Mechanical properties consisting of the bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, etc., are key factors in determining the practical applications of MAX phases. These mechanical properties are mainly dependent on the strength of M-X and M-A bonds. In this study, a novel strategy based on the crystal graph convolution neural network (CGCNN) model has been successfully employed to tune these mechanical properties of Ti₃AlC₂-based MAX phases via the A-site substitution (Ti₃(Al_1−xA_x)C₂). The structure—property correlation between the A-site substitution and mechanical properties of Ti₃(Al_1−xA_x)C₂ is established. The results show that the thermodynamic stability of Ti₃(Al_1−xA_x)C₂ is enhanced with substitutions A = Ga, Si, Sn, Ge, Te, As, or Sb. The stiffness of Ti₃AlC₂ increases with the substitution concentration of Si or As increasing, and the higher thermal shock resistance is closely associated with the substitution of Sn or Te. In addition, the plasticity of Ti₃AlC₂ can be greatly improved when As, Sn, or Ge is used as a substitution. The findings and understandings demonstrated herein can provide universal guidance for the individual synthesis of high-performance MAX phases for various applications.

Rare-earth phosphates (REPO₄) are regarded as one of the promising thermal/environmental barrier coating (T/EBC) materials for SiC_f/SiC ceramic matrix composites (SiC-CMCs) owing to their excellent resistance to water vapor and CaO-MgO-Al₂O₃-SiO₂ (CMAS). Nevertheless, relatively high thermal conductivity of REPO₄ becomes the bottleneck for their practical application. In this work, novel xenotime‑type high entropy (Dy_1/7Ho_1/7 Er_1/7Tm_1/7Yb_1/7Lu_1/7Y_1/7)PO₄ (HE (7RE_1/7)PO₄) has been designed and synthesized for the first time to solve this issue. HE (7RE_1/7)PO₄ with a homogeneous rare-earth element distribution exhibits high thermal stability up to 1750 °C and good chemical compatibility with SiO₂ up to 1400 °C. In addition, the thermal expansion coefficient (TEC) of HE (7RE_1/7)PO₄ (5.96 × 10^-6/°C at room temperature to 900 °C) is close to that of SiC-CMCs. What’s more, the thermal conductivity of HE (7RE_1/7)PO₄ (from 4.38 W·m^-1 K^-1 at 100 °C to 2.25 W·m^-1 K^-1 at 1300 °C) is significantly decreased compared to those of single-component REPO₄ with the minimum value ranging from 9.90 to 4.76 W·m^-1·K^-1. These results suggest that HE (7RE_1/7)PO₄ has the potential to be applied as T/EBC material for SiC-CMCs in the future.

Sn doping is usually adopted to prepare Ti₃AlC₂ in mass production because it can reduce the synthesis temperature while increasing the phase purity. However, excessive Sn doping usually deteriorates the oxidation resistance of Ti₃AlC₂. Therefore, an appropriate Sn doping concentration is a vital issue. In this work, the effect of Sn doping concentration on the oxidation behavior of Ti₃AlC₂ was systematically investigated by combining theoretical calculations and experimental methods. Density function theory calculations suggest that the oxygen adsorption mechanisms for the (001) surface of Ti₃AlC₂ with and without Sn doping are similar, and Ti-O bonds are always preferentially formed. The molecular dynamics simulation further indicates that Al atoms have a faster diffusion rate during the oxidation process. Therefore, a continuous Al₂O₃ layer can form rapidly at high temperature. Nevertheless, when the Sn doping concentration exceeds 10 mol%, the continuity of the Al₂O₃ layer is destroyed, thereby impairing the oxidation resistance of Ti₃AlC₂. Furthermore, oxidation experiments verify the above results. The oxidation mechanisms of Ti₃AlC₂ with different Sn doping concentrations are also proposed.

The development of bifunctional electrocatalysts with efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is still a key challenge at the current stage. Herein, FeNi LDH/V₂CT_x/nickel foam (NF) self-supported bifunctional electrode was prepared via deposition of FeNi LDH on V₂CT_x/NF substrate by hydrothermal method. Strong interfacial interaction between V₂CT_x/NF and FeNi LDH effectively prevented the aggregation of FeNi LDH, thus exposing more catalytic active sites, which improved electrical conductivity of the nanohybrids and structural stability. The results indicated that the prepared FeNi LDH/V₂CT_x/NF required 222 mV and 151 mV overpotential for OER and HER in 1 M KOH to provide 10 mA cm⁻², respectively. Besides, the FeNi LDH/V₂CT_x/NF electrocatalysts were applied to overall water splitting, which achieved a current density of 10 mA cm⁻² at 1.74 V. This work provides ideas for improving the electrocatalytic performance of electrocatalysts through simple synthesis strategies, structural adjustment, use of conductive substrates and formation of hierarchical structures.