Pioneering dielectric materials of Sn-doped Nb0.025Ti0.975O2 ceramics with excellent temperature and humidity stability for advanced ceramic capacitors

Abstract

In this study, the rutile TiO₂ system, widely acclaimed for its superior properties, was enhanced through co-doping with isovalent Sn⁴⁺ ions and 2.5% Nb⁵⁺ donor ions, diverging from traditional acceptor doping practices. This novel doping strategy was implemented by employing a conventional solid-state reaction method, resulting in the synthesis of Sn-doped Nb_0.025Ti_0.975O₂ (Sn-NTO) ceramics. These ceramics demonstrated remarkable dielectric characteristics, with a high dielectric constant (ε') ranging from ∼27 000 to 34 000 and an exceptionally low loss tangent between 0.005 and 0.056 at ∼25 °C and 1 kHz. Notably, the temperature coefficient of ε', , aligned with the stringent specifications for X7/8/9R capacitors. Furthermore, the Sn-NTO ceramics exhibited a stable C_p response across various frequencies within a humidity range of 50 to 95% RH, with ΔC_p (%) values within ±0.3%, and no hysteresis loop was detected, suggesting the absence of water molecule adsorption and desorption during humidity assessments. This behavior is primarily attributed to the effective suppression of oxygen vacancy formation by the Sn⁴⁺ ions, which also affects the grain growth diffusion process in the Sn-NTO ceramics. The observed heterogeneous electrical responses between semiconducting grains and insulating grain boundaries in these polycrystalline ceramics are attributed to the internal barrier layer capacitor effect.