Thermal expansion of La3S4 at low temperatures

The thermal expansion of the superconductor La₃S₄ has been investigated on a single crystal by a capacitive method between 1.6 and 14 K. The relative length change shows a well pronounced second order phase transformation near 8.05 K, which is caused by the superconducting transition. From the calculated linear thermal expansion coefficient we determine the pressure coefficient of the transition temperature and of the thermodynamic critical field as well as the thermodynamic critical field itself. Furthermore we estimate the electronic, phononic and total Grüneisen parameters. These parameters have been used to discuss on the basis of the McMillan equation the reason for the increase of the transition temperature under pressure.