Anisotropy of electromechanical properties and hydrostatic response of advanced 2–2‐type composites

The paper reports results on the high performance of novel piezo‐active composites based on relaxor‐ferroelectric single crystals (SCs) of x Pb(In 0.5 Nb 0.5 )O 3 – y Pb(Mg 1/3 Nb 2/3 )O 3 –(1 −  x  −  y )PbTiO 3 . We present a comparative analysis of the electromechanical properties of 2–2‐type composites based on single‐domain SCs from symmetry classes 3 m and mm 2. The parallel connection of the layers, the presence of an auxetic polymer component and the appropriate orientation of the main crystallographic axes of the single‐crystal layers lead to the development of large piezoelectric anisotropy and considerable hydrostatic piezoelectric response in comparison to the single‐crystal component. Effective piezoelectric coefficients $d_{3j}^{*} $ and electromechanical coupling factors $k_{3j}^{*} $ of the composites obey the conditions $d_{33}^{*} $ /| $d_{31}^{*} $ | ≥ 10, $d_{33}^{*} $ /| $d_{32}^{*} $ | ≥ 10, $k_{33}^{*} $ /| $k_{31}^{*} $ | ≥ 10, and $k_{33}^{*} $ /| $k_{32}^{*} $ | ≥ 10 at $k_{33}^{*} $  ≈ 0.6. Hydrostatic piezoelectric coefficients $d_{{\rm h}}^{*} $  ≈ 470 pC/N and $g_{{\rm h}}^{*} $  ∼ (10 2 –10 3 ) mV m/N are one to two orders‐of‐magnitude larger than those of the single‐crystal component, which make it attractive for various piezotechnical applications. The role of the elastic properties of the components is discussed in connection with the large hydrostatic parameters.