Crystal structure and magnetic properties of novel La(Ce, Pr)R′PbSi2S8 (R′ = Ce, Pr, Sm, Tb, Dy, Y, Ho and Er) compounds

The formation of the La2-xR'(x) PbSi2S8 (R' = Ce, Pr, Sm, Tb, Dy, Y, Ho, Er), Ce2-xR'(x) PbSi2S8 (R' = Pr, Sm, Tb, Dy, Y, Ho, Er), and Pr2-xR'(x) PbSi2S8 (R' = Sm, Tb, Dy, Y, Ho, Er) (x = 1.5, 1.0, 0.5) solid solutions was established. The crystal structures of LaR'PbSi2S8 (R = Ce, Sm, Tb, Dy, Y, Ho, Er), CeR'PbSi2S8 (R' = Pr, Sm, Tb, Dy, Y, Ho, Er) and PrR'PbSi2S8 (R' = Sm, Tb, Dy, Y, Ho, Er) (La2PbSi2S8 structure type, space group R (3) over barc, Pearson symbol hR78) were determined by means of single crystal X-ray diffraction. Rare-earth and lead atoms are located in split positions inside bi-capped trigonal prisms made by chalcogen atoms. The Si atoms are located in tetrahedra. The crystal structure of the La2PbSi2S8 type can be derived from the Eu3As2S8 type by random substitution of the Eu atoms by the R, R', and Pb atoms at their 18e site. The magnetic properties of LaR'PbSi2S8 (R = Ce, Sm, Tb, Dy, Y, Ho, Er), CeR'PbSi2S8 (R' = Pr, Sm, Tb, Dy, Y, Ho, Er) and PrR'PbSi2S8 (R' = Sm, Tb, Dy, Y, Ho, Er) were studied in wide temperature and magnetic field strength ranges. All these materials but weakly diamagnetic LaYPbSi2S8 were characterized as Curie-Weiss paramagnets due to the magnetic moments carried on trivalent rare-earth ions. At low temperatures, each compound exhibits distinct crystalline electric field effect, while in none of them any magnetic ordering emerges down to 1.72 K.