Phase transitions in Lu₂Ir₃Si₅

Abstract

We report the results of our investigations on a polycrystalline sample of Lu₂Ir₃Si₅, which crystallizes in the U₂Co₃Si₅-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 150-250K 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; successive heating and/or 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 thermally cycled piece of the sample decays exponentialy with time with a decay-time constant estimated to be about 10⁴ s. The anomaly (upturn) in the resistivity and the large drop (~40%) in the susceptibility across the high-temperature transition suggest that the observed structural change is accompanied or induced by an electronic transition.