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In compositionally complex materials, there is controversy on the effect of enthalpy versus entropy on the structure and short-range ordering in so-called high-entropy materials. To help address this controversy, we synthesized and probed 40 M4AlC3 layered carbide phases containing 2 to 9 metals and found that short-range ordering from enthalpy is present until the entropy increases enough to achieve complete disordering of the transition metals in their atomic planes. We transformed all these layered carbide phases into two-dimensional (2D) sheets and showed the effects of the order vs. disorder on their surface properties and electronic behavior. This study suggests the key effect that the competition between enthalpy and entropy has on short-range order in multi-compositional materials. 

Abstract To advance the MXene field, it is crucial to optimize each step of the synthesis process and create a detailed, systematic guide for synthesizing high‐quality MXene that can be consistently reproduced. In this study, a detailed guide is provided for an optimized synthesis of titanium carbide (Ti₃C₂T_x) MXene using a mixture of hydrofluoric and hydrochloric acids for the selective etching of the stoichimetric‐Ti₃AlC₂MAX phase and delamination of the etched multilayered Ti₃C₂T_xMXene using lithium chloride at 65 °C for 1 h with argon bubbling. The effect of different synthesis variables is investigated, including the stoichiometry of the mixed powders to synthesize Ti₃AlC₂, pre‐etch impurity removal conditions, selective etching, storage, and drying of MXene multilayer powder, and the subsequent delamination conditions. The synthesis yield and the MXene film electrical conductivity are used as the two parameters to evaluate the MXene quality. Also the MXenes are characterized with scanning electron microscopy, x‐ray diffraction, atomic force microscopy, and ellipsometry. The Ti₃C₂T_xfilm made via the optimized method shows electrical conductivity as high as ≈21,000 S/cm with a synthesis yield of up to 38 %. A detailed protocol is also provided for the Ti₃C₂T_xMXene synthesis as the supporting information for this study.