Структурний тип La2PbSi2S8

Abstract

The determination of the crystal structure of the compounds La(Ce, Pr, Nd)2PbSi2S8, La(Ce, Pr, Nd)2PbSi2Se8 and Ce2PbGe2S8 was performed by X-ray single crystal method, and of the compounds Sm(Gd, Tb, Dy, Y, Ho, Er)2PbSi2S8, Sm(Gd)2PbSi2Se8, La(Pr)2PbGe2S8 and La2PbGe2Se8 by X-ray powder method. All these phases crystallize in the hexagonal unit cell of the La2PbSi2S8 type (space group R3c , Pearson symbol hR78) in which rare-earth and lead atoms are statistically distributed and center bi capped trigonal prisms of chalcogen atoms. The performed investigations determined the unit cell parameters of twenty one quaternary compounds: a = 0.9052 nm, c = 2.6964 nm, V = 1.9135 nm3 (La2PbSi2S8); a = 0.9003 nm, c = 2.6765 nm, V = 1.8787 nm3 (Ce2PbSi2S8); a = 0.8974 nm, c = 2.6640 nm, V = 1.8581 nm3 (Pr2PbSi2S8); a = 0.8942 nm, c = 2.6492 nm, V = 1.8348 nm3 (Nd2PbSi2S8); a = 0.8885 nm, c = 2.6283 nm, V = 1.7970 nm3 (Sm2PbSi2S8); a = 0.8863 nm, c = 2.6185 nm, V = 1.7815 nm3 (Gd2PbSi2S8); a = 0.8860 nm, c = 2.6118 nm, V = 1.7798 nm3 (Tb2PbSi2S8); a = 0.8842 nm, c = 2.6003 nm, V = 1.7607 nm3 (Dy2PbSi2S8); a = 0.8843 nm, c = 2.5975 nm, V = 1.7592 nm3 (Y2PbSi2S8); a = 0.8842 nm, c = 2.5963 nm, V = 1.7582 nm3 (Ho2PbSi2S8); a = 0.8830 nm, c = 2.5840 nm, V = 1.7448 nm3 (Er2PbSi2S8); a = 0.9398 nm, c = 2.8089 nm, V = 2.1487 nm3 (La2PbSi2Se8); a = 0.9351 nm, c = 2.7908 nm, V = 2.1138 nm3 (Ce2PbSi2Se8); a = 0.9326 nm, c = 2.7779 nm, V = 2.0925 nm3 (Pr2PbSi2Se8); a = 0.9299 nm, c = 2.7670 nm, V = 2.0725 nm3 (Nd2PbSi2Se8); a = 0.9262 nm, c = 2.7487 nm, V = 2.0421 nm3 (Sm2PbSi2Se8); a = 0.9232 nm, c = 2.7329 nm, V = 2.0172 nm3 (Gd2PbSi2Se8); a = 0.9061 nm, c = 2.7187 nm, V = 1.9331 nm3 (La2PbGe2S8); a = 0.9018 nm, c = 2.6980 nm, V = 1.9003 nm3 (Ce2PbGe2S8); a = 0.8984 nm, c = 2.6867 nm, V = 1.8780 nm3 (Pr2PbGe2S8); a = 0.9398 nm, c = 2.8273 nm, V = 2.1626 nm3 (La2PbGe2Se8). Keywords: crystal structure; X-ray powder method; rare-earth chalcogenides.