Role of Domain Orientations in Forming the Hydrostatic Performance of Novel 2–2 Single Crystal/Polymer Composites

This paper reports results of a detailed study of the effects of the crystallographic orientation on the performance of the 2–2 parallel-connected composites based on relaxor-ferroelectric single crystals of 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3. These single crystals are poled along one of the following directions in the perovskite unit cell: [111] (single-domain state), [001] and [011] (polydomain states). The effect of the orientation of the main crystallographic axes in the single-crystal component on the hydrostatic piezoelectric coefficients d* h , e* h and g* h , squared hydrostatic figure of merit d* h g* h and hydrostatic electromechanical coupling factor k* h of the composites is studied for three cases of the poling direction of 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3. Maximum values of the hydrostatic parameters in the 2–2 0.72Pb(Mg1/3Nb2/3)O3-0.28PbTiO3 / polyvinylidene fluoride composites are d* h = 372 pC / N, g* h = 284 mV.m/N, d* h g* h = 33.8.10−12 Pa−1, and k* h = 0.361 (in the presence of the [011]-poled single crystal), and e* h = 45.1 C/m2 (in the presence of the [111]-poled single crystal). The inequality k*33/|k*3j | ≥ 5 (j = 1 and 2) is valid for the composite based on the [111]-poled single crystal under specific conditions. The composites exhibit remarkable properties, and the elastic and piezoelectric anisotropy of the single-crystal component (either [111]- or [011]-poled) plays an important role in achieving the large hydrostatic parameters.