Effects of Y3+ doping on the microstructure evolution, optical, dielectric, and non-Ohmic properties of Na1/3Cd1/3Bi1/3Cu3Ti4O12 ceramics

Abstract

In this study, Na_1/3Cd_1/3(Bi_1-xY_x)_1/3Cu₃Ti₄O₁₂ (NCBYCTO, x = 0−0.20) ceramics were successfully prepared via solid state method. Their microstructure along with the optical, dielectric, and non-Ohmic properties were investigated systemically. It was shown that Y³⁺ doping caused the decrease in cation vacancy concentration and the increase in optical energy band. With the increase of Y³⁺ content, ceramics exhibited a more stable structure, while their average grain size increased from 6.80 μm to 9.12 μm and then decreased to 2.17 μm with the dopant amount. The relative density increased from 94.7 % for the undoped specimen to 95.6 % for the specimen with x = 0.20. The giant dielectric constant (ɛ′ = 44200) at a relatively low dielectric loss (tanδ = 0.048) at 10 kHz was obtained in the specimen with x = 0.08, being more than three times that of undoped sample and demonstrating the outstanding frequency stability in the range of 40−10⁶ Hz. The giant dielectric constant below 10⁶ Hz originated from Maxwell–Wagner relaxation related to the insulating grain boundaries (GBs) and followed the internal barrier layer capacitor model. Besides that, Y³⁺ doping improved the nonlinearity properties of NCBYCTO ceramics. The specimen with x = 0.20 had the largest nonlinearity coefficient α (∼9.60) and breakdown field strength E_b (∼7.15 kV/cm). At last, the nonlinear J-E characteristics were closely related to the GB conductivity activation energy.