The pressure-induced structural transformation of La2S3

Abstract

As a fundamental thermodynamic parameter, pressure can cause matters to produce new phases with unique physical properties. In this paper, the pressure-induced behavior of La2S3 has been investigated in depth by in-situ high pressure synchrotron angle dispersive X-ray diffraction (ADXRD), and the pressure is up to 26 GPa. We find the conventional La2S3 which was stable at ambient pressure, was destabilized with the application of pressure and decomposed into La3S4 and LaS2 at 13.4 GPa. This is the first time that the high pressure decomposition of La2S3 has been found in the experiments. The La2S3 possesses the lowest formation enthalpy at atmospheric pressure, enthalpy change increases with the pressure increasing, leading to the decomposition of La2S3. The high pressure inhibits the ability of S atoms to accept electrons and promotes the polymerization of S atoms to form shared electron pairs, brings in the change of S–S bonding modes, and also further leads to the change of structural. The study of pressure relief experiment shows that the pressure induced decomposition in La2S3 is an irreversible phase transition. The different radial direction has the different compression effects under pressure, the initial structure decays rapidly driven by pressure. With the pressure rising, the decay rate becomes gentle. The volume expansion of La3S4 and LaS2 may be due to some defects, and the smaller the volume, the greater the bulk modulus. This work provides a strong support for the theoretical research results and is expected to provide guidance for the experiment study of the physical properties and structural characteristics of La–S system and other rare earth sulfur compounds.