Structural Instability in Electrically Stressed, Oxygen Deficient BaTiO₃ Nanocrystals

Abstract

The dynamics of oxygen vacancies under external stimuli dominates the performance of many solid-state devices, including capacitors, oxide memristors, anionic conductors, etc. By means of in situ transmission electron microscopy, it is found in BaTiO 3 perovskite nanocrystals that formation of oxygen vacancies due to electrical stressing renders the oxide amorphizable under electron beam illumination, suggesting the presence of a threshold concentration of oxygen vacancy affecting the structural stability of BaTiO 3 crystals upon high energy radiation. In contrast to the structural change, the resistivity of the nanocrystal seems not liable to the amorphization prior to dielectric breakdown at higher voltage bias. It is proposed that an increase in oxygen vacancy content promotes oxygen mobility in the perovskite structure allowing electron beam induced electric field to modify the local structure and composition. The in situ observations reveal the central role of oxygen vacancies in the structural stability of perovskites which is of paramount importance to their applications in extreme environments and suggest a potential new route to micro-processing perovskite oxides using the electron beam via oxygen vacancy management without severely compromising the electric property.

Atomic-scale fatigue mechanism of ferroelectric tunnel junctions

“…To lower the increased energy, the lattices have to be distorted, which may result in the destruction of perovskite structure. There are two possible ways for the lattice collapse of the oxygen-deficient BTO under pulse cycling: (i) decomposition to the parent oxides, such as BaO, TiO 2-δ , and Ti 2 O 3 , as suggested by the calculations, and (ii) transformation to amorphous BTO because oxygen vacancy–induced amorphization has been experimentally observed in BTO nanocrystals ( 41 ) and theoretically simulated in bulk BTO by molecular dynamics ( 42 ). No matter which situation takes place, the consequence is the loss of ferroelectricity in region B.…”

Oxygen-vacancy rich IrxMo1−xOy nanofibers for oxygen evolution reaction: excellent pH-universal and electrolyte-concentration-independent catalytic activity

“…Previous studies have noted that amorphous samples tend to exhibit a higher number and concentration of oxygen vacancies compared to their crystalline counterparts. 44,45 This can be attributed to the lack of long-range order and increased atomic disorder in amorphous materials. The absence of a well-dened crystal lattice in amorphous materials provides greater exibility in accommodating oxygen vacancies.…”

In situ TEM measurement of electrical properties of individual BaTiO3 nanocubes

“…15 Benefitting from the recent success on the synthesis of doped BaTiO 3 nanocubes, 22 we report on the characterization of individual pristine and doped BaTiO 3 nanocubes by using the PI95 in situ TEM holder (single-tilt) in order to understand how doping affects the electrical properties of BaTiO 3 nanocubes. Pristine and Cr-or La-doped BaTiO 3 cuboidal nanoparticles were placed directly between two electrodes using a procedure we reported before, 23,24 and their electrical properties were measured in situ at electric fields up to 900 kV/cm. Cr in BaTiO 3 has been shown to replace Ti and forms Cr 3þ or Cr 4þ ions in the lattice depending on the annealing condition.…”

“…Both Si wedge and W probe were chemically etched by alkaline solutions to remove the native oxide layer before their usage, and the details of the procedure can be found in our previous reports. 23,24 Due to the nature of cantilever structure of the W probe tip, remote or minor disturbances will cause an uncontrolled shaking or movement of the probe. This uncontrolled movement becomes significant for BaTiO 3 nanocubes because of their tiny size.…”

“…10 Our previous work showed that strong electron beam radiation can introduce oxygen vacancies in BaTiO 3 nanocrystals (commercially purchased with a size of a few hundreds of nanometers), and the resistance of the nanocrystal after amorphization shows a significant decrease at $500 kV/cm. 23 The Joule heating effect of nanocubes may also contribute to the oxygen vacancy formation in BaTiO 3 nanocubes due to the low oxygen partial pressure within the TEM chamber. The continuous change in resistance with electric field has been observed in metal oxides, such as TiO 2 , whereby the mechanism is attributed to the coupled motion of electrons and ions or vacancies within the oxide layer under applied electric fields.…”