The Ferroelectric and Piezoelectric Properties on Li$_{2}$O-excess (Na$_{0.51}$K$_{0.47}$Li$_{0.02}$)(Nb$_{0.8}$Ta$_{0.2}$)O$_{3}$ Ceramics

Abstract

One mol% Li$_{2}$O excess ($Na_{0.51}K_{0.47}Li_{0.02}$)($Nb_{0.8}Ta_{0.2}$)O$_{3}$ lead free piezoelectric ceramics were prepared by using a conventional mixed oxide method. Adding various additives such as Li$_{2}$CO$_{3}$, and Ta$_{2}$O$_{5}$, to (Na,K)NbO$_{3}$ makes it easy to carry out the sintering and the poling processes of pure (Na,K)NbO$_{3}$ which has difficulty in sintering and poling. Also, 1 mol% Li$_{2}$O excess $Na_{0.51}K_{0.47}Li_{0.02}$)($Nb_{0.8}Ta_{0.2}$)O$_{3}$ has a lower sintering temperature than that of pure (Na,K)NbO$_{3}$. The crystal structures of 1-mol% Li$_{2}$O-excess ($Na_{0.51}K_{0.47}Li_{0.02}$)($Nb_{0.8}Ta_{0.2}$)O$_{3}$ lead-free piezoelectric ceramics were examined for several sintering temperatures (950 – 1200 ${^{\circ}C}$) by using X-ray diffraction analysis. A piezoelectric constant and a planar electromechanical coupling coefficient of 231 pC/N and 38.9 % were measured in the 1-mol % Li$_{2}$O-excess ($Na_{0.51}K_{0.47}Li_{0.02}$)($Nb_{0.8}Ta_{0.2}$)O$_{3}$ lead-free piezoelectric ceramics sintered at 1050 ${^{\circ}C}$. Also, the remnant polarization and the coercive electric field were 10 $\mu$C/cm$^{2}$ and 4 kV/cm for NKN-LT ceramics, respectively. By measuring the temperature dependent dielectric constant, we found that the tetragonal-cubic phase transition temperature (T$_{c}$) of 1-mol % Li$_{2}$O-excess ($Na_{0.51}K_{0.47}Li_{0.02}$)($Nb_{0.8}Ta_{0.2}$)O$_{3}$ ceramics sintered at 1050 ${^{\circ}C}$ was around 346.8 ${^{\circ}C}$.

Keywords

• Lead-free piezoelectric;
• Ferroelectrics