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The powder data for p-chloroiodobenzene and p-bromochlorobenzene/p-chloroiodobenzene mixed crystals [pBCB]_x[pCIB]_{1 - x} at 293 K are reported; their stability at 293 K is given. The cell dimensions have been refined by least squares from accurate powder diffractometer data recorded at T = 293 (1) K (quartz as internal standard). Vertical diffractometer, graphite monochromator, Cu K₁-Cu K₂ correction so that = 1.54056 Å. They are all isomorphous, monoclinic, P2₁/a with Z = 2. a = 15.818(4), b = 5.912(2), c = 4.214(2) Å, = 113.61(1)°, V = 361.1 Å³, D_x = 2.193 Mg m^-3 for pCIB; JCPDS No. 37-2000. a = 15.210(5), b = 5.860(3), c = 4.091(2) Å, = 112.64(2)°, V = 336.5 Å³, D_x = 1.936 Mg m^-3 for [pBCB]_0.90[pCIB]_0.10; JCPDS No. 37-1989. a = 15.287(6), b = 5.870(3), c = 4.111(2) Å, = 112.78(2)°, V = 340.1 Å³, D_x = 1.961 Mg m^-3 for [pBCB]_0.80[pCIB]_0.20; JCPDS No. 37-1990. a = 15.360(5), b = 5.880(2), c = 4.126(1) Å, = 112.87(2)°, V = 343.3 Å³, D_x = 1.988 Mg m^-3 for [pBCB]_0.70[pCIB]_0.30; JCPDS No. 37-1991. a = 15.424(5), b = 5.889(3), c = 4.137(2) Å, = 112.99(2)°, V = 346.0 Å³, D_x = 2.018 Mg m^-3 for [pBCB]_0.60[pCIB]_0.40; JCPDS No. 37-1992. a = 15.493(4), b = 5.896(2), c = 4.155(2) Å, = 113.09(2)°, V= 349.1 Å³, D_x = 2.045 Mg m^-3 for [pBCB]_0.50[pCIB]_0.50; JCPDS No. 37-1993. a = 15.566(5), b = 5.901(3), c = 4.168(2) Å, = 113.20(2)°, V = 351.9 Å³, D_x = 2.073 Mg m^-3 for [pBCB]_0.40[pCIB]_0.60; JCPDS No. 37-1994. a = 15.623(5), b = 5.904(3), c = 4.178(3) Å, = 113.26(2), V = 354.0 Å³, D_x = 2.105 Mg m^-3 for [pBCB]_0.30[pCIB]_0.70; JCPDS No. 37-1995. a = 15.691(4), b = 5.913(3), c = 4.195(2)Å, = 113.43(2)°, V = 357.1 Å³, D_x = 2.130 Mg m^-3 for [pBCB]_0.20[pCIB]_0.80; JCPDS No. 37-1996. a = 15.759(4), b = 5.906(2), c = 4.204(2) Å, = 113.55(2)°, V = 358.7 Å³, D_x = 2.164 Mg m^-3 for [pBCB]_0.10[pCIB]_0.90; JCPDS No. 37-1999.

The variations of the tensor of compositional deformation as a function of composition are determined for the ten series of mixed crystals corresponding to the ten binary systems formed by p-dichlorobenzene, p-bromochlorobenzene, p-dibromobenzene, p-chloroiodobenzene and p-bromoiodobenzene.

The powder data for p-bromochlorobenzene/p-dibromobenzene mixed crystals [pBCB]_x[pDBB]_{1 - x} at 293 K are reported; their thermal stability at 293 K is given. Vertical diffractometer, graphite monochromator, Cu K, = 1.54056 Å. They are all isomorphous, monoclinic, P2₁/a with Z = 2. a = 15.176(6), b = 5.847(3), c = 4.078(2) Å, = 112.57(3)°, V = 334.2 Å³, D_x = 1.947 Mg m^-3 for [pBCB]_0.90[pDBB]_0.10; JCPDS No. 36-1975. a = 15.222 (7), b = 5.847 (3), c = 4.083(2) Å, = 112.60(3)°, V = 335.5 Å³, D_x = 1.984 Mg m^-3 for [pBCB]_0.80[pDBB]_0.20; JCPDS No. 36-1974. a = 15.260(5), b = 5.839(2), c = 4.084(2) Å, = 112.57(1)°, V = 336.1 Å³, D_x = 2.024 Mg m^-3 for [pBCB]_0.70[pDBB]_0.30; JCPDS No. 36-1973. a = 15.298(4), b = 5.845(3), c = 4.091(2) Å, = 112.60(2), V = 337.7 Å³, D_x = 2.058 Mg m^-3 for [pBCB]_0.60[pDBB]_0.40; JCPDS No. 36-1972. a = 15.340(4), b = 5.844(2), c = 4.092(2) Å, = 112.60(2)°, V = 338.7 Å³, D_x = 2.096 Mg m^-3 for [pBCB]_0.50[pDBB]_0.50; JCPDS No. 36-1971. a = 15.370(5), b = 5.843(2), c = 4.097(2) Å, = 112.62(2)°, V = 339.6 Å³, D_x = 2.134 Mg  m^-3 for [pBCB]_0.40[pDBB]_0.60; JCPDS No. 36-1970. a = 15.404(6), b = 5.840(2), c = 4.100(2) Å, = 112.67(2)°, V = 340.4 Å³, D_x = 2.172 Mg m^-3 for [pBCB]_0.30[pDBB]_0.70; JCPDS No. 36-1969. a = 15.437(5), b = 5.842(2), c = 4.103(2) Å, = 112.66(2)°, V = 341.4 Å³, D_x = 2.209 Mg m^-3 for [pBCB]_0.20[pDBB]_0.80; JCPDS No. 36-1968. a = 15.468(4), b = 5.838(2), c = 4.104(2) Å, = 112.70(2)°, V = 341.9 Å³, D_x = 2.249 Mg m^-3 for [pBCB]_0.10[pDBB]_0.90; JCPDS No. 36-1967.

The -phase structure of the title compound, C₆H₄Cl₂, has been accurately redetermined at room temperature. Comparison with 100 K data shows that all different shortest intermolecular contacts (ClCl, ClC, ClH, CC, CH, HH) undergo thermal expansion. A three-centred hydrogen-bonding geometry is considered for some ClH contacts.

Heterojunctions GaAs-Al_xGa_1-xAs involved in the elaboration of IR laser diodes have been studied. The difference in lattice parameter between the GaAs substrate and the aluminum-substituted epitaxic layer Al_xGa_1-xAs has been measured accurately on a double-crystal spectrometer for a series of compositions. These data coupled with radius of curvature determination have permitted calculation of the stress in the layer and the bulk lattice parameter of Al_xGa_1-xAs. characterization of the defects introduced during the liquid-phase epitaxy has been performed by X-ray topography.

The powder data for p-bromochlorobenzene(pBCB) and p-dichlorobenzene/p-bromochlorobenzene mixed crystals [pDCB]_x[pBCB]_{1 - x} at 293 K are reported; their thermal stability at 293 K is given. Vertical diffractomer, graphite monochromator, Cu K, = 1.5405 Å. They are all isomorphous, monoclinic, P2₁/a with Z = 2. a = 15.134(4), b = 5.843(2), c = 4.073(1) Å, = 112.53(1)°, V = 332.7 Å³, D_x = 1.911 Mg m^-3 for pBCB. a = 14.890(5), b = 5.848(5), c = 4.046(2) Å, = 112.53(2)°, V = 325.4 ų, D_x = 1.636 Mg m^-3 for [pDCB]_0.70[pBCB]_0.30. a = 15.004(6), b = 5.840(3), c = 4.059(2) Å, = 112.48(2)°, V = 328.6 Å³, D_x = 1.755 Mg m^-3 for [pDCB]_0.40[pBCB]_0.60. a = 15.101(4), b = 5.844(2), c = 4.066(2) Å, = 112.51(2)°, V = 331.5 Å³, D_x = 1.873 Mg m^-3 for [pDCB]_{0. 10}[pBCB]_0.90. The JCPDS Nos. are: 36-1995 for pBCB; 36-1994 for [pDCB]_0.70[PBCB]_0.30; 36-1993 for [pDCB]_0.40[pBCB]_0.60; 36-1992 for [pDCB]_0.10[pBCB]_0.90. Data for [pDCB]_0.90[pBCB]_0.10, [pDCB]_0.80 [pBCB]_0.20, [pDCB]_0.60 [pBCB]_0.40, [pDCB]_0.50[pBCB]_0.50, [pDCB]_0.30[pBCB]_0.70 and [pDCB]_0.20[pBCB]_0.80 have also been measured and are available from the authors or as part of the Supplementary Publication.

The data given in the Abstract published in J. AppI. Cryst. (1985), 18, 542 are in error. The correct data are given below: