Crystal Structure of Zinc Calcium Oxysulfide - Springer Link

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Zinc calcium oxysulfide is an intermediate product in recovery of zinc from its sulfide by carbothermal reduction in the presence of lime. A new quaternary.
Doklady Chemistry, Vol. 393, Nos. 1–3, 2003, pp. 255–258. Translated from Doklady Akademii Nauk, Vol. 393, No. 1, 2003, pp. 52–56. Original Russian Text Copyright © 2003 by Petrova, Mar’evich, Zakharov, Selivanov, Chumarev, Udoeva.

CHEMISTRY

Crystal Structure of Zinc Calcium Oxysulfide S. A. Petrova, V. P. Mar’evich, R. G. Zakharov, E. N. Selivanov, V. M. Chumarev, and L. Yu. Udoeva Presented by Academician N.A. Vatolin May 16, 2003 Received June 9, 2003

Zinc calcium oxysulfide is an intermediate product in recovery of zinc from its sulfide by carbothermal reduction in the presence of lime. A new quaternary oxysulfide was first reported in [1]. Later on, Igiehon and coworkers [2, 3] tried to investigate the products of carbothermal reduction of iron and zinc sulfides and to determine the crystal structures of ZnCaOS and FeCaOS. In these works, this phase was indexed by the similarity method to fit the hexagonal system with the unit cell parameters a = 0.648 nm and c = 0.378 nm, which were found from geometric considerations (the minimum distance between the cations). In the authors’ opinion, these distances are determined by the O–S–O sequence along the a axis and by the S–S sequence along the c axis. However, when we tried to repeat their calculations using the diffraction data in [1–3], we found a considerable discrepancy between the experimental and calculated values of interplanar spacings (∆2θ ≤ 0.4). The same is seen from the PC-PDF file no. 48–1234 [4], where the diffraction data for the isostructural (as the authors claimed) CaFeOS compound are presented. Although the unit cell parameters of the compound are available in this file, the majority of the reflections have not been indexed, and the figure of merit SS/FOM(4) was 2(0.207, 13). In this work, we obtained for the first time the pure ZnCaOS compound and determined its crystal structure. An equimolar mixture of ZnS and CaO was annealed at 1000°ë in a helium atmosphere; a CaO excess was dissolved in acetic acid. X-ray crystallographic studies of the compound synthesized were carried out using an automated DRON–UM1 diffractometer (CuKα radiation, a pyrolytic graphite monochromator in the diffraction beam). Silicon (a = 0.543106(2) nm) was used as an external standard. In addition to the main phase, the X-ray diffraction pattern of the sample (Fig. 1) contained about 3% of impurity phases (traces of the initial compounds and ZnO and CaS as byproducts).

Institute of Metallurgy, Ural Division, Russian Academy of Sciences, ul. Amundsena 101, Yekaterinburg, 620016 Russia

The ZnCaOS diffraction pattern was indexed with the TREOR90 [5] and ITO12 [6] program packages. The calculations showed that the compound can be attributed to the hexagonal system with the unit cell parameters a = 0.37547(1) nm and c = 1.14014(5) nm. The refinement of the unit cell parameters and volume (Table 1), as well the space group determination, was performed with the CELREF3 and CHECKCELL program packages [7]. In contrast to [1–3], all reflections of this phase in the diffraction pattern were indexed. The Smith–Snyder figure of merit SS/FOM(30) was 87(0.010493, 33), which was indicative of a high reliability of the structure type found and the unit cell parameters calculated. The calculated X-ray density (Dx = 3.66 g/cm3) agreed with the measured density (Dm = 3.53 g/cm3) within the experimental error. Five possible space groups were found: P31c (159), P-31c (163), P63mc (186), P-62c (190), and P63/mmc (194). With regard to the symmetry and space groups of the initial compounds, two space groups—P31c (159) and P63mc (186)—were chosen for further calculations. The crystal structure was solved using the EXPO program package [8]. The best results were obtained for space group P63mc. The zinc and oxygen atoms were found to occupy the 2(a) positions with z ≈ 0.850 and z ≈ 0.175, respectively, and the calcium and sulfur atoms to occupy the 2(b) positions with z ≈ 0.120 and z ≈ 0.430, respectively. Rietveld fullprofile analysis [9] was used to finally refine the crystal structure. The results are presented in Table 2. The experimental diffraction pattern, calculated profile, difference curve, and diffraction diagram are shown in Figs. 2a and 2b. The atoms are located in layers packed along the [001] direction in the BAABCAAC sequence (zinc or oxygen atoms occupy A layers). The structure (Fig. 3) can also be represented as a sequence of corrugated (double) Zn–S and Ca–O layers: [BA][AB][CA][AC] (the underlined layers accommodate, for example, Zn and S atoms). Three sulfur atoms and an oxygen atom surround each zinc atom, and the coordination environment of a calcium atom is an octahedron of three sulfur and three zinc atoms (Table 3).

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Table 1. Indexing the ZnCaOS* diffraction pattern H

K

L

2θobs

2θcalc

∆2θ

dobs

Irel

0 1 1 0 1 1 1 0 1 1 1 2 2 1 2 2 1 0 2 1 2 1 2 2 2 1 2 2 1 2 3 1 2 2 3 2 2 1 0 2 2 1 3 2 3

0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 0 0 0 1 0 0 0 1 1 0 1 0 1 1 0 0 0 1 0 0 1 1 0 2 0 0 1 1 1

2 0 1 4 2 3 4 6 0 2 6 0 1 4 2 3 7 8 4 6 5 8 6 1 2 9 3 7 8 4 0 10 8 6 4 9 7 10 12 0 10 12 2 9 3

15.519 27.399 28.513 31.354 31.651 36.325 42.124 47.843 48.448 51.201 56.003 56.520 57.184 58.876 59.017 62.042 63.863 65.433 66.128 70.444 71.135 72.320 77.155 78.146 79.782 81.464 82.412 84.035 85.462 86.092 90.590 91.454 91.883 96.586 99.015 100.886 103.497 104.441 108.356 110.308 111.194 115.244 119.681 121.702 122.740

15.532 27.406 28.522 31.358 31.652 36.332 42.124 47.829 48.449 51.187 56.005 56.561 57.185 58.854 59.033 62.038 63.868 65.435 66.110 70.449 71.166 72.332 77.150 78.158 79.757 81.472 82.404 84.046 85.468 86.085 90.580 91.441 91.903 96.564 98.986 100.860 103.473 104.455 108.337 110.294 111.215 115.267 119.709 121.676 122.768

–0.013 –0.007 –0.009 –0.004 –0.001 –0.007 +0.001 +0.014 –0.001 +0.014 –0.003 –0.040 –0.002 +0.022 –0.017 +0.005 –0.005 –0.001 +0.018 –0.006 –0.031 –0.012 +0.005 –0.012 +0.025 –0.008 +0.008 –0.011 –0.005 +0.007 +0.010 +0.013 –0.020 +0.023 +0.029 +0.026 +0.024 –0.014 +0.020 +0.014 –0.020 –0.023 –0.028 +0.026 –0.027

5.7053 3.2525 3.1280 2.8507 2.8246 2.4712 2.1434 1.8997 1.8774 1.7827 1.6407 1.6269 1.6096 1.5673 1.5639 1.4947 1.4564 1.4252 1.4119 1.3356 1.3243 1.3055 1.2353 1.2221 1.2011 1.1805 1.1693 1.1508 1.1352 1.1285 1.0838 1.0758 1.0719 1.0318 1.0129 0.9991 0.9809 0.9746 0.9500 0.9386 0.9336 0.9121 0.8909 0.8820 0.8776

22 25 35 51 100 54 18 2 41 4 35 3 3 19 19 5 4 1 3 1