The structural, elastic, electronic, thermal, and optical properties of superconducting nanolaminates Ti2InX (X？=？C, N) are investigated by density functional theory (DFT). The results obtained from the least studied nitride phase are discussed in comparison with those of carbide phase having value half as that of the former. The carbide phase is found to be brittle in nature, while the nitride phase is less brittle. Elastic anisotropy demonstrates that the c-axis is stiffer in Ti2InN than in Ti2InC. The band structure and density of states show that these phases are conductors, with contribution predominantly from the Ti 3d states. The bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient are obtained as a function of temperature and pressure for the first time through the quasiharmonic Debye model with phononic effects. The estimated values of electron-phonon coupling constants imply that Ti2InC and Ti2InN are moderately coupled superconductors. The calculated thermal expansion coefficient is in fair agreement with the only available measured value for Ti2InC. Further the first time calculated optical functions reveal that the reflectivity is high in the IR-visible-UV region up to？~10？eV and 12.8？eV for Ti2InC and Ti2InN, respectively, showing these to be promising coating materials. 1. Introduction The so-called nanolaminates (or MAX) phases since their discovery by Nowotny [1] have attracted a lot of interest among the research community due to their remarkable properties having attributes of both ceramic and metal [2–24]. Ceramic attributes include lightweight, elastically rigid, and high temperatures strength, whereas metallic attributes show the phases to be thermally and electrically conductive, quasiductile, and damage tolerant. Currently there are about 60 synthesized MAX phases [3]. Out of these only seven low- superconductors have so far been identified. These are Mo2GaC [4], Nb2SC [5], Nb2SnC [6], Nb2AsC [7], Ti2InC [8], Nb2InC [9], and Ti2InN [10]. The X-ray diffraction, magnetic, and resistivity measurements discovered that Ti2InX (X = C, N) are superconductors [8, 10] with superconducting temperatures of 3.1 and 7.3？K, respectively. In fact Bortolozo et al. [10] in 2010 showed unambiguously that Ti2InN is the first nitride superconductor belonging to the family. Among the ternary phases almost all the studies are concerned with carbide properties, but a very limited work on nitrides which was discovered in 1963 by Jeitschko et al. [12]. This nitride crystallizes in the same prototype structure as carbides
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