Improving the dielectric temperature stability of BiSiO-based ceramics through the spontaneous formation of paraelectric-ferroelectric nanocomposite structures.

The substitution of a portion (∼3%) of Bi in ferroelectric BiSiO ceramics with La induces a paraelectric phase and stabilizes the dielectric permittivity by eliminating the ferroelectric-paraelectric phase transition. However, the non-negligible negative temperature dependence of the permittivity remains an issue for practical applications in capacitors, resonators, and antennas. Herein, we show that the additional substitution of Si with Ge in paraelectric (BiLa)SiO can substantially improve its dielectric temperature stability. Ceramic samples with compositions of (BiLa)SiGeO with up to 0.3 were prepared a sol-gel process and subsequent low-temperature sintering below 720 °C. The incorporation of Ge stabilized the ferroelectric phase with an elevated Curie temperature, leading to the spontaneous formation of a paraelectric-ferroelectric nanocomposite structure. The fraction of the ferroelectric phase increased from 0% at = 0 to 53% at = 0.3. Because of the negative and positive temperature dependence of the paraelectric and ferroelectric phases, respectively, the sample with = 0.2 exhibited a dielectric permittivity over 50 with a small temperature coefficient of -70 ± 50 ppm °C in a temperature range from -55 to 125 °C. The ceramics also showed a paraelectric-like linear polarization response under electric fields up to 280 kV cm.