Practical High Piezoelectricity in Barium Titanate Ceramics Utilizing Multiphase Convergence with Broad Structural Flexibility

Abstract

Due to growing environmental concerns on the toxicity of lead-based piezoelectric materials, lead-free alternatives are urgently required but so far have not been able to reach competitive performance. Here we employ a novel phase-boundary engineering strategy utilizing the multiphase convergence, which induces a broad structural flexibility in a wide phase-boundary zone with contiguous polymorphic phase transitions. We achieve an ultrahigh piezoelectric constant (d 33) of 700 ± 30 pC/N in BaTiO3-based ceramics, maintaining >600 pC/N over a wide composition range. Atomic resolution polarization mapping by Z-contrast imaging reveals the coexistence of three ferroelectric phases (T + O + R) at the nanoscale with nanoscale polarization rotation between them. Theoretical simulations confirm greatly reduced energy barriers facilitating polarization rotation. Our lead-free material exceeds the performance of the majority of lead-based systems (including the benchmark PZT-5H) in the temperature range of 10–40 °C, making it suitable as a lead-free replacement in practical applications. This work offers a new paradigm for designing lead-free functional materials with superior electromechanical properties.

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 …”

“…After this work, intensive investigations associated with phase boundaries formation and piezoelectricity improvement have been performed in BT‐based ceramics via chemical modification. In 2018, our group developed a new phase boundary strategy in a designed (1‐ x )Ba(Ti 0.89 Sn 0.11 )O 3 ‐ x (Ba 0.7 Ca 0.3 )TiO 3 (BTS 0.11 ‐ x BCT) system 72 . The left terminal is Ba(Ti 0.89 Sn 0.11 )O 3 with quasi‐quadruple point comprising R, O, T, and C phases at ~40°C, and the right terminal is (Ba 0.7 Ca 0.3 )TiO 3 which can facilitate the stability of ferroelectric phases.…”

“…C, Temperature dependence of d 33 and P r for BTZ‐0.5BCT 91,99 . D, Phase diagram of (1– x )Ba(Ti 0.89 Sn 0.11 )O 3 ‐ x (Ba 0.7 Ca 0.3 )TiO 3 (BTS 0.11 ‐ x BCT) ceramics 72 . E, Distribution of d 33 in temperature‐composition plane for BTS 0.11 ‐ x BCT 72 .…”