Piezoceramics properties as a function of the structure in the system (K,Na,Li)(Nb,Ta,Sb)O3

The influence of the sintering conditions and stoichiometry on the crystalline symmetry and electrical properties of the system (K_0.44+xNa_0.52Li_0.04)(Nb_0.86Ta_0.10Sb_0.04)O_3+x/2, with x = -0.06, 0.00, and 0.04, has been evaluated. By lowering the concentration of K cations, a faster stabilization of the tetragonal phase is reached. Increasing the sintering time also leads to the stabilization of the tetragonal phase at room temperature, as evidenced by Raman spectroscopy, thus improving the piezoelectric properties of these materials. The Raman spectra versus temperature showed 2 anomalies at temperatures of ~70 and ~270 to 330degC, associated with polymorphism and the ferro-paraelectric phase transitions, respectively. Active Raman scattering modes are observed above Curie temperature, indicating that the symmetry is not cubic but pseudocubic. This pseudocubic phase is associated with relaxor diffuseness, attributed to composition fluctuations. In addition, the piezoelectric properties were correlated with the tetragonality of the system, showing a linear dependence between the piezoelectric properties and the tetragonality ratio. The ceramics with c/a = 1.011 ratio exhibit enhanced electrical properties, d₃₃ ~255 pC/N and k_p ~0.47.