Second-order structural transition in the superconductor La sub(3) Co sub(4) Sn sub(13)

The quasiskutterudite superconductor La sub(3) Co sub(4) Sn sub(13) undergoes a phase transition at super(T)* = 152 K. By measuring the temperature dependence of heat capacity, electrical resistivity, and the superlattice reflection intensity using x rays, we explore the character of the phase transition at T*. Our lattice dynamic calculations found imaginary phonon frequencies around the M point when the high-temperature structure is used in the calculations, indicating that the structure is unstable at the zero-temperature limit. The combined experimental and computational results establish that T* is associated with a second-order structural transition with q= (0.5, 0.5, 0) (or the M point). Further electronic band structure calculations reveal Fermi surface sheets with low-curvature segments, which allow us to draw qualitative comparison with both Sr sub(3) Ir sub(4) Sn sub(13) and Sr sub(3) Rh sub(4) Sn sub(13) in which similar physics has been discussed recently.