A progress report on the MAB phases: atomically laminated, ternary transition metal borides KotaSankalp SokolMaxim BarsoumMichel W. 2019 <p>The MAB phases are atomically layered, ternary or quaternary transition metal (M) borides (TMBs), with the general formula (MB)<sub>2<i>z</i></sub>A<i><sub>x</sub></i>(MB<sub>2</sub>)<i><sub>y</sub></i> (<i>z</i> = 1–2; <i>x</i> = 1–2; <i>y</i> = 0–2), whose structures are composed of a transition M-B sublattices interleaved by A-atom (A = Al,Zn) mono- or bilayers. Most of the MAB phases were discovered before the 1990s, but recent discoveries of intriguing magnetocaloric properties, mechanical deformation behaviour, catalytic properties, and high-temperature oxidation resistance has led to their ‘re-discovery’. Herein, MAB phase synthesis is reviewed and their magnetic, electronic, thermal, and mechanical properties are summarized. Because the M-B layers in the MAB phases structurally resemble their corresponding binaries of the same M:B stoichiometry, the effects of the A-layers on properties are discussed. Inconsistencies in the literature are critically assessed to gain insights on the processing-structure-property relations, suggest fruitful avenues for future research, and identify limitations for prospective applications.</p>