Temperature-Stable Linear Dielectric Response of Low-Temperature Sintered La-Doped Bi₂SiO₅ Ceramics

Doping of a small amount of La 3+ into ferroelectric Bi 2 SiO 5 induces the disorder of SiO 4 chains in its crystal structure, leading to a transition into a paraelectric phase with a superior temperature stability of the dielectric permittivity. In this study, we attempted to fabricate bulk La-doped Bi 2 SiO 5 ceramics through sintering with the aim of applying Bi 2 SiO 5 to ceramic capacitors. (Bi 1– x La x ) 2 SiO 5 fine powders with a La content x of up to 0.05 were synthesized by a sol–gel method and then sintered at low temperatures below 740 °C. The undoped Bi 2 SiO 5 decomposed into secondary phases after sintering at temperatures over 640 °C due to its metastable nature, whereas La doping retarded the thermal decomposition, enabling sintering at higher temperatures. As a result, high relative densities near 90% were achieved for (Bi 1– x La x ) 2 SiO 5 ceramics with x = 0.03 and 0.05 without the formation of secondary phases. The dielectric peak due to the ferroelectric–paraelectric phase transition at around 400 °C disappeared with the increase in La content. The obtained (Bi 0.97 La 0.03 ) 2 SiO 5 ceramic consequently exhibited a temperature-stable dielectric permittivity over a wide temperature range between −160 and 500 °C. A highly linear large-field dielectric response of the (Bi 0.97 La 0.03 ) 2 SiO 5 ceramic was observed under varying electric fields up to 220 kV cm –1 (at 20 °C) and at varying temperatures between −60 and 60 °C (at 100 kV cm –1 ).