Re-entrant relaxor behavior of Ba5RTi3Nb7O30 (R = La, Nd, Sm) tungsten bronze ceramics

Ba5RTi3Nb7O30 (R = La, Nd, Sm) tungsten bronze ceramics were prepared, and the dielectric and ferroelectric properties were investigated over a broad temperature range. The relaxor nature was determined for all compositions in their permittivity curves, and a second anomaly of the dielectric loss (tan δ) was observed around 250 K in Ba5NdTi3Nb7O30 and around 275 K in Ba5SmTi3Nb7O30. Both the maximum and remanent polarization tended to decrease and vanish at low temperatures in the ferroelectric phase for all compositions, which was referred to as the low temperature re-entrant relaxor behavior. The remanent polarization increased with decreasing temperature first and then reached the maximum value at the re-entrant temperature (Tr). For Ba5RTi3Nb7O30 (R = La, Nd, Sm), Tr decreased with the radius of R3+ cations and the applied field amplitude.