Ferroelectric and Incipient Ferroelectric Properties of a Novel Sr_(9-x)Pb_xCe2Ti2O_(36)(x = 0-9) Ceramic System

摘要

Sr_(9-x)Pb_xCe2Ti_(12)O_(36) system is derived from the perovskite SrTiO3 and its chemical formula can be written as (Sr_(1-y)Pb_y)_(0.75)Ce_(0.167)TiO3. We investigated dielectric response of Sr_(9-x)Pb_xCe2Ti_(12)O_(36) ceramics (x = 0—9) between 100 Hz and 100 THz at temperatures from 10 to 700 K using low- and high-frequency dielectric, microwave (MW), THz, and infrared spectroscopy. We revealed that Sr9Ce2Ti_(12)O_(36) is an incipient ferroelectric with the R3c trigonal structure whose relative permittivity ε' increases from 167 at 300 K and saturates near 240 below 30 K. The subsequent substitution of Sr by Pb enhances ε' to several thousands and induces a ferroelectric phase transition to monoclinic Cc phase for x ≥ 3. Its critical temperature T_c linearly depends on the Pb concentration and reaches 550 K for x = 9. The phase transition is of displacive type. The permittivity ε' follows the Barrett formula (typical for quantum paraelectrics) in samples with x ≤ 2. The MW dispersion is lacking and quality factor Q is high in samples with low Pb concentration, although the permittivity is very high in some cases. However, because of the lattice softening, the temperature change of the permittivity is rather high. The best MW quality factor was observed for x = 1: Qf = 5800 GHz and ε' = 250. Concluding, the dielectric properties of Sr_(9-x)Pb_xCe2Ti_(12)O_(36) are similar to those of Ba_(1-x)Sr_xTiO3 so that this system can be presumably used as an alternative for MW devices or capacitors.