Origin of Ferroelectricity and Multiferroicity in Binary Oxide Thin Films

Abstract

The observation of ferroelectric, ferromagnetic and ferroelastic phases in thin films of binary oxides attract the broad interest of scientists and engineers. However, the theoretical consideration of observed behaviour physical nature was performed mainly for HfO2 thin films from the first principles, and in the framework of Landau-Ginzburg-Devonshire (LGD) phenomenological approach with a special attention to the role of oxygen vacancies in both cases. Allowing for generality of the LGD theory we applied it to the group of binary oxides in this work. The calculations have been performed in the assumption that oxygen vacancies, as elastic dipoles, can be partially transformed into electric dipoles due to the defect site-induced and/or surface-induced inversion symmetry breaking (via e.g. piezoelectric effect), and can "migrate" entire the depth of an ultra-thin film. We calculated the dependence of the film polarization on the applied voltage for room temperature and different film thickness. Since the many films of binary oxide are ferroelectric and ferromagnetic due to the same oxygen vacancies, they can be multiferroics. Performed calculations have shown that thin films of binary oxides can be considered as a new wide class of multiferroics with broad spectra of physical properties useful for application in nanoelectronics and nanotechnology. The properties can be controlled by the choice of oxygen vacancies concentration, film thickness and special technological treatment, such as annealing.

A phase field model combined with a genetic algorithm for polycrystalline hafnium zirconium oxide ferroelectrics

“…The values of the elastic constants and electrostriction coefficients used for the phase field simulations are C 11 = 400.92 GPa, C 12 = 127.10 GPa, C 13 = 133.00 GPa, C 22 = 397.30 GPa, C 23 = 99.30 GPa, C 33 = 353.30 GPa, C 44 = 91.66 GPa, C 55 = 84.17 GPa, C 66 = 127.67 GPa, Q 13 = −0.02 m 4 C −2 , Q 23 = −0.015 m 4 C −2 , and Q 33 = −0.030 m 4 C −2 . Note that, in this work, due to the lack of proper experimental/first-principles based statistics, we assume the electrostrictive coefficients in a similar manner described by Glinchuk et al 63…”

Ferroelectric Devices for Intelligent Computing

“…Doped-HfO 2 materials have three types of crystal structures, namely, monoclinic, tetragonal, and cubic structures. The phase transition can be achieved through several approaches, for example, application of mechanical stress, postdeposition annealing, and application of higher deposition pressure [26,27]. In 2011, Böscke et al discovered that the use of Si as a dopant could facilitate the formation of asymmetric orthorhombic-phased HfO 2 and hence the generation of ferroelectricity in the film [20].…”

Oxygen-vacancy induced ferroelectricity in nitrogen-doped nickel oxide

“…The fact that we have seen ferroelectricity only in the oxygen-deficient N-doped samples (as was shown by XPS measurements) comes as no surprise. Indeed, numerical calculations have shown that ferroelectricity in binary oxide thin films, and generally multiferroicity, is related to oxygen vacancies [43]. In this case, oxygen vacancies, as elastic dipoles, can be partially transformed into electric dipoles due to symmetry-breaking interfaces and defects (including grain boundaries in the case of polycrystalline samples), around which vacancies tend to accumulate by diffusing through the sample.…”