CALPHAD databases have traditionally been developed for investigation of single-principal component alloys. With the advent of batch processing capability, engineering teams have proposed using these models to systematically explore compositional space for multiprincipal element systems. However, the uncertainty of phase equilibria predictions outside of traditional compositional bounds has yet to be evaluated. This study assesses the current capabilities of commercially available CALPHAD databases to predict phase equilibria within ternary phase space as a function of the number of full binary system descriptions contained within the thermodynamic databases, the spatial location in compositional space relative to subsystem descriptions, and the specific database used. A strong correlation was observed between the fraction of subsystem descriptions available for the free energy calculation and the accuracy of phase predictions in undefined ternary space. The accuracy of equilibria predictions degraded with increased compositional extrapolation from defined subsystems.

Unique SnO2 monoflowers with an aloe-like morphology were successfully synthesized via a one-step hydrothermal method. The structural, chemical, and physical characteristics were investigated. The results exhibited that the as-prepared sample was assembled by triangle rutile SnO2 nanoslices with rough surfaces. A possible crystal growth and nanostructure assembling mechanism was proposed. The Raman peaks in 171, 235, and 211 cm−1 proved that a large amount of oxygen defects existed inside the sample, which might narrow the band gap from 3.6 eV of pure SnO2 to 2.7 eV of the sample. The sensor fabricated by aloe-like SnO2 nanostructures exhibited an excellent response and selectivity to ethanol. The developed sensor can detect ethanol as low as 10 ppm at 360 °C. The prepared aloe-like SnO2 microflower sensor exhibited a gas sensing response of about 7.46 when exposed to 100 ppm of ethanol gas at 360 °C, which was probably related to more numerous defects and thinner structure of aloe-like SnO2.

The microstructure evolution and mechanical properties of Mg–10Gd–3Y–xZn–0.6Zr (x = 0.5, 1, and 1.5 wt%) alloys in the as-cast, solution-treated, and peak-aged conditions have been investigated systematically. The results indicate that the microstructure of the as-cast alloy with 0.5% Zn consists of α-Mg, (Mg,Zn)3RE and Mg24(RE,Zn)5 phases, while the alloy with 1.0 and 1.5% Zn consists of α-Mg, (Mg,Zn)3RE and some stacking faults. Moreover, 18R-LPSO phases are observed in the as-cast alloy with 1.5% Zn. The formation of LPSO phases involves not only stacking sequence ordered but also chemical composition ordered. After solution treatment, the Mg24(RE,Zn)5, (Mg,Zn)3RE, stacking faults, and 18R-LPSO phases transform into 14H-LPSO phases. The 14H-LPSO phase plays an important role in the improvement of mechanical properties, especially for the ductility. The β′ phase with a bco structure precipitates in the peak-aged alloys results in precipitation hardening, significantly improving the tensile strength, but it leads to poor ductility.

Rational design of bio-hybrid photovoltaic and/or optoelectronic devices requires systematic electrochemical characterizations of photosystem I (PSI), the photosynthetic membrane protein, assembled onto tailored biotic–abiotic interfaces. This work communicates our research findings on the role of PSI microenvironment alterations at organic/inorganic interfaces, via biomimetic lipid membrane confinements and plasmonic coupling with Ag nano-pyramid structures, in tuning the photoactivated charge separation and photocurrent generations from surface-assembled PSI. The observed photocurrent enhancements and the associated mechanistic insights from this study will facilitate the future design of tailored interfaces that can optimally tune the photoactivity and photostability of PSI in solid-state bioelectronics.

Three different hydrothermally grown carbonaceous materials and their molybdenum chalcogenides derived from glucose (HTC, HTC–MoO2, HTC–MoS2) were investigated to evaluate their potential as Li-ion battery anodes. All tested materials exhibited good cycling performance at a current density of 100 mA/g and showed high coulombic efficiency, >98%, after the 50th cycle. Reversible charge capacities of HTC, HTC–MoO2, and HTC–MoS2 were 296, 266, and 484 mAh/g, respectively, after 50 successive cycles. This study demonstrated that the HTC–MoS2 showed the highest reversible charge capacity which promises to be a good candidate for an environmentally friendly anode material for Li-ion batteries.

Atomic clusters attached to a low-dimensional system, called Fano defects, produce rich wave interferences. In this work, we analytically found an enhanced thermoelectric figure-of-merit (ZT) in periodic atomic chains with Fano defects, compared with those without such defects. We further study self-assembled DNA-like systems with periodic and quasiperiodically placed Fano defects by using a real-space renormalization method developed for the Kubo–Greenwood formula, in which tight-binding and Born models are respectively used for the electric and lattice thermal conductivities. The results reveal that the quasiperiodicity could be another ZT-improving factor, whose long-range disorder inhibits low-frequency acoustic phonons insensitive to local defects.

High-density storage technology beyond hard disk drives and flash memory is required. Efforts are underway to develop new high-density storage technology based on scanning probe-based data storage. One of the candidates for scanning probe-type storage is thermomechanical data storage (also known as millipede, developed by IBM Zürich), and another is ferroelectric data storage. In this article, probe data-storage technologies are overviewed. Thermomechanical data storage and ferroelectric data storage are described in detail for next-generation high-density data-storage technology based on scanning probe microscopy. Ferroelectric data storage and scanning nonlinear dielectric microscopy-based and field-effect transistor-type probe-based probe data storage are also described.

Ferroelectrics are promising for nonvolatile memories. However, the difficulty of fabricating ferroelectric layers and integrating them into complementary metal oxide semiconductor (CMOS) devices has hindered rapid scaling. Hafnium oxide is a standard material available in CMOS processes. Ferroelectricity in Si-doped hafnia was first reported in 2011, and this has revived interest in using ferroelectric memories for various applications. Ferroelectric hafnia with matured atomic layer deposition techniques is compatible with three-dimensional capacitors and can solve the scaling limitations in 1-transistor-1-capacitor (1T-1C) ferroelectric random-access memories (FeRAMs). For ferroelectric field-effect-transistors (FeFETs), the low permittivity and high coercive field Ec of hafnia ferroelectrics are beneficial. The much higher Ec of ferroelectric hafnia, however, makes high endurance a challenge. This article summarizes the current status of ferroelectricity in hafnia and explains how major issues of 1T-1C FeRAMs and FeFETs can be solved using this material system.

Nonvolatile memories (NVMs) are key devices in computers to save a user’s information. Besides flash memory, several types of NVMs that use magnetoresistance, resistance change of metal oxides, and phase change of chalcogenide alloys have been studied. Among these, phase-change random-access memory (PC-RAM) is competitive from the viewpoint of switching speed, high durability, and scalability. In 2017, Intel and Micron Technology shipped commercial devices named Optane that use a phase-change material as storage class memories. Condensed-matter physicists have recently been attracted to phase-change materials because of their functionality as topological insulators. If the topological phase state is controllable and applied to PC-RAM, electron spin transfer and storage effects will be further available in addition to electrical resistance switching.

Material development has played a crucial role in modern civilization and IT. The importance of high-density and high-performance memory in modern computer systems and IT is ever increasing. This trend will be more obvious as computational architectures shift from being processing-centric to memory- (or data-) centric. The need for emerging and new memory technologies with nonvolatility and low power-consuming performance is rapidly increasing, while improvements in current dynamic random-access memory and NAND flash are being pursued. In both new and current memories, material innovation is of central importance. In this issue of MRS Bulletin, recent improvements in these two critical fields are reviewed with a focus on emerging and novel materials for the disruptive memory concept. Recent progress in scanning probe-based memory devices is also described.