The crystal structure of the paraelectric bismuth thiochloride, BiSCl

Abstract

The crystal structure of BiSCl has been redetermined with threedimensional intensities, measured on a computer-controlled Philips PW1100 single-crystal diffractometer (628 independent reflexions). The structure does not deviate in principle from that proposed by Dönges (1950), but it shows interesting details. The cell constants, obtained by least-squares calculations from direct 3-value measurements on the diffractometer, are: a = 7.7508(16), b = 9.9920(5), c = 3.9955(5) Ä, Ζ = 4; the space group is Pnam. The positional and vibrational parameters, with anisotropic temperature factors, were refined by full-matrix, least-squares calculations to a final R = 0.036.Each Bi atom is seven-coordinated by three S atoms at distances 2.605 -2.711 Ä and four chlorine atoms at distances 2.927-3.367 Ä. The four CI atoms form a square parallel to c, while the three S atoms form an isosceles triangle perpendicular to (001), with its base parallel to c. The four CI and two of the S atoms are at the vertices of a triangular prism parallel to c and of height equal to c. The third S atom is at the apex of a pyramid whose base is one of the S 2 C1 2 faces of the triangular prism. The composite coordination polyhedron (prism-pyramid) is linked to a symmetry-equivalent polyhedron by a common S -S edge of the corresponding pyramids. This characteristic double-polyhedron system is repeated along the c axis, thus forming an infinite double chain of composition {Bi 2 S 4 Cl 8 }". The chain is further linked to each of four similar chains by a common (CI -Cl)" row parallel to c. This system of chains explains very well the needle-like growth of the crystals along c.

The crystal structure of antimony telluroiodide, SbTel

“…In view of the very large absorption coefficient (μ = 210.0 cm" 1 ) and the brittleness of the crystals, an exact absorption calculation was out of question, so the intensities of the symmetry-equivalent reflections in all quadrants were measured and averaged. This method of experimentally taking into account the effects of absorption had worked very well in the similar cases of BiSCl (Voutsas and Rentzeperis, 1980) and SbSel (Voutsas and Rentzeperis, 1982) and, as it turned out, proved very effective in the present case as well. The intensities of 1906 reflections in the range 9 = 3 0 to 9 = 31 c (range h = 0 to 13, k = ±6, / = -13 to + 9), were examined and measured.…”

“…In a similar way, each I atom is linked to two pairs of Sb atoms at distances 3.230 and 3.827 Â and occupies the apex of a pyramid, whose rectangular base is formed by the Sb atoms and is perpendicular to (010). Although, the coordination polyhedron is similar to that of the orthorhombic BiSCl (Voutsas and Rentzeperis, 1980) and SbSel (Voutsas and Rentzeperis, 1982), yet the structure of SbTel is different and constitutes a new structure type. Following the procedure outlined in the structure of BiSCl (Voutsas and Rentzeperis, 1980) the possible state of the atoms in SbTel was examined by comparing the obtained interatomic distances with the expected values from the literature.…”

“…A reliable structural model is absolutely necessary for the explanation of the interesting physical properties (optical, ferroelectric, etc,) shown by several members of the group (cf. Teng, Balkanski, Massot and Ziolkiewicz, 1974;Siapkas, 1982;Bartzokas and Siapkas, 1976; Koutsoudakis, Louizis, Bartzokas and Siapkas, 1976; Bartzokas and Siapkas, 1980;Voutsas and Rentzeperis, 1980;Voutsas and Rentzeperis, 1982).…”

The crystal structure of antimony selenide, Sb2Se3

“…In view of the very large absorption coefficient (μ = 313.1 cm -1 ) and the brittleness of the crystals an exact absorption calculation could not be carried out, so the intensities of the symmetry-equivalent reflections in all octants were measured and averaged. This method of experimentally taking into account the effects of absorption had worked very well in the similar cases of BiSCl, SbSel and BiSBr (Voutsas and Rentzeperis, 1980, 1982, 1984. The intensities of 3828 reflections in the range θ = 3 to 27° (maxima h= +12, k= ±5, / = + 12) were examined and measured.…”

The crystal structure of bismuth sulfide bromide, BiSBr

“…The present investigation is part of a systematic project undertaken to accurately determine the structures of antimony and bismuth thio and seleno Brought to you by | New York University Bobst Library Technical Service Authenticated Download Date | 8/2/15 7:10 AM halogenides (Voutsas and Rentzeperis, 1980;Voutsas and Rentzeperis. 1982).…”