(1 of 10) 1500181 wileyonlinelibrary.com IntroductionFerroelectric thin fi lms have broad application in society ranging from nonvolatile memories to microrobotics and integrated capacitors. As the sizes of devices and the thicknesses of fi lms decrease, the specifi c surface and interfacial areas increase signifi cantly. At these progressively smaller length scales, interfacial phenomena such as interdiffusion and interface reactions are promoted and can have benefi cial or deleterious consequences on the resultant fi lm and device properties and functionality. [1][2][3][4] Thus, an understanding of interfacial phenomena between dissimilar materials is of paramount importance in materials and devices of small length scale.Solution-based chemical routes have become effective for the synthesis of ferroelectric lead zirconate titanate (PZT) thin fi lms on diverse substrates. [5][6][7][8] In these routes, a solution is spin cast on a substrate and then subsequently heated to induce crystallization of the ferroelectric fi lm. For Pb-based ferroelectric fi lms Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor-dielectric and thermoelectric-semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution-derived lead zirconate titanate (PZT) ferroelectric thin fi lms, the evolution of buried interfaces during synthesis (including dielectricmetal and metal-metal) is thought to dramatically infl uence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT fi lms on platinized Si wafers-including in situ X-ray diffraction during thermal treatment, aberration-corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)-oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt 3 Pb and Pt 3 Ti phases.
Strain and applied external electric fields are known to influence domain evolution and associated ferroelectric responses in ferroelectric thin films. Here, phase‐field simulations are used to predict equilibrium domain structures and polarization‐field (P‐E) hysteresis loops of lead zirconate titanate (PZT) thin films under a series of mismatch strains, ranging from strongly tensile to strongly compressive. In particular, the evolution of domains and the P‐E curves under different applied strains reveal the mesoscale mechanism, the appearance of in‐plane polarization during domain switching, that is responsible for a relatively small coercive field and remnant polarization. A Landau energy distribution is analyzed to better understand the domain evolution under various strain conditions. The results provide guidance for choice of mismatched strains to yield the desired P‐E hysteresis loops and the domain structures.
The formation of intermetallic secondary phases, such as Pt3Pb, has been observed experimentally at PbTiO3/Pt and Pb(Zr,Ti)O3/Pt, or PZT/Pt, interfaces. Density functional theory calculations are used here to calculate the work of adhesion of these interfacial systems with and without the secondary intermetallic phase. The charge density maps of the interfaces reveal the electronic interactions at the interface and the impact of the secondary phase. In addition, Bader charge analysis provides a quantitative assessment of electron transfer from the perovskites to the Pt. Analysis of the band diagrams indicates an increase of the potential barrier associated with electron transfer due to the formation of the Pt3Pb at PZT/Pt interfaces.
Interfaces between functional ceramics, such as Pb(Zr0.5Ti0.5)O3 or PZT, and metal electrodes, such as Pt, are important for many devices. Maintaining an interface that is free of secondary phases is necessary for the efficient transfer of electrons and device function. However, there are instances where unstable transient phases form at the interface due to atomic diffusion, such as Pt3Pb. Here, we investigate the migration barriers for the diffusion of Pb across the PZT/Pt and PZT/Pt3Pb interfaces using density functional theory (DFT) and the climbing image nudge elastic band (c‐NEB) method. Our calculation models take into account the influence of atmospheric conditions on Pb diffusion through the preferential stabilization of defects near the interface as a result of changes to the Pb and O chemical potentials. In addition, the PZT structures that are stable above and below the Curie temperature are considered. The migration barriers are predicted to be strongly dependent on atmospheric conditions and the phase of the PZT, tetragonal or cubic. In particular, an inversion of the Pb diffusion direction at the PZT/Pt interface is predicted to take place as the oxygen partial pressure increases. This prediction is confirmed by experimental in situ X‐ray diffraction measurements of a PZT/Pt interface.
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