Significantly improved dielectric properties of TiO2 ceramics through acceptor-doping and Ar/H2 annealing

The acceptor-doped rutile TiO₂ ceramics, x mol% M₂O₃-(1-x) mol% TiO₂ (M = Al³⁺, Ga³⁺, and In³⁺), were prepared by solid state reaction method. The influence of Ar/H₂ annealing on the structural and dielectric properties of the ceramics were systematically investigated. Our results reveal that the dielectric properties of the ceramics can be significantly improved by the Ar/H₂ annealing. Ga³⁺ is found to be the most suitable dopant with the best doping level of 5 mol%. Excellent dielectric properties of colossal and flat dielectric permittivity (~1.2 × 10⁵ (@1 kHz and 25 °C), low dielectric loss (~0.1), and good frequency stability were achieved over the temperature range of -70–150 °C in the Ar/H₂-annealed 5 mol% Ga₂O₃-95 mol% TiO₂ ceramic. This approach of acceptor-doping and Ar/H₂ annealing leads to two thermally activated relaxations in the sample. The low-temperature relaxation is argued to be a Maxwell-Wagner relaxation caused by frozen electrons, while the high-temperature relaxation is a glass-transition-like relaxation associated with the freezing process of the electrons. This work highlights that engineering low-temperature Maxwell-Wagner relaxation paves a new way other than the frequently used acceptor-donor dual doping to design superior dielectric properties in the TiO₂ system.     

Characterization of crystal structure,electrical and electromechanical properties of Mg-doped 0.94Na1/2Bi1/2TiO3-0.06BaTiO3

The use of lead-free piezoelectric materials in high-power applications requires a high mechanical quality factor Q_m and temperature-stable ferroelectric properties. In this article, the influence of Mg-doping on the 0.94Na_1/2Bi_1/2TiO₃-0.06BaTiO₃ system is analysed with focus on the role of defects related to ferroelectric hardening. Temperature stability (depolarization temperature), electromechanical properties (piezoelectric activity, Q_m), electrical properties (conductivity) and crystal structure for compositions were quantified. Compositions with similar amount of Zn-doping were analyzed for reference. A drastic increase in electrical conductivity at ?0.3/?0.5 mol% Mg was associated with a concomitant increase in Q_m. Similar behavior in Zn-doped compositions provides a basis for a more comprehensive mechanistic understanding of acceptor doping in these lead-free piezoceramics. The very high and almost vibration-velocity-independent Q_m above 800 makes Mg-doped 0.94Na_1/2Bi_1/2TiO₃-0.06BaTiO₃ an excellent candidate for high-power application.