Abstract
The excellent electro-mechanical properties of perovskite oxide ferroelectrics make these materials major piezoelectrics. Oxygen vacancies are believed to easily form, migrate, and strongly affect ferroelectric behavior and, consequently, the piezoelectric performance of these materials and devices based thereon. Mobile oxygen vacancies were proposed to explain high-temperature chemical reactions half a century ago. Today the chemistry-enabled concept of mobile oxygen vacancies has been extrapolated to arbitrary physical conditions and numerous effects and is widely accepted. Here, this popular concept is questioned. The concept is shown to conflict with our modern physical understanding of ferroelectrics. Basic electronic processes known from mature semiconductor physics are demonstrated to explain the key observations that are groundlessly ascribed to mobile oxygen vacancies. The concept of mobile oxygen vacancies is concluded to be misleading.
Highlights
The superb electro-mechanical performance of perovskite oxide ferroelectrics makes these materials the main piezoelectrics
The vacancies (Figure 4d) do not lead to a new Considering oxygen vacancies and other defects are immobile the charge transport is specific electronic that band structure, which principally differs from thatand of that a regular stoichiometric realized(Figure by a combination of hopping of of small polarons and bandwith conductivity e for the electrons sample
An electronic effect oxygen vacancies is that increasing(σconcentration of in the and σ for the holes in the valence band (VB)), the total conductivity σ is vacancy-related hshallow occupied in-gap states, the Fermi level (EF) uplifts (Figure 4d)
Summary
The superb electro-mechanical performance of perovskite oxide ferroelectrics makes these materials the main piezoelectrics. Oxygen vacancies are accepted as the most common mobile point defects, which dramatically influence the ferroelectric behavior and, the functioning of perovskite oxide piezoelectric materials and devices made of them [1,2,3,4,5,6,7,8,9,10,11,12,13] (see Note). This attitude is widely accepted in materials chemistry and technology. The concept of mobile oxygen vacancies is inferred as misleading
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