Effect of Molecular Mass of B-site Ions on Electromechanical Coupling Factors of Lead-Based Perovskite Piezoelectric Materials

The effects of the molecular mass of B-site ions of Pb(B^'B^'')O₃–PbTiO₃ (B^'=Mg, Zn, Ni, Sc, In and Yb; B^''=Nb and Ta) and Pb(B, Ti)O₃ (B=Zr, Hf and Sn) piezoelectric materials on the electromechanical coupling factors were investigated. The relationship between the electromechanical coupling factor k_p near a morphotropic phase boundary (MPB) and the molecular mass of B-site ions is systematically discussed. The reason why k_p of Pb(Zr, Ti)O₃ (PZT) is larger than that of Pb(Hf, Ti)O₃ (PHT) or Pb(Sn, Ti)O₃ (PST) is explained in terms of the molecular mass difference between A-site and B-site ions of Pb(B, Ti)O₃. It may be concluded that a combination of the B-site ions which have a lower molecular mass in MPB composition, play an important role in realizing large electromechanical coupling factors in lead-based perovskites. From this viewpoint, MPB compositions of Pb[(Sc_1/2Nb_1/2)_0.58Ti_0.42]O₃ (PSNT 58/42), which has the largest molecular mass difference between A-site and B-site (Amass-Bmass=147.1) ions may be the best combinations of all Pb(B^'B^'')O₃–PbTiO₃ and Pb(B, Ti)O₃ systems so far reported. However, if Pb[(Al_1/2Nb_1/2)_1-xTi_x]O₃ and Pb[(Ga_1/2Nb_1/2)_1-xTi_x]O₃ systems can be synthesized into pure perovskite structures near the MPB, a better piezoelectric performance than PZT 53/47 or PSNT 58/42 is expected.