Long-period structural modulation on the global length scale as the characteristic feature of the morphotropic phase boundaries in the Na0.5Bi0.5TiO3 based lead-free piezoelectrics. (1st February 2019)

• Record Type: Journal Article
• Authors: Adhikary, Gobinda Das; Khatua, Dipak Kumar; Senyshyn, Anatoliy; Ranjan, Rajeev
• Is Part Of: Acta materialia. Volume 164(2019)
• Page Start: 749
• Page End: 760
• Publication Date: 2019-02-01
• Subjects: Lead-free piezoceramics -- Crystal structure -- Neutron diffraction; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2018.11.016
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The inherent structural disorder has a profound effect on the dielectric, ferroelectric and the electromechanical response of the Na0.5 Bi0.5 TiO3 (NBT) based lead-free piezoelectrics. While analogous to the lead-based classical morphotropic phase boundary (MPB) systems the existence of MPB has been recognized in some derivatives of NBT displaying enhanced electromechanical response, there is a lack of clarity on the structural state of the MPB compositions on NBT-based systems on the global length scale. We have examined this issue on the well known MPB system (1-x)Na0.5 Bi0.5 TiO3 -(x)K0.5 Bi0.5 TiO3 (NBT-KBT) by carrying out structural investigations on local and global length scales using Eu +3 photoluminiscence and high-resolution neutron powder diffraction techniques, respectively. Our study reveals that the MPB of this system is characterized by the onset of a long-period modulated structure with a periodicity of ∼40 Å on the global scale. Temperature depedent neutron diffraction study revealed that the intermediate temperature P4bm phase which appears in NBT is suppressed for the MPB composition. The MPB composition rather develops a long-period modulated phase on cooling from the cubic phase. The ergodic-nonergodic relaxor ferroelectric transition occurs within this long-period modulated phase. In the non-ergodic regime, however, strong electric field irreversibly transforms the long-period modulated phase to the rhombohedral ferroelectric ( R 3 c ). We demonstrate that thermal depolarization of this system is a distinct structural event characterized by the system losing its field-induced long range rhombohedral ( R 3 c ) coherence and transforming back to the long-period modulated phase. Our study suggests that the long-period modulated phase is the primary structural feature of the MPB compositions in NBT-based piezoelectrics. Graphical abstract: Image 1