Multi-Cationic Aluminate Spinels With Vacancy-Stabilized Entropy
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Solution Overview
Problem
Existing high entropy oxides (HEOs) are limited by stoichiometric crystal structures with a single equivalent cationic site, restricting the design of unique complex oxides and lacking systematic study of high vacancy concentrations, which are crucial for enhancing properties like ionic conductivity and catalytic activity.
Innovation Solution
Development of multi-cationic aluminate spinels with at least three different divalent metal cations in nominally equimolar concentrations, incorporating cationic and anionic vacancies to stabilize the spinel structure, allowing for increased configurational entropy and tunable structural, chromatic, and chemical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If stoichiometric crystal structures with a single equivalent cationic site are used, then the crystal structure is simple and easy to synthesize, but the number of design parameters is limited and unique complex oxide properties cannot be achieved
Solution Approach 1:
The single cationic site is segmented into multiple distinct cationic sites (tetrahedral A-sites and octahedral B-sites), allowing independent occupation by different cations. This segmentation enables unique complex oxide properties by permitting diverse cation arrangements while maintaining the spinel crystal structure framework.
Solution Approach 2:
The invention creates composite multi-cationic aluminate spinels by combining at least three different divalent metal cations (e.g., Ni, Co, Mn, Cu, Zn, Mg, Ca) within the spinel structure. This composite approach allows tuning of structural, chromatic, and chemical properties through selective cation placement on different sites, resolving the contradiction between design flexibility and structural complexity.
2Reliability
If high vacancy concentrations are introduced to enhance ionic conductivity and catalytic activity, then the material properties are improved, but the structural stability becomes compromised
Solution Approach 1:
Vacancies are strategically distributed at specific crystallographic sites (A-sites and/or B-sites) rather than uniformly throughout the structure. This local quality approach allows enhancement of ionic conductivity and catalytic activity at vacancy-rich regions while maintaining structural stability in vacancy-poor regions through the presence of stabilizing cations.
Solution Approach 2:
The invention systematically varies vacancy concentration as a compositional parameter within controlled ranges (e.g., x in MxAl2-xO4 where 0 < x < 2). By treating vacancy concentration as a tunable parameter rather than a fixed defect, the material achieves optimal balance between enhanced properties and structural stability through precise compositional control.
3Stability of the object's composition
If conventional high temperature processing is used to form phase pure spinels, then the structural stability is ensured, but the processing energy consumption increases and material properties may be degraded
Solution Approach 1:
The spinel precursors are pre-synthesized using low-temperature sol-gel or co-precipitation methods, creating homogeneous mixed-metal oxide precursors with controlled composition and nanoscale morphology. This preliminary action ensures uniform cation distribution and reactive surface area, enabling subsequent phase-pure spinel formation at reduced temperatures (e.g., 900-1100°C instead of conventional 1200-1400°C) while maintaining structural stability.
Solution Approach 2:
The multi-cationic composition acts as a self-stabilizing composite system where the combined presence of multiple cations (e.g., Ni, Co, Mn, Cu, Zn, Mg, Ca) creates synergistic effects that lower the processing temperature required for phase-pure spinel formation. The composite nature of the material enables reduced energy consumption while ensuring structural stability through the collective stabilization provided by different cation-oxygen bond strengths and ionic radii.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-cationic aluminate spinels achieve phase pure complex oxides at lower processing temperatures, enabling enhanced catalytic performance and a wider range of applications as pigments, photo absorbents, and catalysts, with regenerable catalysts for methane dry reforming.
Implementation Method 1
These structures are stabilized through configurational entropy (Sc), which increases with the number of unique arrangements of cations and anions within the crystal structure according to Equation 1
Implementation Method 2
The tendency of constituent cations to adopt dissimilar secondary oxide phases is overcome when increased entropy outweighs enthalpic energy penalties associated with mixing, according to the Gibbs equation (ΔG=ΔH−TΔS)
Implementation Method 3
comprising providing the Ni-based multi-cationic aluminate spinel catalyst, and exposing a stream comprising methane and carbon dioxide to the Ni-based multi-cationic aluminate spinel catalyst at an elevated temperature, thereby catalytically reacting the methane and carbon dioxide to produce a synthesis gas
Implementation Method 4
The exposed, spent Ni-based multi-cationic aluminate spinel catalyst can be regenerated under oxidizing conditions
Data Source
AI summary
The present invention is directed to both stoichiometric and sub-stoichiometric high entropy aluminate spinels as a novel high entropy oxide (HEO) crystal phase. Previously reported HEOs are overwhelmingly stoichiometric structures containing a single cationic site and are stabilized solely by intermixing increasing numbers of cations. According to an aspect of the invention, sub-stoichiometric spinels, containing various mixtures of divalent metal cations and cationic vacancies in nominally equimolar concentration, provide entropic stabilization similarly to cations in stoichiometric spinels. The chromatic, structural, and chemical properties of these complex spinels are highly tunable via incorporation of cationic vacancies and multiple divalent metals, enabling their application as unique pigments, catalysts, and thermal coatings.