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Defect engineering via doping exhibits considerable potential for improving the performance of environment-friendly lead-free piezoelectric materials. Owing to the susceptibility to lattice vibrations and the micro-local chemical environment, the readily available Mn/Fe transition metal elements (TMEs) facilitate the construction of defect structures. However, the role of TMEs in shaping the domain structures and the corresponding promotional mechanism of piezoelectricity need to be further decoded. Herein, we propose the different influence mechanisms of Mn and Fe ions on the ferroelectric domain and piezoelectric properties. Different concentrations of (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are obtained based on the synergy of Mn/Fe ions with oxygen vacancies. Diverse ferroelectric behaviors resulting from (MnNb/Ta′-VO••)• and (FeNb/Ta″-VO••)× defect dipoles are observed. Furthermore, the variation of the dielectric diffusiveness with the defect dipole concentration is investigated. Trace concentration of (MnNb/Ta′-VO••)• generates strong diffusiveness. With the characterization of the ferroelectric domain, this strong diffusiveness is attributed to the lattice-like domain structure. Thereafter, the mechanisms of Mn/Fe defect dipoles on the formation of domain structures are clarified. Macroscopically, the dielectric and piezoelectric properties are measured with Mn/Fe ion components. Trace Mn doping and the resulting lattice-like domain significantly enhance the piezoelectric coefficient, resulting in an increase of nearly 50% for K(Ta,Nb)O3 single crystals. This work highlights the tremendous potential of TME-induced defect dipoles for modifying the ferroelectric domain and provides a reference paradigm for improving piezoelectricity through defect engineering.
Huang et al. (Mon,) studied this question.