Study on the enhancement of the energy harvesting performance by the P1m1 monoclinic phase and degradation by the presence of the C1m1 monoclinic and tetragonal phases in Pb(Mg,Ti,Nb)O3 ceramics

Energy harvesting applications demand high-performance piezoelectric materials that combine excellent actuating, sensing, and transducing properties. This imposes a challenge for designing and fabricating capable and efficient piezoelectrics for energy harvesters. Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT)-based materials are well known for their high piezoelectric charge coefficient and superior electromechanical coupling performance; hence, they are competitive candidates for energy harvesting. However, in practice, the large energy harvesting figure of merit (FOM) obtained from PMN-PT-based materials is not necessarily replicable. This information is lacking in the literature. This study investigates a large quantity of PMN-PT ceramics by intentionally creating both A and B-site cation off-stoichiometry in order to show the influence of minor changes in the phases on energy harvesting properties. An electron probe microanalyzer is used to accurately quantify the compositions of the formed perovskite phases. The study finds that the Mg content in the resulting perovskite phases is consistently deficient by ∼15% compared to the commonly proposed theoretical stoichiometry. It is also found that the Mg-deficient compound promotes the formation of a specific monoclinic phase (Pm), which is beneficial for improving the FOM by up to 170%. The optimum FOM achieved in this study is 1.9 times as high as the values reported in the literature. On the other hand, the formation of another monoclinic phase (Cm) or the coexistence of a secondary tetragonal phase degrades the properties despite being at the morphotropic phase boundary. The compositional window for forming the favorable Pm phase proves to be narrow.