Investigations On Fabrication And Properties Of Multifunctional Ceramics With Piezoelectricity And Photoluminescence

In recent years, much attention has been paid to develop the multifunctional single-phase materials. Two functional effects of piezoelectricity and the photoluminescence have important applications in sensors, transducers, optical waveguides and display devices. However, coupling effects between these two effects have been seldom studied until now. In present work, bases on the lead-free piezoelectric ceramics (1-x)(Bi0.5Na0.5)Ti03-xBaTi03with the composition around the morphotropic phase boundary (MPB), we introduced rare earth ions and studied the relations among the compositions, temperature, electric field and the phase structure, dielectric, ferroelectric, piezoelectric and optical properties. The main results in this dissertation are as follows:1. Through doping different kinds of rare earth ions, we observed strong photoluminescence effects in the lead-free piezoelectric O.935(Bi0.5Na0.5) TiO3-0.065BaTiO3:Re (BNT-6.5BT:Re, Re=Pr. Eu, Gd, Dy) ceramics. The strong red emission (610nm) has been observed in the BNT-6.5BT:Pr ceramic. The emission wavelengths of the BNT-6.5BT:Eu ceramic located around572nm and615nm, respectively. In addition, the doped ceramics exhibited better electric properties than the pure one. Compared with the pure BNT-6.5BT ceramic, the remnant polarization of the BNT-6.5BT:Dy ceramic can increase to41.8μ-C/cm2with a coercive field2.2kV/mm. The piezoelectric constant of BNT-6.5BT:Pr can reach up to-180pC/Nwithelectromechanical coupling coefficient kt-0.5and kp-0.3.2.Lead-free piezoelectric0.93(Bi0.5Na0.5)Ti03-0.07BaTi03:xPr (BNT-7BT: xPr,.v=0.0.001,0.003,0.005,0.007,0.008,0.010) ceramics have been fabricated through doping Pr3+ions with different concentration into the0.97(Bi0.5Na0.5) TiO3-0.03BaTiO3ceramics. A large strain of0.35%-0.40%(Smax/Emax=724-750pm/V) at a low driving field ranging from4.6-5.5kV/mm was obtained at a critical composition of BNT-7BT:0.008Pr at room temperature. It is worth noting that the value of Smax/Emax is the highest one among the lead-free BNT-based piezoelectric ceramics until now, which is attributed to the transformation from pseudocubic short-range-order to ferroelectric long-range-order induced by the external electric field. In addition, the unpolarized BNT-7BT:0.005Pr ceramic had the strongest red photoluminescence emission intensity. On the other hand, the most significant modulation of intensity was detected in the BNT-7BT.0.003Pr ceramic after poled under different electric fields. An enhancement of40%was observed under a poling electric field of3kV/mm in the BNT-7BT:0.003Pr ceramic. The result shows that the poling electric field can effectively control the emission intensity and ferroelectric polarization provides a new way to modulate the photoluminescence effect.