Effect of Mn-doping on the structure and electrical properties of (Pb0.325Sr0.675)TiO3 ceramics

Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics (x?=?0, 0.001, 0.005, 0.01, and 0.05) were successfully prepared by traditional solid-state reaction method. It was found that the lattice constant calculated through Rietveld refinement initially increased and then decreased with increasing Mn content, which was attributed to the variation in valence state of Mn and Ti ions. The microstructure gradually varied from the coexistence of large grains and fine grains for x?=?0 to the uniform grain for x?=?0.05 by increasing the doping Mn ions. With increasing Mn content from x?=?0 to x?=?0.05, the Curie temperature (Tc) dramatically decreased from 25?°C to ??40?°C and dielectric maximum decreased from 27,100 to 13,200. Pb_0.325Sr_0.675Ti_1-xMn_xO₃ ceramics with x?=?0.001 showed the lowest dielectric loss of 0.006 with a relatively high dielectric peak value of ~ 21,000. The grain boundaries resistance obtained from the complex impedance decreased with the increase of Mn content. The decrease in resistance was ascribed to oxygen vacancies and electronics produced by the change of ionic valence state. X-ray photoemission spectroscopy revealed that Ti ions were Ti⁴⁺ and the valences of Mn ions were deduced to be mainly in the form of Mn²⁺ and/or Mn³⁺ for ceramics with low content of Mn, while the Ti ions were in the form of Ti³⁺ and Ti⁴⁺ and Mn ions were diverse valence states with the coexistence of Mn²⁺, Mn³⁺, and Mn⁴⁺ for ceramics with x?=?0.01 and 0.05.