The crystalline polysiloxane (-&SiO-)n, where R = n-propyl, has been characterized through high-resolution X-ray diffraction patterns of the polycrystalline material and selected-area electronbeam diffraction patterns of single crystals. The smallest unit cell consistent with the diffraction data is tetragonal, with dimensions a = 9.52 0.01 A and c = 9.40 * 0.05 A. The probable space group is P4, (or P4,).
In a recent publi ('ation Semiletov & Man (1959) have rel)orte(I on the crystal structures of T1SbS., an(I TIBiSe.,. These were found to be of the disordered NaCI type an(l it was surmised in their paper that ('ertain other t hMlium compounds might also have this structure. However, there exist ordered stru('tures which are closely relate(1 t() the (lisordercd NaCl type. (feller & ~,Verniek (195!}) })ave foun(t that for AgBiSe., and AgFIiS~ there is a high temi)erature phase of the disordered NaC1 tyi)e, while at room temperature a hexagonal phase exists. At interme(tiate temperatures there is a rhombohe(tral structure formed by ordering of the cations in layers perpen(lieular to one of the cubic [111] (tireetions. VVe have synthesized and examined two of the e()mt)ounds me.ntioned 1)y Semiletov & Man, TISbTe., and T1BiTe.,. These comt)ounds have been found t() be isostructural with the intermcdiate phases of AgBiSe., and AgBiS.,.Specimens of TISbTe a an(t TIBiTe., were pret)are(l directly from the elements in evacuated fused silica ampules. The materials were heated to 600 °C., mixed and then cooled at a rate of about 10 ° rain. -~. By differential thermal analysis TISbTe., was found to have a melting temperature of 480 ~(?. and TIBiT% of 535 °(?. In neither ease were thermal effects observed below the melting temperatures. X-ray pow(ter patterns of both materials wer(' in(lex(,d on tim basis of a primitive rhombohe(h'al cell and the erystallogra|)hie data referre(l to this lmit cell are given in Table 1. Long ext)osure oscillation photographs of a small crystal separate(t from a Bri(tgman grown ingot of TISbTez, reveale(t no additional reflection which wouhl have required a larger unit cell. In the case of T1BiTe 2 suitable single crystals were not found, and the sl)a('ogroup assignment is consequently less (tefinitive.The atoms occupy the following special positions of the, space group R-3m: The Te free parameter x was adjusted to give the best.agreement between calculated an(t observe(t intensities, as measure(1 on a Noreleo diffraetometer using t)ow(lere(l samples, and this was found with x =0.243 for TISbTe., Acta Cryst. (1961). 14, 328A new phase in the zinc-zirconium system. An intermetallie compound Zn.~Zr:~ has been isolated by preeii)itation from a solution of zinc and zirconium in molten magnesium. It is not. mentioned in a recent com-1)rehensive s*,u(ty of the Zn-Zr system (Chiotti & Kilp, 1959) nor in the earlier literature (Hansen, 1958; Pearson, 1958).A representative sample of the new phase, consisting of those crystals retained on 100-mesh screening, contained 68.0o( / ) Zr by weight (calculated, 67.~o/~,/o/ and showe(t a density of 6"60 +_0"04 g.cm. The density, calculated on the basis of 4 Zn.,Zr a in each cell, is 6.62 g.cm. -a. The sole criterion observed for the non-extinction of reflections is /c+l even for Okl, which allows the three space groups t'42nm, 1'7~n2, and 1"4.,~mum.Powder data recorded with a GE camera of diameter 143.2 ram., using Cu Kx radiation, are listed in Table 1.
Nonstoichiometric clathrate compounds of ethylene oxide and water form cubic phases of composition xC2H4O·46H2O, where the theoretical maximum x is 8. Through x-ray diffraction experiments, thermal expansion relations were established for several specific compositions (x = 1.08, 2.32, 3.72, 6.75) over the temperature range from −140° to −20°C. It was found that in each case, the relative thermal expansion of the clathrate was greater than that of normal ice over matching ranges. At any given temperature in the range studied, a sharp break was observed in the composition expansion curve at about x = 3, for which a reasonable explanation has been provided.
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