IntroductionPyroelectric materials are widely used in the field of infrared detection. With the development of miniaturization and integration of devices, it is particularly important to develop lead-free pyroelectric sensitive elements with superior pyroelectric properties and high depolarization temperature compatible with reflow soldering process. In this paper, different mass fractions of Mn ions were doped into 0.96NaNbO₃–0.04BaTiO₃ matrix materials via a component gradient design. The effect of doping amount on the microstructure, ferroelectric properties, dielectric and pyroelectric properties of 0.96NaNbO₃–0.04BaTiO₃ ceramics was systematically investigated. The results show that when the doping amount of Mn is 0.4%, the ceramics have the optimum pyroelectric properties, which has a practical prospect of uncooled infrared detection.MethodsAll the components of sodium niobate ceramics were prepared by a solid-phase sintering method. The series of components were weighed according to the stoichiometric ratio, and the raw materials with anhydrous ethanol were ground in a stirred bead mill with zirconia beads at 400 r/min for 6 h. After being dried and shaped, the ground material was was pre-sintered at 1000 ℃ for 4 h, and then subjected to milling and drying. Green wafers with a diameter of 12 mm were prepared by pressure cold isostatic pressing at 200 MPa for 5 min after adding 10% PVA. The wafers were degummed at 600 °C for 2 h to remove organic matter and other impurities. To prevent the volatilization of sodium at a high temperature, the padding with the same composition was used for burial treatment, and the padding was kept at the corresponding temperature for 3 h and then cooled naturally. The sintered ceramic wafers were ground to fine particles with the size of 300 μm, coated with silver electrodes on both sides, and polarized in silicone oil under an electric field of 8-10 kV/mm at 80 ℃ for 15 min. The electrical properties were tested after 24 h.Results and discussionThe microstructural morphology, dielectric properties, temperature stability, and pyroelectric properties of 0.96NN–0.04BT ceramics doped with 0–0.6% Mn are investigated. The results show that doping Mn ions significantly improves the sintering characteristics of 0.96NN–0.04BT ceramics, enhances the density, and the relative densities of all components reach above 90%. The NN–BT ceramic grain size increases with the increase of the doping amount. The substitution position of Mn ions causes changes in the electrical properties of the ceramic as the Mn doping content increases gradually. The concentration of oxygen vacancies caused by Na⁺ evaporation decreases when Mn ions substitute for A-site vacancies, which is beneficial to reducing the ceramic dielectric constant and dielectric loss, thus significantly improving the detection sensitivity factor. However, as the Mn doping content further increases, the imbalance of charges is prone to attract oxygen vacancies to form defect dipoles due to the heterovalent substitution of Mn ions on the B-site, thereby producing domain wall pinning effects. Also, the defect dipoles cause the increasing coercive field of the doped material and make it difficult to fully polarize, resulting in the material that is unable to fully utilize its pyroelectric properties.ConclusionsThe ceramic could have more suitable characteristics for pyroelectric requirements via appropriately adjusting the Mn doping concentration. The ceramic with Mn ion doping mass fraction of 0.4% had the optimal pyroelectric performance (i.e., the pyroelectric coefficient of 2.11×10^–8 C·cm^–2·K^–1, and the F_v value of 3.74×10^–2 m²·C^–1), which was greater than 1.3 times and 1.8 times of the un-doped component. The coercive field reduced from 4.04 kV/mm of the un-doped component to 3.17 kV/mm, which was decreased by 21.5%. The results of the thermal stability test proved that the depolarization temperature could be maintained at 310 ℃, which had a practical prospect for non-cooled infrared detection.