Electronic Band Structure of Cadmium Chromium Chalcogenide Spinels: CdCr2S4 and CdCr2Se4

The compounds Eu16Sb11 and Eu16Bi11 have been prepared from the elements in Ta containers by heating at 1100°C and then slowly cooled to 1000°C over 4 days.These compounds are isostructural with the Zintl-phase Ca16Sb11 and crystallize in the tetragonal space group P 21m (Z=2). The structures were determined from single-crystal X-ray data (T=143 K) for Eu16Sb11 (a=12.674 (2) ?, c=11.720 (2) ?, R1=4.04% wR2=0.84%), and Eu16Bi11 (a=12.885 (2) ?, c=11.883 (4) ?, R1=6.09%, wR2=15.24%). The Ca16Sb11 structure type can be described as pairs of face-shared square antiprisms that are joined by means of a square prism to form a columnar chain composed of Ca2+ cations and centered by Sb anions along the c axis. The columns are associated by means of Ca-Ca bonds that alternate long and short along the c axis in a ladder-like fashion. Along the a and b axes, there is an intergrowth of square prism, antiprism columns alternating with columns of facesharing hexagonal antiprisms. The structures of these Eu compounds are compared with those of Ca16Sb11. Temperature-dependent resistivity of Eu16Sb11 indicates that it is a semiconductor. Magnetization measurements show that Eu16Sb11 and Eu16Bi11 are paramagnetic. The effective moment in the paramagnetic state for Eu16Sb11 is muexp=32.2 (1) muB per formula unit (8.06 (3) muB/Eu atom) and for Eu16Bi11, muexp=33.6 (2) muB/formula unit (8.40 (6) muB/Eu atom), consistent with divalent Eu2+ cations (mueff=7.94 muB/Eu atom).