Ellipsoids, characterizing the area of the admissible values of piezoelectric moduli , , and ( ) at the dielectric and elastic parameters' values listed in Table I for some orthorhombic crystals: (a) KNbO3 and (b) 0.27PIN-0.40PMN-0.33PT (single-domain crystals); (c) BaTiO3 and (d) PbTiO3 (tetragonal crystals with laminate 90° domain structure); (e) PMN-0.28PT and (f) PZN-0.07PT (rhombohedral polydomain crystals, poled along the  direction of the prototype cubic cell). Crosses mark the experimental points.
Ellipses, limiting the areas of the admissible values of piezoelectric moduli and ( ) for KNbO3 crystal at different values of piezoelectric modulus : 1 – , 2 – (experimental value) and 3 – . Cross marks the experimental point.
The components of relative permittivity (at fixed stress), elastic compliance (at fixed electric field), and piezoelectric moduli for single-domain KNbO3 and 0.27PIN-0.40PMN-0.33PT (PIN-PMN-PT) crystals (experimental data 15,16 ), BaTiO3 and PbTiO3 crystals with laminate 90° domain structure (calculated from the experimental data 18 using the formulas (2) ) and polydomain PMN-0.28PT and PZN-0.07PT crystals poled along the  direction (experimental data 22,23 ).
Transverse PR and , as well as and ratios calculated using the data of Table I .
The main parameters of the ellipsoids shown in Fig. 1 : aspect ratios a/b, a/c, limiting values of piezoelectric moduli , lying on the semi-major axis (a) at the maximal distance from the center, as well as the angles , , , characterizing orientation of the ellipsoid in three dimensional space , , .
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