SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-026-4288-1
The high-temperature oxidation resistance of Cr2AlC MAX phase ceramics is severely compromised by rapid Al depletion and the formation of a brittle sub-surface Cr7C3 layer. This study elucidates how trace Y2O3 doping (0.25 and 0.5 wt.%) modulates the oxidation behavior of Cr2AlC at 1100 °C. The incorporation of 0.5 wt.% Y2O3 significantly suppresses the parabolic rate constant compared to undoped counterparts. This kinetic suppression is attributed to the Reactive Element Effect (REE), where Y3+ segregation at α-Al2O3 grain boundaries inhibits outward Al3+ diffusion, shifting the scale growth mechanism to inward oxygen diffusion control. Consequently, this retarded Al consumption prevents the decomposition of the Cr2AlC substrate into Cr7C3. While undoped specimens fail due to volume contraction and Kirkendall voiding associated with the Cr7C3 interlayer, specimens with the most effective doping content within the investigated range maintain a stable, atomically sharp α-Al2O3/Cr2AlC interface devoid of voids and decomposition products. The superior adhesion of this interface is attributed to three synergistic factors: the elimination of volumetric mismatch induced by phase transformation, the mechanical interlocking provided by Y-rich oxide pegs, and the intrinsically higher interfacial bonding strength of the α-Al2O3/Cr2AlC system as confirmed by DFT calculations. These findings provide a mechanistic framework for designing oxidation-resistant MAX phase ceramics via reactive element doping.
SCIENCE CHINA Materials•2026•DOI: 10.1007/s40843-025-3728-5
Biological intelligence achieves exceptional energy efficiency and environmental adaptability, exemplified by the human brain's ~20 W resting power consumption. A key strategy is the use of multi-ions as signal carriers for transduction and processing. Iontronics, employing ions instead of electrons, offer a promising route to low-energy, heat-dissipation-free devices for memory, sensing, and neuromorphic computing. However, conventional iontronics require external voltage bias to drive ion motion, complicating miniaturization and integration. Here, we highlight a recent breakthrough by Guo et al. reporting a bias-free iontronic memory sensor ('memsensor') that operates by controlling surface ion migration. The device couples vanadium dioxide (VO2) with a low-work-function indium (In) patch. Upon immersion in NaCl solution, In3+ ions generated electrochemically within the Debye length are driven by the intrinsic surface electric field to diffuse into the VO2 surface, inducing an insulator-to-metal phase transition and a measurable, non-volatile change in surface conductance. This conductance state correlates with NaCl concentration and can be reversibly restored by H2O2 treatment. The memsensor emulates the gustatory plasticity of C. elegans, mimicking the response dynamics of ASEL and ASER neurons. In a proof-of-concept, a model boat equipped with the memsensor exhibits adaptive chemotaxis: after 'starvation' training in high NaCl concentration, it avoids high-concentration zones; conversely, after training in low concentration, it migrates toward high-concentration zones. This work demonstrates a bias-free strategy for programmable memory and sensing, potentially advancing autonomous microsystems and bioinspired electronics.
Environmental Chemistry•2026•DOI: 10.7524/j.issn.0254-6108.2025031905
Land use types profoundly influence the accumulation, speciation, and ecological risk of heavy metals through differences in human activity intensity, pollution input pathways, and soil self-regulation capacity. This study investigated soils of different land use types in Longhua County, downstream of the Yixun River Basin, central Chengde City, Hebei Province. Using the Nemerow Index and Potential Ecological Risk Index, the overall regional pollution was mild (Pn=1.65) with low ecological risk (RI=121.17). Main pollutants were Cd, Pb, Zn, and Hg, with Cd and Hg as primary ecological risk factors. Construction land exhibited moderate pollution and medium risk, with a Nemerow Index of 2.37 and average RI of 190.78, significantly exceeding other land use types. PMF model identified four pollution sources: pedogenic parent material natural source (43.54% contribution) dominating Cr, Cu, Ni, Zn enrichment; metallogenic parent material natural source (19.88%) controlling Cd spatial differentiation; agricultural-transportation mixed source (24.79%) driving As and Pb accumulation; and industrial source (11.93%) causing local Hg enrichment. Natural sources contributed 63.42% of total heavy metals, being the primary contributor. As was generally below background values, not constituting pollution; Pb exceeded standards but posed low ecological risk; industrial Hg enrichment in construction land presented high pollution and ecological risk, requiring priority control.