Piezoelectric Performance and Hydrostatic Parameters of Novel 2–2-Type Composites

This paper provides a detailed study of the structure—piezoelectric property relationships and the hydrostatic response of 2–2-Type composites based on relaxor-ferroelectric 0.72 Pb (Mg_1/3Nb_2/3)O₃–0.28PbTiO₃ single crystal (SC) material. Type I layers in the composite system are represented by a single-domain [111]-poled SC. Changes in the orientation of the crystallographic axes in the Type I layer are undertaken to determine the maximum values of the hydrostatic piezoelectric coefficients <inline-formula> <tex-math notation="LaTeX">$d_{h}^{\ast } $ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$g_{h}^{\ast } $ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$e_{h}^{\ast } $ </tex-math></inline-formula>, and squared figure of merit <inline-formula> <tex-math notation="LaTeX">$d_{h}^{\ast } g_{h}^{\ast } $ </tex-math></inline-formula> of the composite. The Type II layers are a 0–3 composite whereby inclusions of modified PbTiO₃ ceramic are distributed in a polymer matrix. A new effect is described for the first time due to the impact of anisotropic elastic properties of the Type II layers on the hydrostatic piezoelectric response that is coupled with the polarization orientation effect in the Type I layers. Large hydrostatic parameters <inline-formula> <tex-math notation="LaTeX">$g_{h}^{\ast } \approx 300$ </tex-math></inline-formula>–400 mV <inline-formula> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> m/N, <inline-formula> <tex-math notation="LaTeX">$e_{h}^{\ast } \approx 40$ </tex-math></inline-formula>–45 C/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{2}$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$d_{h}^{\ast } g_{h}^{\ast } \sim 10^{-11}$ </tex-math></inline-formula> Pa<inline-formula> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> are achieved in the composite based on the 0.72 Pb(Mg_1/3Nb_2/3)O₃–0.28PbTiO₃ SC. Examples of the large piezoelectric anisotropy (<inline-formula> <tex-math notation="LaTeX">$|d_{33}^{\ast } /d_{3f}^{\ast } | \ge 5$ </tex-math></inline-formula> or <inline-formula> <tex-math notation="LaTeX">$| g_{33}^{\ast } /g_{3f}^{\ast } | \ge 5$ </tex-math></inline-formula>) are discussed. The hydrostatic parameters of this novel compositesystem are compared to those of conventional 2–2 piezocomposites.