Ultrafast collective oxygen-vacancy flow in Ca-doped BiFeO3

Abstract

The ultrafast motion of oxygen vacancies in solids is crucial for various future applications, such as oxide electrolytes. Visualization and quantification can offer unforeseen opportunities to probe the collective dynamics of defects in crystalline solids, but little research has been conducted on oxygen vacancy electromigration using these approaches. Here, we visualize electric-field-induced creation and propagation of oxygen-vacancy-rich and-poor competing phases and their interface with optical contrast in Ca-substituted BiFeO 3 that contains a high density of mobile oxygen vacancies. We quantitatively determined the drift velocity of collective migration to be on the order of 100 μm s −1 with an activation barrier of 0.79 eV, indicating a significantly large ionic mobility of 2 × 10 −6 cm 2 s −1 V −1 at a remarkably low temperature of 390°C. In addition, visualization enables direct observation of fluidic behavior, such as the enhancement of conduction at channel edges, which results in U-shaped viscous propagation of the phase boundary and turbulence under a reverse electric field. All of these results provide new insights into the collective motion of defects.

Manipulation of Oxygen Vacancy for High Photovoltaic Output in Bismuth Ferrite Films

“…Moreover, the photocurrent density (short-circuit current density, J SC ) of BFO observed in bulk crystals or thin films is very small, usually several μA/cm 2 below the magnitude of mA/cm 2 for general silicon-based solar cells. ,, It makes the power conversion efficiency of BFO-based photovoltaic devices very poor, usually less than 1%, severely hampering future applications in ferroelectric photovoltaics or photoelectronics. , Thanks to the fruitful investigations on the physical properties of BFO compounds in the past, oxygen vacancy is believed to play a key role on leakage and ferroelectric properties of BFO, which in turn should have great impacts on its photovoltaic properties. ,, …”

“…14,33 Thanks to the fruitful investigations on the physical properties of BFO compounds in the past, oxygen vacancy is believed to play a key role on leakage and ferroelectric properties of BFO, which in turn should have great impacts on its photovoltaic properties. 23,34,35 On the basis of the above analysis and discussion, we proposed a novel design to realize high photovoltaic output in bismuth ferrite films. In this framework, manipulation of oxygen vacancy by adjusting the content of Bi in the BFO film capacitor finally achieved more than 1000 times improvement on its photovoltaic output (V OC × J SC ).…”

Control of electrical resistance and magnetoresistance by electric-field-driven oxygen ion migration in a single GdOx wire

“…This large decrease in resistivity indicates that a reduction process, from insulator-like GdO x to metal-like Gd, occurs when the oxygen ions are driven by an electric field. To provide more direct evidence, we measured the real-time color change of TaO x /GdO x using an optical microscope because the change in oxygen ion concentration is reflected by changes in the optical contrast 20 . We first applied a negative electric field for 1000 s to push the oxygen ions to the right edge of the wire and then reversed the electric field polarity.…”

High oxide-ion conductivity in acceptor-doped Bi-based perovskites at modest doping levels

“…21 Its electrical properties that include mixed ionic-electronic and oxide ion conductivity in acceptor-doped BF, depend strongly on processing conditions. [22][23][24][25][26][27] High levels of oxygen permeability were reported in Sr-doped BF 23 and Impedance Spectroscopy (IS) measurements showed the level of oxide ion conductivity in Ca-doped BF (with 3, 5 and 30 at% replacement of Ca for Bi on the A-site) is as high as that observed in the well-known fluorite-based solid electrolyte, yttrium-stabilised zirconia, 8YSZ. 24 Ionic conduction was explained on the basis of A-site Ca-doping compensated by oxygen vacancy creation V O À Á as follows (using Kröger-Vink notation):…”