Oxide chemistry and local structure of PbZrxTi1-xO3 studied by density-functional theory supercell calculations

Abstract

The PbZr x Ti 1Ϫx O 3 ͑PZT͒ disordered solid solution is widely used in piezoelectric applications due to its excellent electromechanical properties. The disorder is caused by the random arrangement of B cations. To understand the relationship between properties of constituent atoms, local structure, and compositional phase transitions, we examine the response of the individual Pb atoms, B cations, and oxygen cages to the variation in the Zr/Ti arrangement and composition through first-principles density-functional-theory ͑DFT͒ calculations on a variety of PZT supercells. We use a statistical analysis of the relaxed DFT structures to identify crystal chemical structural motifs present in the Zr-rich rhombohedral, 50/50 monoclinic, and Ti-rich tetragonal phases of PZT and to examine the influence of composition variation on the motifs. We find that the distortions of the structure away from the ideal perovskite structure are governed by an interplay of bonding, electrostatic, and short-range repulsive interactions that depends on the B-cation arrangement. For Pb-atom displacements, there is a competition between electrostatic and bonding interactions that favor ordered collinear displacements, and local repulsive interactions that favor disorder. This competition is strongly affected by the changes in Zr/Ti composition and leads to compositional phase boundaries in PZT.

Structure and Polarization in the HighTcFerroelectricBi(Zn,Ti)O3Grinberg1, Suchomel2, Dmowski3 et al. 2007Phys. Rev. Lett.Self Cite1392881View full textAdd to dashboardCite

“…The shoulder at 2.2 Å in the experimental PDF is due to the short Bi-O distances created by the large Bi displacements. In the higher-resolution DFT PDF, another shoulder is apparent at 2.5 Å , consistent with the off-center displacement of Pb ions [16,29].…”

Enhanced ferroelectric polarization and possible morphotrophic phase boundary in PZT-based alloys

“…The computed value for PZT is in good agreement with previously calculated values 12,[16][17][18][19][20] . The value for PZT-BZrT is smaller, at 0.72 C/m 2 , and largely arises from the planar displacements depicted in the bottom left of Fig.…”

Special quasirandom structures to study the(K0.5Na0.5)NbO3random alloy

“…Collectively, this is indicative of a global response of the cations, all displacing along the direction of the bulk polarization. Such a global response of cations to the overall polarization has been previously used to understand why the three composition-dependent phases of PZT have very similar PDFs but very different macroscopic polarizations [14]. In PZT, the overall macroscopic polarization was found to be due to a competition between local distortions due to ionic repulsion, primarily between Pb and Zr, and the cooperative displacement of the cations along the overall polarization direction [14].…”

“…Such a global response of cations to the overall polarization has been previously used to understand why the three composition-dependent phases of PZT have very similar PDFs but very different macroscopic polarizations [14]. In PZT, the overall macroscopic polarization was found to be due to a competition between local distortions due to ionic repulsion, primarily between Pb and Zr, and the cooperative displacement of the cations along the overall polarization direction [14]. Previous work of Suewattana and Singh indicates that in KNN, the B-B-site response is a result of stiff force constants between the B-site cations [38].…”

“…Alternatively, interatomic potentials that can model large unit cells can account for the effects of local variations in bonding. These methods have been demonstrated to be successful at representing the physical properties of the ABO 3 perovskite compounds PZT [14] and BaTiO 3 -SrTiO 3 [15,16]. Unfortunately, these approaches require extensive effort to parametrize the potentials and necessitate large experimental or computational datasets.…”