Importance of the crystalline symmetry in the piezoelectric properties   of (K0.44+xNa0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3+x/2 lead-free ceramics
  Lead-free ceramics (K0.44+xNa0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3+x/2 (x=-0,06) were prepared by conventional solid state sintering. The results indicate a correlation between crystalline symmetry and electrical properties. Higher tetragonality was observed in samples with higher piezoelectric response. As the tetragonality increase the presence of polymorphic phase decrease associated with a reduction of the relaxor behaviour response. The ceramics with c/a = 1.011 ratio exhibit enhanced electrical properties. The Raman spectroscopy showed a certain asymmetry in the paraelectric phase above the Curie temperature Tc that provokes retention of the polarization. The crystalline symmetry plays a crucial role in the piezoelectric properties of the system. 
F. Rubio-Marcos, P. Marchet, T. Merle-Mejean, J.F. Fernandez