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Influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals

Wunschel, Markus ; Dinnebier, Robert E. ; Carlson, Stefan ; [et al.]

International Union of Crystallography (IUCr) ; 2003

In: Acta Crystallographica Section B Structural Science Vol. 59, No. 1 ( 2003-02-01), p. 60-71

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In: Acta Crystallographica Section B Structural Science, International Union of Crystallography (IUCr), Vol. 59, No. 1 ( 2003-02-01), p. 60-71

Abstract: The crystal structures of tert -butyl-tris(trimethylsilyl)silane, Si[C(CH_3)_3]_1[Si(CH_3)_3] _3 (Bu1), and di- tert -butyl-bis(trimethylsilyl)silane, Si[C(CH_3)_3]_2[Si(CH_3)_3] _2 (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm\bar{3}m symmetry ( Z = 4) with a = 13.2645 (2) Å, V = 2333.87 (4) Å 3 for Bu1 and a = 12.9673 (1) Å, V = 2180.46 (3) Å 3 for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures T_c = 230 (5) K (Bu1) and T_c = 250 (5) K (Bu2) into monoclinic structures with space group P2_1/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) Å, \gamma = 109.477 (4)°, V = 4172.7 (8) Å 3 and Z = 8 for Bu1and a = 17.0089 (9), b = 15.3159 (8), c = 15.9325 (8) Å, \gamma = 110.343 (3)°, V = 3891.7 (5) Å 3 and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13–0.28 GPa for Bu1 and 0.20–0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder–order phase transitions.

Type of Medium: Online Resource

ISSN: 0108-7681

URL: Article

DOI: 10.1107/S0108768102021791

DOI: 10.1107/S0108768102021791/os0101sup1.cif

DOI: 10.1107/S0108768102021791/os01011sup2.hkl

DOI: 10.1107/S0108768102021791/os01012at105sup3.hkl

DOI: 10.1107/S0108768102021791/os01012at295sup4.hkl

Language: Unknown

Publisher: International Union of Crystallography (IUCr)

Publication Date: 2003

detail.hit.zdb_id: 2020841-8

SSG: 13

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Bulk modulus and non-uniform compression of Nb 3 Te 4 and In x Nb 3 Te 4 ( x 〈 1) channel compounds

Wunschel, Markus ; Dinnebier, Robert E. ; Carlson, Stefan ; [et al.]

International Union of Crystallography (IUCr) ; 2001

In: Acta Crystallographica Section B Structural Science Vol. 57, No. 5 ( 2001-10-01), p. 665-672

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In: Acta Crystallographica Section B Structural Science, International Union of Crystallography (IUCr), Vol. 57, No. 5 ( 2001-10-01), p. 665-672

Abstract: The crystal structures of Nb 3 Te 4 and In x Nb 3 Te 4 [ x = 0.539 (4)] are reported for a series of pressures between 0 and 40 GPa. Both compounds crystallize in space group P 6 3 / m with a = b = 10.671 and c = 3.6468 Å for Nb 3 Te 4 , and a = b = 10.677 and c = 3.6566 Å for In x Nb 3 Te 4 at ambient conditions. Phase transitions were not observed. High-pressure X-ray powder diffraction was measured using a diamond anvil cell and synchrotron radiation. Full Rietveld refinements provided the values of the lattice parameters and the values of the atomic coordinates at each pressure. The bulk modulus is found as K 0 = 70 (5) GPa for Nb 3 Te 4 and as K 0 = 73 (4) GPa for In x Nb 3 Te 4 . The analysis of the pressure dependences of the detailed crystal structures shows that the compression along c involves the folding up of the quasi-one-dimensional zigzag chains of Nb. The compression perpendicular to c is entirely due to the reduction of the diameter of the channels. The presence of intercalated In atoms is found to have hardly any influence on the compression behaviour up to 40 GPa.

Type of Medium: Online Resource

ISSN: 0108-7681

URL: Article

DOI: 10.1107/S0108768101011685

DOI: 10.1107/S0108768101011685/ck0007sup1.cif

DOI: 10.1107/S0108768101011685/ck0007innbtesup2.rtv

DOI: 10.1107/S0108768101011685/ck0007sup3.txt

DOI: 10.1107/S0108768101011685/ck0007sup4.txt

DOI: 10.1107/S0108768101011685/ck0007sup5.txt

DOI: 10.1107/S0108768101011685/ck0007sup6.txt

Language: Unknown

Publisher: International Union of Crystallography (IUCr)

Publication Date: 2001

detail.hit.zdb_id: 2020841-8

SSG: 13

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Structure of compounds E (SnMe 3 ) 4 ( E = Si, Ge) as seen by high-resolution X-ray powder diffraction and solid-state NMR

Dinnebier, Robert E. ; Bernatowicz, Piotr ; Helluy, Xavier ; [et al.]

International Union of Crystallography (IUCr) ; 2002

In: Acta Crystallographica Section B Structural Science Vol. 58, No. 1 ( 2002-02-01), p. 52-61

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In: Acta Crystallographica Section B Structural Science, International Union of Crystallography (IUCr), Vol. 58, No. 1 ( 2002-02-01), p. 52-61

Abstract: The compounds tetrakis(trimethylstannyl)germane, Ge(SnMe 3 ) 4 (1), and tetrakis(trimethylstannyl)silane, Si(SnMe 3 ) 4 (2), have crystal structures with the quasispherical molecules in a closed-packed stacking. At room temperature both structures have the space group P \bar 1 ( Z = 2) with a = 9.94457 (5), b = 14.52927 (8), c = 9.16021 (5) Å, α = 90.53390 (30), β = 111.73080 (30), γ = 90.0049 (4)°, and V = 1229.414 (12) Å 3 for (1) and a = 9.92009 (7), b = 14.51029 (11), c = 9.13585 (7) Å, α = 90.4769 (4), β = 111.6724 (4), γ = 89.9877 (6)°, and V = 1222.037 (16) Å 3 for (2). The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as shown by analyzing the distances between the atoms. Upon heating, both compounds undergo a first-order phase transition at temperatures T c = 348 ± 5 K, as characterized by a relative jump of the lattice parameter of ∼16%. At 353 K, both structures have the space group P \bar 1 ( Z = 4), with a = 14.2037 (2) Å, and V = 2865.52 (7) Å 3 for (1) and a = 14.1346 (2) Å, and V = 2823.90 (7) Å 3 for (2). Rietveld refinements were performed for the low-temperature phases measured at T = 295 K [ R wp = 0.0844 for (1), R wp = 0.0940 for (2)] and for the high-temperature phases measured at T = 353 K [ R wp = 0.0891 for (1), R wp = 0.0542 for (2)]. The combination of high-resolution X-ray powder diffraction measurements and variable-temperature magic-angle-spinning 13 C, 29 Si and 119 Sn NMR experiments demonstrates low crystallographic and molecular ( C 1 ) symmetries for the low-temperature phases of (1) and (2) at temperatures T 〈 348 ± 5 K and high crystallographic symmetry due to rotational disorder for the high-temperature phases at temperatures T 〉 348 ± 5 K.

Type of Medium: Online Resource

ISSN: 0108-7681

URL: Article

DOI: 10.1107/S0108768101016688

DOI: 10.1107/S0108768101016688/os0078sup1.cif

DOI: 10.1107/S0108768101016688/os0078sisnmesup2.rtv

DOI: 10.1107/S0108768101016688/os0078gesnmesup3.rtv

Language: Unknown

Publisher: International Union of Crystallography (IUCr)

Publication Date: 2002

detail.hit.zdb_id: 2020841-8

SSG: 13

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