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Efficient and affordable synthesis of Li⁺functional ceramics is crucial for the scalable production of solid electrolytes for batteries. Li‐garnet Li₇La₃Zr₂O_12−d(LLZO), especially its cubic phase (cLLZO), attracts attention due to its high Li⁺conductivity and wide electrochemical stability window. However, high sintering temperatures raise concerns about the cathode interface stability, production costs, and energy consumption for scalable manufacture. We show an alternative “sinter‐free” route to stabilize cLLZO as films at half of its sinter temperature. Specifically, we establish a time‐temperature‐transformation (TTT) diagram which captures the amorphous‐to‐crystalline LLZO transformation based on crystallization enthalpy analysis and confirm stabilization of thin‐film cLLZO at record low temperatures of 500 °C. Our findings pave the way for low‐temperature processing via TTT diagrams, which can be used for battery cell design targeting reduced carbon footprints in manufacturing.

 

Efficient and affordable synthesis of Li⁺functional ceramics is crucial for the scalable production of solid electrolytes for batteries. Li‐garnet Li₇La₃Zr₂O_12−d(LLZO), especially its cubic phase (cLLZO), attracts attention due to its high Li⁺conductivity and wide electrochemical stability window. However, high sintering temperatures raise concerns about the cathode interface stability, production costs, and energy consumption for scalable manufacture. We show an alternative “sinter‐free” route to stabilize cLLZO as films at half of its sinter temperature. Specifically, we establish a time‐temperature‐transformation (TTT) diagram which captures the amorphous‐to‐crystalline LLZO transformation based on crystallization enthalpy analysis and confirm stabilization of thin‐film cLLZO at record low temperatures of 500 °C. Our findings pave the way for low‐temperature processing via TTT diagrams, which can be used for battery cell design targeting reduced carbon footprints in manufacturing.

 

Ceria and its solid solutions play a vital role in several industrial processes and devices. These include solar energy-to-fuel conversion, solid oxide fuel and electrolyzer cells, memristors, chemical looping combustion, automotive 3-way catalysts, catalytic surface coatings, supercapacitors and recently, electrostrictive devices. An attractive feature of ceria is the possibility of tuning defect-chemistry to increase the effectiveness of the materials in application areas. Years of study have revealed many features of the long-range, macroscopic characteristics of ceria and its derivatives. In this review we focus on an area of ceria defect chemistry which has received comparatively little attention – defect-induced local distortions and short-range associates. These features are non-periodic in nature and hence not readily detected by conventional X-ray powder diffraction. We compile the relevant literature data obtained by thermodynamic analysis, Raman spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Each of these techniques provides insight into material behavior without reliance on long-range periodic symmetry. From thermodynamic analyses, association of defects is inferred. From XAFS, an element-specific probe, local structure around selected atomic species is obtained, whereas from Raman spectroscopy, local symmetry breaking and vibrational changes in bonding patterns is detected. We note that, for undoped ceria and its solid solutions, the relationship between short range order and cation–oxygen-vacancy coordination remains a subject of active debate. Beyond collating the sometimes contradictory data in the literature, we strengthen this review by reporting new spectroscopy results and analysis. We contribute to this debate by introducing additional data and analysis, with the expectation that increasing our fundamental understanding of this relationship will lead to an ability to predict and tailor the defect-chemistry of ceria-based materials for practical applications. 

Classic chemical sensors integrated in phones, vehicles, and industrial plants monitor the levels of humidity or carbonaceous/oxygen species to track environmental changes. Current projections for the next two decades indicate the strong need to increase the ability of sensors to sense a wider range of chemicals for future electronics not only to continue monitoring environmental changes but also to ensure the health and safety of humans. To achieve this goal, more chemical sensing principles and hardware must be developed. Here, a proof‐of‐principle for the specific electrochemistry, material selection, and design of a Li‐garnet Li₇La₃Zr₂O₁₂(LLZO)‐based electrochemical sensor is provided, targeting the highly corrosive environmental pollutant sulfur dioxide (SO₂). This work extends the prime use of LLZO as a battery component as well as the range of trackable pollutants for potential future sensor‐noses. Novel composite sensing‐electrode designs using LLZO‐based porous scaffolds are employed to define a high number of reaction sites, and successfully track SO₂at the dangerous levels of 0–10 ppm with close‐to‐theoretical SO₂sensitivity. The insights on the sensing electrochemistry, phase stability and sensing electrode/Li⁺electrolyte structures provide first guidelines for future Li‐garnet sensors to monitor a wider range of environmental pollutants and toxins.

 

Next‐generation implantable devices such as sensors, drug‐delivery systems, and electroceuticals require efficient, reliable, and highly miniaturized power sources. Existing power sources such as the Li–I₂pacemaker battery exhibit limited scale‐down potential without sacrificing capacity, and therefore, alternatives are needed to power miniaturized implants. This work shows that ceramic electrolytes can be used in potentially implantable glucose fuel cells with unprecedented miniaturization. Specifically, a ceramic glucose fuel cell—based on the proton‐conducting electrolyte ceria—that is composed of a freestanding membrane of thickness below 400 nm and fully integrated into silicon for easy integration into bioelectronics is demonstrated. In contrast to polymeric membranes, all materials used are highly temperature stable, making thermal sterilization for implantation trivial. A peak power density of 43 µW cm⁻², and an unusually high statistical verification of successful fabrication and electrochemical function across 150 devices for open‐circuit voltage and 12 devices for power density, enabled by a specifically designed testing apparatus and protocol, is demonstrated. The findings demonstrate that ceramic‐based micro‐glucose‐fuel‐cells constitute the smallest potentially implantable power sources to date and are viable options to power the next generation of highly miniaturized implantable medical devices.

 

Enhanced ionic mobility in mixed ionic and electronic conducting solids contributes to improved performance of memristive memory, energy storage and conversion, and catalytic devices. Ionic mobility can be significantly depressed at reduced temperatures, for example, due to defect association and therefore needs to be monitored. Measurements of ionic transport in mixed conductors, however, proves to be difficult due to dominant electronic conductivity. This study examines the impact of different levels of quenched‐in oxygen deficiency on the oxygen vacancy mobility near room temperature. A praseodymium doped ceria (Pr_0.1Ce_0.9O_2–δ) film is grown by pulsed laser deposition and annealed in various oxygen partial pressures to modify its oxygen vacancy concentration. Changes in film non‐stoichiometry are monitored by tracking the optical absorption related to the oxidation state of Pr ions. A 13‐fold increase in ionic mobility at 60 °C for increases in oxygen non‐stoichiometry from 0.032 to 0.042 is detected with negligible changes in migration enthalpy and large changes in pre‐factor. Several factors potentially contributing to the large pre‐factor changes are examined and discussed. Insights into how ionic defect concentration can markedly impact ionic mobility should help in elucidating the origins of variations seen in nanoionic devices.

 

The introduction of new, safe, and reliable solid‐electrolyte chemistries and technologies can potentially overcome the challenges facing their liquid counterparts while widening the breadth of possible applications. Through tech‐historic evolution and rationally analyzing the transition from liquid‐based Li‐ion batteries (LIBs) to all‐solid‐state Li‐metal batteries (ASSLBs), a roadmap for the development of a successful oxide and sulfide‐based ASSLB focusing on interfacial challenges is introduced, while accounting for five parameters: energy density, power density, longterm stability, processing, and safety. First taking a strategic approach, this review dismantles the ASSLB into its three major components and discusses the most promising solid electrolytes and their most advantageous pairing options with oxide cathode materials and the Li metal anode. A thorough analysis of the chemical, electrochemical, and mechanical properties of the two most promising and investigated classes of inorganic solid electrolytes, namely oxides and sulfides, is presented. Next, the overriding challenges associated with the pairing of the solid electrolyte with oxide‐based cathodes and a Li‐metal anode, leading to limited performance for solid‐state batteries are extensively addressed and possible strategies to mitigate these issues are presented. Finally, future perspectives, guidelines, and selective interface engineering strategies toward the resolution of these challenges are analyzed and discussed.

 

Memristive devices are hardware components for applications in neuromorphic computing, memories, and logic computation. This work contributes to the ongoing debate on the switching mechanism of eightwise polarity in SrTiO₃‐based resistive switches. Specifically the effect of atmospheric humidity on the materials defect chemistry and switching properties is considered. Asymmetric devices are designed by exchanging the top and bottom positions of Pt and LaNiO₃electrodes allowing for a separate analysis of the top and the bottom metal‐oxide interfaces. Under dry atmospheres the switching hysteresis is enhanced with a top Pt contact and suppressed with a bottom Pt contact. It is argued that the buried position and dense microstructure of the bottom platinum impedes an oxygen vacancy driven switching mechanism. Under humid atmospheres eightwise switching occurs in both devices suggesting the presence of two switching mechanisms within the same eightwise switching polarity, namely, oxygen vacancy and hydroxide ion enabled switching. The findings help develop strategies to suppress eightwise switching by burying the active metal‐oxide interface and ensuring dense electrode microstructures. Suppression of switching mechanisms relying on exchange with the environment is desirable for technological implementation of resistive switches and for strategies in stacking of memristive devices for memory and for neuromorphic hardware.

 

Memristive devices are among the most prominent candidates for future computer memory storage and neuromorphic computing. Though promising, the major hurdle for their industrial fabrication is their device‐to‐device and cycle‐to‐cycle variability. These occur due to the random nature of nanoionic conductive filaments, whose rupture and formation govern device operation. Changes in filament location, shape, and chemical composition cause cycle‐to‐cycle variability. This challenge is tackled by spatially confining conductive filaments with Ni nanoparticles. Ni nanoparticles are integrated on the bottom La_0.2Sr_0.7Ti_0.9Ni_0.1O_3−δelectrode by an exsolution method, in which, at high temperatures under reducing conditions, Ni cations migrate to the perovskite surface, generating metallic nanoparticles. This fabrication method offers fine control over particle size and density and ensures strong particle anchorage in the bottom electrode, preventing movement and agglomeration. In devices based on amorphous SrTiO₃, it is demonstrated that as the exsolved Ni nanoparticle diameter increases up to≈50 nm, the ratio between the ON and OFF resistance states increases from single units to 180 and the variability of the low resistance state reaches values below 5%. Exsolution is applied for the first time to engineer solid–solid interfaces extending its realm of application to electronic devices.

 

Effective integration of perovskite films into devices requires knowledge of their electro‐chemomechanical properties. Raman spectroscopy is an excellent tool for probing such properties as the films' vibrational characteristics couple to the lattice volumetric changes during chemical expansion. While lattice volumetric changes are typically accessed by analyzing Raman shifts as a function of pressure, stress, or temperature, such methods can be impractical for thin films and do not capture information on chemical expansion. An in situ Raman spectroscopy technique using an electrochemical titration cell to change the oxygen nonstoichiometry of a model perovskite film, Sr(Ti,Fe)O_3−y , is reported and the lattice vibrational properties are correlated to the material's chemical expansion. How to select an appropriate Raman vibrational mode to track the evolution in oxygen nonstoichiometry is discussed. Subsequently, the frequency of the oxygen stretching mode around Fe⁴⁺is tracked, as it decreases during reduction as the material expands and increases during reoxidation as the material shrinks. This methodology of oxygen pumping and in situ Raman spectroscopy of oxide films enables future in operando measurements even for small material volumes, as is typical for applications of films as electrodes or electrolytes utilized in electrochemical energy conversion or memory devices.