Lithium and sodium (Na) mixed polyanion solid electrolytes for all-solid-state batteries display some of the highest ionic conductivities reported to date. However, the effect of polyanion mixing on the ion-transport properties is still not fully understood. Here, we focus on Na1+xZr2SixP3−xO12 (0 ≤ x ≤ 3) NASICON electrolyte to elucidate the role of polyanion mixing on the Na-ion transport properties. Although NASICON is a widely investigated system, transport properties derived from experiments or theory vary by orders of magnitude. We use more than 2000 distinct ab initio-based kinetic Monte Carlo simulations to map the compositional space of NASICON over various time ranges, spatial resolutions and temperatures. Via electrochemical impedance spectroscopy measurements on samples with different sodium content, we find that the highest ionic conductivity (i.e., about 0.165 S cm–1 at 473 K) is experimentally achieved in Na3.4Zr2Si2.4P0.6O12, in line with simulations (i.e., about 0.170 S cm–1 at 473 K). The theoretical studies indicate that doped NASICON compounds (especially those with a silicon content x ≥ 2.4) can improve the Na-ion mobility compared to undoped NASICON compositions.

The development of inexpensive batteries based on magnesium (Mg) chemistry will contribute remarkably toward developing high-energy-density storage systems that can be used worldwide. Significant challenges remain in developing practical Mg batteries, the chief of which is designing materials that can provide facile transport of Mg. In this review, we cover the experimental and theoretical methods that can be used to quantify Mg mobility in a variety of host frameworks, the specific transport quantities that each technique is designed to measure or calculate, and some practical examples of their applications. We then list the unique challenges faced by different experimental and computational techniques in probing Mg ion transport in materials. This review concludes with an outlook on the directions that the scientific community could soon pursue as we strive to construct a pragmatic Mg battery. Expected final online publication date for the Annual Review of Materials Research, Volume 52 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Realization of fully solid-state white light emitting devices requires high efficiency blue, green, and red emitters. However, challenges remain in boosting the low quantum efficiency of long wavelength group-III-nitride light emitters through conventional quantum well growth. Here, we demonstrate a new direct metal−organic chemical vapor deposition approach to grow In-rich InGaN quantum dots on Si substrates using V-pits, bypassing the need for patterning or unconventional substrates. A correlative nanoscale study on the optical, compositional, and structural properties of intersecting V-pits reveals that the highly textured surface gives rise to localized high intensity red-shifted emission from the apexes of pyramids where InGaN quantum dots spontaneously form. We establish the origin of this efficient long wavelength luminescence to result from both spatially confined higher In-content deposition, as well as smaller bandgap energy basal stacking faults entrapped within a ring of low-emissivity prismatic stacking faults. Our monolithic growth approach on Si would open up new pathways toward attaining CMOS-compatible phosphor-free white light emitting solid-state devices.