Specific heats ofTl3AsSe3,Tl3SbS3, AgTlS, and AgTlSe between 1 and 50 K

The specific heats of ${\mathrm{Tl}}_3$As${\mathrm{Se}}_3$, ${\mathrm{Tl}}_3$Sb${\mathrm{S}}_3$, AgTlS, and AgTlSe have been measured between 1 and 50 K. The Debye temperatures are, respectively: 140, 145, 160, 140 K. Above 2.5 K an additional contribution is noticed which indicates low-lying optical modes.