Ti₂InN is the first nitride in the MAX-phase family (into Cr₂AlC prototype) for which superconductivity was reported A.D. Bortolozo et al. [1]. It was proposed that the substitution of carbon in Ti₂InC for nitrogen increases the superconducting transition temperature from 3.1 K to about 7.3 K due to an increase of the electronic density of states at the Fermi level (E_F) from 3.67 for 4.02 states/(eV cell) [1]. The structure of Ti₂InN in [1] was characterized only by X-ray. X ray pattern showed peaks of in Ti₂InN and the presence of small amount of In. Unfortunately, SEM EDX or TEM studies of the synthesized material were not reported in literature. The Ti₂InN samples of the study by Bortolozo et al. [1] 

In the present study, we prepared samples by different methods. The first two stages of synthesis followed exactly the route described in [1]. The third stage (pressure treatment) was modified. Route1: We repeated the method described in [1] but with 130 bar of nitrogen instead of argon. Route 2: Sintering in Ar in a sealed quartz ampoule. Routes 3, 7 and 8: Spark plasma sintering (SPS) at 38-50 MPa in contact with hBN. Route 4: High pressure-high temperature (HP-HT) sintering under 4 GPa in contact with hBN. Route 5: Repetition of Route 1 after removing air from the furnace more carefully. Using HP-HT, SPS methods and sintering in sealed quartz ampoule in Ar in the third stage (Routes 2, 3, 4, 7 and 8), we succeeded to synthesize Ti₂InN samples containing 85.3-94 wt.% of Ti₂InN (with lattice parameters a=0.3073(7)-0.3078(8) nm, c=1.4012(4)-1.4030(8) nm, unit cell volume V=114.667´10^-3 - 115.114 ´10^-3 nm³ ) which demonstrated superconducting behavior with Tc (onset) near 5 K. The samples prepared by SPS and HP-HT methods were highly dense. However, all samples showed a very broad magnetic transition (as susceptibility) not saturating down to 2 K. No macroscopic Meissner phase was established. The magnetization was far too weak to evidence bulk superconductivity of the entire sample (would require around 30 A/m) and hence of Ti₂InN. The signal stems either from a minority phase, or from surface superconductivity. According to SEM EDX study, the stoichiometry of the Ti₂InN phase of these samples were very close to 211, but in many cases a small excess of nitrogen or the presence of oxygen and even carbon (in one case) were found. We should not exclude that superconductivity in Ti₂InN may be very sensitive towards non-stoichiometry (like in the case of oxygen content in YBa₂Cu₃O_7-d , when reduction of oxygen below 6.6-6.5 atoms per one unite cell leads to disappearance of superconductivity) or toward impurities.  A pressure of 130 bar of nitrogen was not enough to suppress the decomposition of Ti₂InN at 900 ^oC (Routes 1 and 5). The material decomposed because of In sublimation and aggregation into drops on the top of the samples (a maximum of 54 wt.% Ti₂InN was observed in the materials after 10 h heating). The sample prepared by Route 1 demonstrated the best SC behavior, but the amount of Ti₂InN was only 6.5 wt.%. Instead, 9 wt. % TiN, 14.5 wt. % In, 61 wt. % TiO₂ and 9 wt. % In₂O₃ were found. The large amount of oxygen containing phases can be explained by the fact that not all air was removed from the furnace before the high nitrogen pressure was created. In the case of Route 5, when air was removed carefully, the sample decomposed as well and contained besides 54 wt.% of Ti₂InN, 25 wt. % TiN, 20 wt.% In, and 1 wt.%TiO₂ It seems unlikely that using nitrogen instead of argon would allow to overcome this problem (i.e. that 130 bar Ar pressure can prevent In from sublimation from Ti₂InN).  All our samples contain TiN in the form of separate inclusions (with a small amount of oxygen and a very small amount of indium,). The beginning of the SC transition of all our samples was approximately 5K. The SC transition temperature of TiN was reported to be 5.3-6 K. We did not find a clear correlation between the amount of TiN and the magnetization of the materials. However, the grains of TiN phase are still a candidate for the superconducting phase in our materials. 

A detailed study of the Ti₂InN materials structures which demonstrated Tc=7.3 K would be of great interest. Especially in view of the transition temperatures reported for g-Ti₃O₅ (7.1 K) and TiO (7.4 K) films.