Abstract: The effects of Cr₂O₃ addition on piezoelectric properties，microstructure and morphology of the domain of PZT-PMN ceramics
were studied by TEM, SEM, ESR and other conventional electrical methods. The measurement results of piezoelectric properties showed that the
Cr₂O₃ addition was effective in increasing the K_p and Q_m when its concentration was below 0.06wt%, which indicated
that Cr-doped PZTMN ceramics possessed the properties of “soft” and “hard” piezoelectrics simultaneously. Furthermore, the properties were
found to get “hard” with the increase of sintering temperature even for the ceramics with the same compositions. Electron Spin Resonance (ESR)
analysis showed that Cr ion coexisted in both Cr³⁺ and Cr⁵⁺, and the valence change from Cr⁵⁺ or Cr⁶⁺ to Cr³⁺ happened
when the sintering temperature was increased, which was believed to be one of the reasons for its hardness of the properties. TEM images
revealed that, with the increment in Cr content, the normal stripe-like domain changed to wavy domain due to the domain pinning by the defect
complexes of acceptor impurities and oxygen vacancies.

Key words: Cr-doping, piezoelectric properties, morphology of domains