Enhanced yield synthesis of bulk dense (M_2/3Y_1/3)₂AlC (M = Cr, W, Mo) in-plane chemically ordered quaternary atomically laminated i-MAX phases and oxidation of (Cr_2/3Y_1/3)₂AlC and (Mo_2/3Y_1/3)₂AlC

Recently, a new family of MAX phases with in-plane chemical order, i-MAX, have been discovered which incorporate new elements expanding the family of MAX phases. i-MAX phases remain to be synthesized in single-phase bulk form for characterization. Herein, we show that by reactively hot pressing an intermetallic precursor, Y_2.23Al, instead of elemental Y, in combination with excess overall Al and a sub-stoichiometric fraction of carbon, we enhance the yield of (Cr_2/3Y_1/3)₂AlC to 85±3 wt% (86±3 mol%). Both the fractions of the impurity Y₂O₃ phase and the undesirable ternary Cr₂AlC are reduced. Subsequent isothermal oxidation of (Cr_2/3Y_1/3)₂AlC in natural air in the 1000–1400 °C temperature range reveals the formation of Y₃Al₂(AlO₄)₃ (YAG), Cr₂O₃ and Y₂O₃, without a continuous Cr₇C₃ sub-layer. Additionally, we show that by starting with Y_2.23Al reagent we synthesize dense bulk (W_2/3Y_1/3)₂AlC and (Mo_2/3Y_1/3)₂AlC samples with enhanced i-MAX yields of 72±3 wt% (59±2 mol%) and 91±3 wt% (72±2 mol%), respectively. Oxidation of (Mo_2/3Y_1/3)₂AlC at 1300 °C for 12 h leads to formation of a thick, porous oxide of Y₂Mo₃O₁₂.