STUDY OF THE CROSS-SECTION YB2S3-CAS - SO LID-SOLUTIONS AND CRYSTAL-STRUCTURES OF CA3.86YB0.09S4, CA3.10YB0.60S4 AND CA2.30YB1.14S4

Study by X-ray diffraction of various mixtures of CaS and Yb2S3 after heating at 1200 degrees C, reveals the existence of continuous domains of solid solutions with successively a NaCl-type cubic unit cell (par ameter a), a cubic unit cell (parameter 2a) and a rhombohedral structu re; Some of the structures have been determined by three dimensional X -ray diffraction. Ca3.86Yb0.09S4 [a = 5.691 Angstrom, Fm3m] and Ca3.10 Yb0.60S4 [a = 5.675 Angstrom, Fm3m] have a rock salt structure. In Ca2 .30Yb1.14S4 [a = 11.246 Angstrom, <F(4)over bar 3m>], Ca and Yb are in the same octahedral (24f) sites; octahedral (4c) and (4d) positions a re occupied respectively by Ca and Yb atoms. The order of the cations in the [111] planes accounts for the superstructure.