TY - JOUR A1 - Mikat, Jürgen E. R. A1 - Franco, Olga A1 - Regenstein, Wolfgang A1 - Reck, Günter A1 - Knochenhauer, Gerald A1 - Schulz, Burkhard A1 - Orgzall, Ingo T1 - 1,3,4-oxadiazole crystals under high pressure-phase transitions and properties Y1 - 2000 ER - TY - JOUR A1 - Franco, Olga A1 - Orgzall, Ingo A1 - Regenstein, Wolfgang A1 - Schulz, Burkhard T1 - Structural and spectroscopical study of a 2,5-diphenyl-1,3,4-oxadiazole polymorph under compression N2 - The x-ray pattern and the Raman and luminescence spectra of crystalline 2,5-diphenyl-1,3,4-oxadiazole in one of its polymorphic forms (DPO II) have been investigated under pressure up to 5 GPa. The behaviour of the lattice parameters under compression was determined and it was found that the Murnaghan equation of state provides a good description of the volume-pressure relationship of DPO II. The values for the bulk modulus and its pressure derivative are K-0 = 8.6 GPa and K-0' = 7.2. The analysis of the Raman spectrum under compression clearly shows the pressure- induced shift of the Raman modes to higher frequencies. The mode Gruneisen parameters for the lattice modes were determined. Additionally, it was found that the emission spectrum of DPO II moves to lower energies and that the luminescence intensity decreases when pressure is applied Y1 - 2006 UR - http://iopscience.iop.org/0953-8984 U6 - https://doi.org/10.1088/0953-8984/18/4/029 SN - 0953-8984 ER - TY - JOUR A1 - Franco, Olga A1 - Orgzall, Ingo A1 - Reck, Günter A1 - Stockhause, Sabine A1 - Schulz, Burkhard T1 - Structure and high-pressure behavior of 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole N2 - The crystalline structures of two modifications of a compound containing the oxadiazole ring, 2,5-di-(4- aminophenyl)-1,3,4-oxadiazole (DAPO) were determined. One of these modifications contains water molecules in the crystal structure, which is observed for the first time for an oxadiazole crystal. Both crystals show an orthorhombic structure. The water free modification, DAPO L belongs to the space group Pbca (61) and has the lattice parameters: a = 13.461(5), b = 7.937(3) and c = 22.816(8) angstrom (CCDC 246608). The water containing pseudo-polymorph, DAPO 11, has the space group Cmcm (63) and the lattice parameters: a = 16.330(5), b = 12.307(2) and c = 6.9978(14) angstrom (CCDC 246609). To gain information on the inter molecular interactions within the crystals, X-ray experiments under compression at ambient temperature and under heating at vacuum conditions were performed. Neither DAPO I nor DAPO II undergo phase transitions in the ressure range up to 5 GPa, as could be concluded from X-ray and Raman experiments. X-ray and calorimetric studies indicate that DAPO II dehydrates into DAPO I under increasing temperature. Structural considerations suggest a two-stage process. The compression behavior of both substances is well described by the Murnaghan equation of state (MEOS) and the values of the bulk modulus and its pressure derivative are determined for these crystals. Additionally, in the case of DAPO I, also the thermal expansion coefficient an was measured. (c) 2005 Elsevier Ltd. All rights reserved Y1 - 2005 SN - 0022-3697 ER - TY - JOUR A1 - Orgzall, Ingo A1 - Franco, Olga A1 - Reck, Guenter A1 - Schulz, Burkhard T1 - High-pressure studies on fluorine substituted 2,5-di(phenyl)-1,3,4-oxadiazoles N2 - Results are presented from structural and high-pressure investigations on four differently but symmetrically fluorine substituted 2,5di(phenyl)-1,3,4-oxadiazoles. The substitution pattern includes the para-, meta-, or ortho- substitution and the fully fluorinated 2,5-bis(pentafluorophenyl)-1,3,4-oxadiazole. The crystal structure depends on the molecular structure and results in a different high-pressure behavior. Parameters for the Murnaghan equation of state (EOS) are determined for every compound and the anisotropic pressure response of the crystal lattice is discussed. Although the EOS parameters, bulk modulus K. and its pressure derivative K'(o) are of the same order of magnitude for all four compounds, the anisotropy of strain is noticeably different. (c) 2005 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0022-2860 ER - TY - JOUR A1 - Orgzall, Ingo A1 - Franco, Olga A1 - Schulz, Burkhard T1 - High pressure structural investigations of 2,5-di(4-pyridyl)-1,3,4-oxadiazole - importance of strain studies for the description of intermolecular interactions N2 - Results of a high pressure x-ray study of 2,5-di(4-pyridyl)-1,3,4-oxadiazole up to 2.5 GPa are presented and discussed. Parameters for the Murnaghan equation of state are derived. The bulk modulus amounts to K-0 = 4.6 +/- 0.3 GPa and its pressure derivative to K-0' = 7.4 +/- 0.6. These values are comparable to values of other diphenyl-1,3,4- oxadiazoles. The anisotropy of the compression is analysed using the strain tensor and discussed based on the anisotropy of the intermolecular interactions Y1 - 2006 UR - http://iopscience.iop.org/0953-8984 U6 - https://doi.org/10.1088/0953-8984/18/23/001 ER -