electroluminescent devices, [ 2 ] electrochromic windows, [ 3 ] and transparent amorphous conductors [ 4 ] remains poorly understood. Abrupt changes of resistance in response to electrical stress are hallmarks of correlated electron and ion dynamics and an obvious manifestation of structural dynamics; such phenomena have been reported in a variety of oxides with a range of stoichiometries in different applications. Materials studied include indium tin oxide, zinc, vanadium, nickel, and titanium oxides, and silicon oxide, all of which have a variable degree of substoichiometry that affects the dynamics of resistance change. Here, we employ a suite of structural characterization techniques, including bias-induced resistance changes, to probe dynamic structural changes in amorphous oxides. Abrupt resistance changes are not necessarily central to device functionality, and in some cases, such as electroluminescence, are detrimental. Nevertheless, they demonstrate an extreme response to electrical stress. Silicon oxide, which we study here, is a technologically important oxide representative of the broader class of metastable amorphous oxides. It is historically one of the most studied materials, and the remarkable dynamics that we uncover are thus all the more surprising.Existing models for defect generation and electrical breakdown in oxides are often restricted to crystalline and stoichiometric materials; amorphous oxides present a formidable modeling challenge. Nevertheless, recent work on resistance switching highlights local structural and chemical changes driven by sub-breakdown electrical stress. Research into resistance changes in silicon oxide dates back to the 1960s and 1970s, when irreversible electrical breakdown was widely studied. [5][6][7][8] More recently, there have been reports of intrinsic reversible (soft) breakdown of silicon oxide, [9][10][11] usually ascribed to the formation of chains of oxygen vacancies [ 12 ] produced by fi elddriven movement of oxygen ions. The reversibility of these changes is of the greatest interest, as it probes the dynamics of oxides under controlled stress and provides a model for the initial stages of irreversible dielectric breakdown. In terms of applications, nonvolatile resistive random access memory (RRAM) [ 1 ] or analogue neuromorphic devices [ 13,14 ] are important technological areas that exploit reversible dynamic changes in oxide local structure. However, they are by no means the only applications relying on electrically stressed amorphous oxides. [2][3][4] The observation of quantized conductance in electrically stressed silicon oxide suggests further applications in quantum technology [ 15 ] while, in other fi elds, studies of electroluminescence from silicon-rich silicon oxide demonstrate that its optical properties depend critically on the sequence of applied voltage stress; over-stressing produces permanent Functional oxides are fundamental to modern microelectronics as high quality insulators, transparent conductors, electroluminescent and electrochro...

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Using density functional theory (DFT) calculations, we investigated oxygen vacancy diffusion and aggregation in relation to dielectric breakdown in amorphous silicon dioxide (a-SiO). Our calculations indicate the existence of favourable sites for the formation of vacancy dimers and trimers in the amorphous network with maximum binding energies of approximately 0.13 eV and 0.18 eV, respectively. However, an average energy barrier height for neutral vacancy diffusion is found to be about 4.6 eV, rendering this process unfeasible. At Fermi level positions above 6.4 eV with respect to the top of the valence band, oxygen vacancies can trap up to two extra electrons. Average barriers for the diffusion of negative and double negatively charged vacancies are found to be 2.7 eV and 2.0 eV, respectively. These barriers are higher than or comparable to thermal ionization energies of extra electrons from oxygen vacancies into the conduction band of a-SiO. In addition, we discuss the competing pathways for electron trapping in oxygen deficient a-SiO caused by the existence of intrinsic electron traps and oxygen vacancies. These results provide new insights into the role of oxygen vacancies in degradation and dielectric breakdown in amorphous silicon oxides.

The layered oxide LiNiO2 (LNO) has been extensively investigated as a cathode active material for lithium‐ion batteries. Despite LNO's high gravimetric capacity, instability issues hinder its commercialization. It suffers from capacity loss during electrochemical cycling and is difficult to synthesize without defects. This is related to poor structural stability, leading to decomposition into the parent rock‐salt‐type oxide. In order to understand such phase transformations and to develop measures to inhibit them, the development of techniques able to image all atoms is crucial. In this study, the use of a fast, pixelated detector and 4D imaging in scanning transmission electron microscopy are explored to tackle this challenge. Selecting specific angular regions in the diffraction patterns and calculating virtual annular bright‐field images significantly enhances the contrast of the lithium atoms, such that all atoms are visible even in realistic samples. The developed technique is applied to image the layered‐to‐rock salt phase transition region. The data show that in this region, nickel atoms are in tetrahedral positions and the oxygen atoms are asymmetrically distributed. Taken together, the results shed light on the phase transformation mechanism at the atomic scale and can guide future research toward stabilizing LNO.