][54][55] Since in the intermediate porosity range, the d 33 coefficient increases, while permittivity monotonically decreases in all the porosity ranges, the requirements for enhancing the piezoelectric FOM (FOM 33 ) may be fulfilled at the intermediate porosity level. In order to explore the capability of these porous BCTZ ceramics to be used for mechanical energy harvesting applications, the calculated piezoelectric FOM, according to relation (1) versus porosity (Figure 8B), reveals that the piezoelectric energy harvesting FOM 33 increases with increasing porosity until reaching the highest value of 18%.…”

“…Among them, (Ba,Ca)(Ti,Zr)O 3 solid solutions started to be, in the last years, the most studied Pb-free piezoelectric systems, together with other Pb-free piezoelectrics with valuable properties. 7,8 Dense electroceramics present superior dielectric, ferro-, piezo-, and pyroelectric responses, but recent studies demonstrated that introducing a certain porosity level is beneficial for improving a few types of properties. 1 For example, a permittivity reduction while preserving a high tunability induced by a small porosity in ferroelectric ceramics is useful in tunability applications.…”

“…I G U R E 8 (A) Comparison of d 33 of the porous BCZT ceramics with ones obtained for other lead-free porous piezoelectrics produced by other methods (refs. BT freeze casting50 ; BCTZ (BURPS)51 ; BCTZ (Freeze casting)8 ; NKNS (Freeze casting)52 ; BCZT (Freeze casting), BCZT (BURPS_PMMA), and BCZT (CNT)53 ; (B) piezoelectric energy harvesting figure of merit versus porosity level in porous BCTZ ceramics. F I G U R E 9 Comparison of the maximum voltage recovered with ones obtained for BaTiO 3 porous ceramics in similar conditions.…”