Low-temperature heat capacities of yttrium, lanthanum, and lutetium sesquisulfides

The heat capacities of δ-YS1.491, α-La₂S₃, β-La₂S₃, and ε-Lu₂S₃ were measured from 1.2 to 20 K and that of δ-YS1.497 from 0.3 to 20 K. The heat capacities of the two La₂{S}₃$ samples and the ${Lu}₂S₃ sample exhibited only a T³ dependence, i.e., the electronic specific constant γ was found to be zero within ±{}0.02 mJ/g-at.K². This indicates that these materials are insulators or semiconductors. The temperature dependence of the heat capacity of the two substoichiometric δ-YSₓ samples exhibited both T and T³ dependences. The small γ values indicated that some conduction electrons were present, and that the stoichiometric δ-Y₂S₃ would be a semiconductor or insulator.