Investigation the effects of sintering aid cuo addition on the properties of non-stoichiometric [Na0,5Bi0,5TiO3]0,75-[Sr1-xTiO3-x]0,25 ceramics

Electroceramic materials represent a specialized class of materials with various applications, including sensors, circuit substrates, actuators, energy harvesting, energy storage, converters, and electric motors. Within this material class, piezoelectric/ferroelectric ceramics exhibiting superior electrical and electromechanical properties pose a potential threat to the environment and human health due to the lead content they contain. Consequently, the use of lead-containing ceramic compositions is restricted by various legal regulations. Intensive research and development efforts are underway to explore lead-free electroceramics as alternatives, with Lead-Free Sodium Bismuth Titanate (Na0.5Bi0.5TiO3-NBT) electroceramics emerging as potential materials due to their unique properties. In this thesis study, the NBT-based ceramic composition was modified with strontium, resulting in the synthesis of [Na0.5Bi0.5TiO3]0.75-[Sr1-xTiO3-x]0.25 (x=0.25) through the solid-state calcination method. Following the synthesis stage, copper oxide (CuO) was added to the powders in different mole ratios (0-1.5) to aid in densification during sintering of the stock powders. After the addition of binders, the powders were granulated and shaped into disk forms using a uniaxial press. The ceramics were then sintered for 4 hours at temperatures of 1175 °C, 1200 °C, 1225 °C, and 1250 °C, and their phase formation, microstructure, density, and electrical properties were examined. Post-calcination X-ray diffraction (XRD) analyses confirmed the formation of a pure perovskite phase. Secondary phase presence at 2θ angles of 27°-28° and 34°-35° was detected depending on the increasing CuO content and sintering temperature. Pore distribution was homogeneous, and intragranular fracture behavior was observed. The highest density ratio, reaching 99% of the theoretical density, was achieved in ceramics with 0.5% CuO content sintered at 1200 °C. Temperature-dependent dielectric constant measurements revealed a peak behavior indicates phase transformation starting at 141 °C. The dielectric loss (tand) was lower than 0.15. At room temperature, the dielectric constant (K) was calculated to be 1628 at a frequency of 1 kHz. The Curie temperature was measured in the range of 293 °C to 305 °C depending on the doping ratio. Electric field-induced polarization graphs at room temperature indicated standard ferroelectric behavior. It was observed that as the CuO content increased, hysteresis losses increased due to the development of A.C. conductivity.