Chloride‐Ion‐Stabilized Strontium Mayenite: Expansion of Versatile Material Family

Abstract

Sr‐mayenite (S12A7) incorporating Cl− ions in its crystallographic cages up to the theoretical maximum occupancy, Sr12Al14O32Cl2, is reported in our study. The addition of a stoichiometric amount of SrCl2 to the starting mixture is effective for the formation of Sr12Al14O32Cl2 with high phase purity. Almost 100% densification is achieved using spark plasma sintering (SPS). Evaporation of SrCl2 from Sr12Al14O32Cl2, which becomes significant at sintering temperatures above ~1300°C, degrades the phase purity. However, SrCl2 effusion is significantly suppressed in the samples fully densified by SPS, impeding the decomposition of Sr12Al14O32Cl2 up to temperature as high as ~1400°C. The crystal structure of Sr12Al14O32Cl2 was investigated by Rietveld analysis of the X‐ray diffraction pattern. It is found that the Cl− ion is incorporated in the center of the inner cage with nearly theoretical maximum occupancy, which is responsible for the phase stability. Porous Sr12Al14O32Cl2 exhibits humidity‐sensitive surface protonic conductivity. Dense Sr12Al14O32Cl2 prepared under reducing conditions such as SPS exhibits electronic conductivity. Sr‐mayenite has various potential applications derived from its multifunctionalities.

High‐pressure synthesis of a 12CaO·7Al2O3–12SrO·7Al2O3 solid solution

“…Thus, one hypothesis for the sudden conductivity enhancement in the x =0 sample (S12A7) is a result of this interstitial (direct) diffusion occurring, which provides a fast ionic conduction. As described above, it is known that bulk ionic conductivity of C12A7 is sensitive to the preparation procedure as well as measurement conditions . From the viewpoint of a physicochemical analogy between C12A7 and S12A7, further optimization of S12A7 conductivity at lower temperature (<600°C) may be possible by applying a similar analogy that was efficient for improving conductivity of C12A7.…”

“…reported that incorporation of OH − ions in C12A7 and S12A7 induces a cage distortion as a displacement of a calcium or strontium ion toward anions located at the cage . On the other hand, Cl − ‐ion‐encaged S12A7 shows no cation displacement, presumably because the ionic radius fits the cage size . From this aspect, control of cage size is anticipated to be effective as a way to incorporate a new anion with various ionic radii because stability of the accommodated ions is considered to be related with cage size.…”

Fe-doped mayenite electride composite with 2D reduced Graphene Oxide: As a non-platinum based, highly durable electrocatalyst for Oxygen Reduction Reaction

“…2). From 100–150 °C, weight loss were observed by physically absorb water and dehydration reaction of crystal water in the nitrates evaporates 17 , and small endothermic peak confirmed the first citric acid decomposition below the 200 °C, where all citrate conversion after decomposition did not occurs into gaseous products due to the decomposition of nitrate under inert gas environment 18 . The brownish color of gel also confirmed the contamination of precursors by high amount of the unburned carbon 1,5,7 .…”

Novel Two-Dimensional Carbon–Chromium Nitride-Based Composite as an Electrocatalyst for Oxygen Reduction Reaction

“…The TGA causes phase transformation through the exothermic or endothermic process in the N 2 -gas environment from 30 to 1,100°C (Figure 2). The first weight loss was about 5%, which came into view possibly because of the physical absorption and because dehydrated crystalline water in the nitrates evaporated at about 100–150°C along with decomposition of precursor nitrides (Dong et al, 2014).…”