Evolution of local heterogeneity towards flat free energy landscape: Optimization of piezoelectric response in PNN-PZ-PT at morphotropic phase boundary

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A precisely specified compositional landscape of two distinct ferroelectric systems – morphotropic phase boundary (MPB) – possesses ultrahigh piezoelectricity, where generically a flat energy profile is favoured under thermodynamic consideration. A more exotic and technologically appealing phase is unlocked when ternary-based morphotropic phase boundary compositions are formulated via revisiting the thermal and compositional stability. Local structure heterogeneity is another generic route towards optimization of the piezoelectric performance via rare earth doping, as rare-earth doping introduces the local structural distortions. To enhance piezoelectric response, we adopt rare earth Sm 3+ doping into ternary based morphotropic phase boundary 0.55Pb(Ni 1/3 Nb 2/3 )O 3 –0.135PbZrO 3 –0.315PbTiO 3 samples. The effect of Sm 3+ doping on the structure, microstructure, dielectric, ferroelectric and piezoelectric properties of 0.55Pb(Ni 1/3 Nb 2/3 )O 3 –0.135PbZrO 3 –0.315PbTiO 3 were investigated. Dielectric spectroscopy and order parameter analysis collectively reveal that the free energy landscape of morphotropic phase boundary is further softened via local structural heterogeneity, enabled via rare earth doping. As a result of free energy flattening, dielectric and piezoelectric responses of Sm 3+ doped system are significantly enhanced. Piezoelectric coefficient increases from 545pC/N ( x = 0%) to 810pC/N ( x = 1%) with Sm 3+ doping. Observed results suggest that the piezoelectric and ferroic performances of morphotropic phase boundary based 0.55Pb(Ni 1/3 Nb 2/3 )O 3 –0.135PbZrO 3 –0.315PbTiO 3 can further be improved by hetero-structural tuning via optimized rare earth doping.