Structural perspective on the anomalous weak-field piezoelectric response at the polymorphic phase boundaries of (Ba,Ca)(Ti,M)O3

Abstract

Although, as part of a general phenomenon, the piezoelectric response of Ba(Ti 1-y M y )O 3 (M= Zr, Sn, Hf) increases in the vicinity of the orthorhombic (Amm2) -tetragonal (P4mm) and orthorhombic (Amm2)-rhombohedral (R3m) polymorphic phase boundaries, experiments in the last few years have shown that the same phase boundaries show significantly enhanced weakfield piezo-properties in the Ca-modified variants of these ferroelectric alloys, i.e., (Ba,Ca)(Ti, M)O 3 . So far there is a lack of clarity with regard to the unique feature(s) which Ca modification brings about that enables this significant enhancement. Here, we examine this issue from a structural standpoint with M = Sn as a case study. We carried out a comprehensive comparative structural, ferroelectric and piezoelectric analysis of the Amm2 phase in the immediate vicinity of the P4mm -Amm2 phase boundaries of (i) Ca-modified Ba(Ti,Sn)O 3 , as per the nominal formula (1-x)BaTi 0.88 Sn 0.12 O 3 -(x)Ba 0.7 Ca 0.3 TiO 3 and (ii) without Ca modification, i.e. Ba(Ti 1-y Sn y )O 3 . We found that the spontaneous lattice strain of the Amm2 phase is noticieably smaller in the Ca-modified counterpart. Interestingly, this happens alongwith an improved spontaneous polarization by enhancing the covalent character of the Ti-O bond.Our study suggests that the unique role of Ca-modification lies in its ability to induce these seemingly contrasting features (reduction in spontaneous lattice strain but increase the polarization). *

Multifunctional barium titanate ceramics via chemical modification tuning phase structure

“…Type II: E, Evolution of ε r ‐ T curves in typically aliovalent cation doped BT ceramics at A site 22,51,58‐62 . Type I of B‐site substitution: F and G, ε r ‐ T curves showing T R‐O , T O‐T , and T C evolutions in BT ceramics by Zr 4+ , Hf 4+ , or Sn 4+ substitution 21,54,68‐73 . H, The corresponding phase diagram.…”

“…into A site not only decrease T R‐O , T O‐T , and T C but also damage ferroelectric phase, causing the diffusion of ferroelectric‐paraelectric phase transition (Type 2, Figure 2E2). 58‐62 For B (Ti 4+ )‐site substitution, the most utilized cations are valence‐stable Zr 4+ , 21,54,67‐69 Hf 4+ , 68‐70 and Sn 4+ , 68,69,71‐73 which show similar ionic radii and same valence with Ti 4+ . As displayed in Figure 2F,G, introducing Zr 4+ , Hf 4+ or Sn 4+ to B site shifts T R‐O and T O‐T to high temperature and simultaneously decreases T C of BT ceramics, therein T R‐O moves faster than T O‐T .…”

“…B‐D, Schematics of constructing O‐T, R‐(O)‐T, and R‐O phase boundaries at RT through shifting T R‐O and T O‐T by chemical substitution. E, Shifting speed of A‐site Ca 2+ , B‐site Zr 4+ , Hf 4+ or Sn 4+ substitution on T R‐O , T O‐T , and T C of BT ceramics 21,54,55,68‐73 . F, Phase diagram of A‐site Ca 2+ and B‐site Zr 4+ co‐doped BT‐based ceramics 21,54,67‐69 …”

“…Hence, the proposed tricritical point in BTZ‐ x BCT is actually a four‐phase pinched point (quasi‐quadruple point) among R, O, T and C phases. And the intermediate O phase is proposed to play an important role on the enhancement of piezoelectricity 73,90,91,95‐98 . On the other hand, it is impossible for BT‐based ceramics to achieve a real MPB containing nearly parallel boundaries along temperature axis as in PZT‐based ceramics due to the nature of polymorphic phase boundary in BT.…”

Defect engineering electrical properties of lead‐free potassium sodium niobate‐based ceramics

“…Rietveld refinement has been proved to be an effective method to analyze the phase structure. 20 In this work, Rietveld refinements of ceramic powders with x = −0.01, 0, and 0.01 were carried out, as shown in Figure 3A-C. The detailed Rietveld refinement results can be seen in Table 1.…”