Prediction of Ferroelectric Behavior for PZT and Pb-Substituted Materials

抄録

In this study, first principles calculations based on density functional formalism were used to evaluate optimized structures, spontaneous polarizations, and effective charges for Sn(Zr_0.5,Ti_0.5)O₃ (SZT), Ge(Zr_0.5,Ti_0.5)O₃ (GZT), (Pb_0.875,Sn_0.125)(Zr_0.5,Ti_0.5)O₃ (PSZT), and (Pb_0.875,Ge_0.125)(Zr_0.5,Ti_0.5)O₃ (PGZT); the results were compared with corresponding values calculated for Pb(Zr,Ti)O₃ (PZT). The stability of the calculated crystal structures differed depending on whether all Pb atoms were replaced (100% substituted materials, SZT and GZT) or whether only 12.5% of Pb atoms were replaced (12.5% substituted materials, PSZT and PGZT): the structures of 100% substituted materials were compressed and unstable, while the 12.5% substituted materials maintained stable structures. Both the 100% and 12.5% substituted materials had values of spontaneous polarization nearly as large as that for PZT. For 100% substitutions, atomic displacements increased and effective charges decreased relative to values for PZT. For 12.5% substitutions, atomic displacements also increased, and the effective charge along the macroscopic polarization axis decreased due to changes in covalent bonding. We evaluated the piezoelectricity of the materials by calculating the barriers to change in polarization axes. For 100% substituted materials, the barriers were larger than that for PZT, while for 12.5% substituted materials, the barriers were smaller. Therefore, 100% substituted materials have weaker piezoelectric properties than PZT, but 12.5% substituted materials have stronger piezoelectric properties. We conclude that 12.5% substituted materials maintain the crystal structure of PZT and probably have better piezoelectric behavior than PZT. [DOI: 10.1380/ejssnt.2014.40]