Terminology

According to general practice, the 3rd axis is parallel to the polarisation direction and the 1st and 2nd axes are perpendicular to this, as shown in the figure. The various coefficients are numbered with a notation of 2 indices, the first one describing electrical effects and the second one mechanical effects. Examples are given below.

K3S  K1T K: Dielectric constant (e3S/e0) 3: Electrodes are perpendicular to 3rd axis (direction of polarisation) S: All strains in the material are constant (e.g., mechanical deformation is blocked in any direction, "clamped") K: Dielectric constant (e1T/e0) 1: Electrodes are perpendicular to 1st axis T: All stresses on material are constant (e.g., no external forces) kp   k15 k: Electromechanical coupling factor p: Stress or strain is equal in all directions perpendicular to 3rd axis; electrodes are perpendicular to 3rd axis; used only for ceramics k: Electromechanical coupling factor 1: Electrodes are perpendicular to 1st axis 5: Stress or strain is in shear form around 2nd axis dh  d33 d: Piezoelectric charge coefficient h: Hydrostatic stress is applied equally in all directions; electrodes are perpendicular to 3rd axis (ceramics) d: Piezoelectric charge coefficient 3: Electrodes are perpendicular to 3rd axis 3: Applied stress or piezoelectrically induced strain is in '3' direction g15  g31 g: Piezoelectric voltage coefficient 1: Electrodes are perpendicular to 1st axis 5: Applied stress or piezoelectrically induced strain is in shear form around 2nd axis g: Piezoelectric voltage coefficient 3: Electrodes are perpendicular to 3rd axis 1: Applied stress or piezoelectrically induced strain is in '1' direction s36E  s11D s: Elastic compliance 3: Strain or stress is in '3' direction 6: Stress or strain is shear around '3' direction E: Compliance is measured with closed circuit s: Elastic compliance 1: Strain or stress is in '1' direction 1: Stress or strain is in '1' direction D: Compliance is measured with open circuit

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