Phase transitions in Lu$_2$Ir$_3$Si$_5$
  We report the results of our investigations on a polycrystalline sample of Lu$_2$Ir$_3$Si$_5$ which crystallizes in the U$_2$Co$_3$Si$_5$ type structure (Ibam). These investigations comprise powder X-ray diffraction, magnetic susceptibility, electrical resistivity and high temperature (120-300 K) heat capacity studies. Our results reveal that the sample undergoes a superconducting transition below 3.5 K. It also undergoes a first order phase transition between 150-250 K as revealed by an upturn in the resistivity, a diasmagnetic drop in the magnetic susceptibility and a large anomaly (20-30 J/mol K) in the specific heat data. We observe a huge thermal hysteresis of almost 45 K between the cooling and warming data across this high temperature transition in all our measurements. Low temperature X-ray diffraction measurements at 87 K reveals that the compound undergoes a structural change at the high temperature transition. Resistivity data taken in repeated cooling and warming cycles indicate that at the high temperature transition, the system goes into a highly metastable state and successive heating/cooling curves are found to lie above the previous one and the resistance keeps increasing with every thermal cycle. The room temperature resistance of a thermaly cycled piece of the sample decays exponentialy with time with a decay time constant estimated to be about 10$^4$ secs. The anomaly (upturn) in the resistivity and the large drop (almost 45%) in the susceptibility across the high temperature transition suggest that the observed structural change is accompanied or induced by an electronic transition. 
Yogesh Singh, Dilip Pal, S. Ramakrishnan, A. M. Awasthi and S.K. Malik