Photoluminescence and temperature dependent electrical properties of er-doped 0.94 Bi _0.5 Na _0.5 TiO ₃-0.06 BaTiO ₃ ceramics

Er-doped 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNT-6BT: xEr, x is the molar ratio of Er³⁺ doping) lead-free piezoceramics with x = 0-0.02 were prepared and their multifunctional properties have been comprehensively investigated. Our results show that Er-doping has significant effects on morphology of grain, photoluminescence, dielectric, and ferroelectric properties of the ceramics. At room temperature, the green (550 nm) and red (670 nm) emissions are enhanced by Er-doping, reaching the strongest emission intensity when x = 0.0075. The complex and composition-dependent effects of electric poling on photoluminescence also have been measured. As for electrical properties, on the one hand, Er-doping tends to flatten the dielectric constant-temperature (ε_r-T) curves, leading to temperature-insensitive dielectric constant in a wide temperature range (50°C-300°C). On the other hand, Er-doping significantly decreases the ferroelectric-relaxor transition temperature (T_F-R) and depolarization temperature (T_d), with the T_F-R decreasing from 76°C to 42°C for x = 0-0.02. As a result, significant composition-dependent electrical features were found in ferroelectric and piezoelectric properties at room temperature. In general, piezoelectric and ferroelectric properties tend to become weaker, as confirmed by the composition-dependent piezoelectric coefficient (d₃₃), planar coupling factor (k_p), and the shape of polarization-electric field (P-E), current-electric field (J-E), bipolar/unipolar strain-electric field (S-E) curves. Furthermore, to understand the relationship between the T_F-R/T_d and the electrical properties, the composition of x = 0.0075 has been intensively studied. Our results indicate that the BNT-6BT: xEr with appropriate Er-doping may be a promising multifunctional material with integrated photoluminescence and electrical properties for practical applications.