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[(Sc1/2Nb1/2)0.58Ti0.42]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[(Al1/2Nb1/2)1-x Ti x ]O3 and Pb[(Ga1/2Nb1/2)1-x Ti 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.