Reversible evolution of ferroelectric-antiferroelectric phase transition in lanthanum-modified NaNbO3-based ceramics

Sodium niobate (NN) lead-free perovskites have been concentrated on due to high performance and abundant phase structure. The complex structure evolution has become a hot topic of research for this kind of materials. In this work, antiferroelectric phase is recovered by introducing La3+ dopant from modified ferroelectric states, indicating reversible composition-induced antiferroelectric-ferroelectric (AFE-FE) phase transition in NN-based ceramics. Significantly, change tendency of decreasing first and then increasing appears for phase transition temperature with increasing La3+, which is different from general phenomenon for ions dopant. Antiferroelectric orthorhombic (Pbma) is induced from ferroelectric tetragonal (P4mm) with a transient state of paraelectric cubic (Pm3m) via enhancing La3+. Further, substitution on A-site and A/B-sites are revealed with low and high content of La3+, respectively, accompanied by decreased first and then increased oxygen vacancy. Moreover, obviously deteriorated piezoelectric response is observed along with poor domain switching due to the vanishing ferroelectric domain for FE-PE-AFE phase transition. Meanwhile, weak strain, piezoelectric and dielectric properties are observed for antiferroelectric phase with antiparallel dipoles, while enhanced strain and dielectric permittivity are gained around ferroelectric-paraelectric coexistence or paraelectric region originating from electric field-induced ferroelectric state from polar nanoregions. Thus, this work demonstrated an abnormal phase transition in NN-based ceramics, promoting the understanding of antiferroelectrics.