Aymen Yangui | Université Paris Saclay (original) (raw)
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Papers by Aymen Yangui
Scientific reports, 2015
The dynamics of the thermally induced first-order structural phase transition in a high-quality s... more The dynamics of the thermally induced first-order structural phase transition in a high-quality single crystal of the organic-inorganic perovskite (C12H25NH3)2PbI4 was investigated by optical microscopy. The propagation of the straight phase front (habit plane) during the phase transition along the cooling and heating pathways of the thermal hysteresis was observed. The thermochromic character of the transition allowed monitoring of the thermal dependence of average optical density and aided the visualization of the interface propagation. The thermal hysteresis loop is 10 K wide, and the interface velocity is constant at V ≈ 1.6 mm s(-1). The transition is accompanied with sizeable change in crystal size, with elongation of ~6% along the b axis and compression of ~ -2% along the a axis, in excellent agreement with previously reported X-ray diffraction data. The progression of the habit plane is at least 160 times faster than in spin-crossover materials, and opens new prospects for o...
The Journal of Physical Chemistry C, 2015
Journal of Luminescence, 2015
The new organic-inorganic compound (C 6 H 14 N) 3 Bi 2 I 9 has been grown by the solvent evaporat... more The new organic-inorganic compound (C 6 H 14 N) 3 Bi 2 I 9 has been grown by the solvent evaporation method. The zero-dimensional (0-D) structure for the bismuth-iodide (C 6 H 14 N) 3 Bi 2 I 9 has been determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group P1c1 and consists of a cyclohexylammonium cations and a discrete (0-D) anion built up of face-sharing bioctahedra which are interconnected by means of hydrogen bonding contacts N-H⋯I. The optimized molecular structure and vibrational spectra were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the LanL2DZ basis set. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out. Optical transmission measurements performed on thin films of (C 6 H 14 N) 3 Bi 2 I 9 revealed three absorption bands at 3.51, 2.91 and 2.46 eV. Photoluminescence measurements showed a peak at around 2.06 eV. The unaided-eye-detectable red luminescence emission comes from the excitonic transition in the Bi 2 I 9 anions.
![Research paper thumbnail of Bis[tris(propane-1,3-diamine-κ 2 N , N ′)nickel(II)] diaquabis(propane-1,3-diamine-κ 2 N , N ′)nickel(II) hexabromide dihydrate](https://attachments.academia-assets.com/47605077/thumbnails/1.jpg)
](Acta Crystallographica Section E Structure Reports Online, 2014
Key indicators: single-crystal X-ray study; T = 296 K; mean (C-C) = 0.005 Å; R factor = 0.038; wR... more Key indicators: single-crystal X-ray study; T = 296 K; mean (C-C) = 0.005 Å; R factor = 0.038; wR factor = 0.084; data-to-parameter ratio = 33.8.
![Research paper thumbnail of Evidence and detailed study of a second-order phase transition in the (C6H11NH3)2[PbI4] organic-inorganic hybrid material](https://attachments.academia-assets.com/47572425/thumbnails/1.jpg)
](The thermal properties of the organic-inorganic hybrid material (C6H11NH3)2[PbI4] are investigate... more The thermal properties of the organic-inorganic hybrid material (C6H11NH3)2[PbI4] are investigated using diffuse reflectivity, spectroscopic ellipsometry, differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. The diffuse reflectivity, performed in heating mode, clearly evidences the presence of a singularity at 336 K. This is confirmed by the temperature dependence of the spectroscopic ellipsometry spectra, which points out a second-order phase transition
at 336K with a critical exponent 0.5. Differential scanning calorimetry measurements on a polycrystalline powder of (C6H11NH3)2[PbI4] show a reversible phase transition detected at TC=336K without hysteresis. Raman spectroscopy data suggest that this transition arises from a change in the interactions between inorganic sheets ({[PbI4]2}1) and organic protonated molecules ([C6H11NH3]+). The structural analysis from power X-ray diffraction reveals an incomplete order- disorder transition of the cyclohexylammonium cation, causing a subtle contraction of the inter-plane distance. The transition results from repulsive close contacts between the organic molecules in the interlayer spacing.
Scientific reports, 2015
The dynamics of the thermally induced first-order structural phase transition in a high-quality s... more The dynamics of the thermally induced first-order structural phase transition in a high-quality single crystal of the organic-inorganic perovskite (C12H25NH3)2PbI4 was investigated by optical microscopy. The propagation of the straight phase front (habit plane) during the phase transition along the cooling and heating pathways of the thermal hysteresis was observed. The thermochromic character of the transition allowed monitoring of the thermal dependence of average optical density and aided the visualization of the interface propagation. The thermal hysteresis loop is 10 K wide, and the interface velocity is constant at V ≈ 1.6 mm s(-1). The transition is accompanied with sizeable change in crystal size, with elongation of ~6% along the b axis and compression of ~ -2% along the a axis, in excellent agreement with previously reported X-ray diffraction data. The progression of the habit plane is at least 160 times faster than in spin-crossover materials, and opens new prospects for o...
The Journal of Physical Chemistry C, 2015
Journal of Luminescence, 2015
The new organic-inorganic compound (C 6 H 14 N) 3 Bi 2 I 9 has been grown by the solvent evaporat... more The new organic-inorganic compound (C 6 H 14 N) 3 Bi 2 I 9 has been grown by the solvent evaporation method. The zero-dimensional (0-D) structure for the bismuth-iodide (C 6 H 14 N) 3 Bi 2 I 9 has been determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group P1c1 and consists of a cyclohexylammonium cations and a discrete (0-D) anion built up of face-sharing bioctahedra which are interconnected by means of hydrogen bonding contacts N-H⋯I. The optimized molecular structure and vibrational spectra were calculated by the Density Functional Theory (DFT) method using the B3LYP function with the LanL2DZ basis set. Good consistency is found between the calculated results and the experimental structure, IR, and Raman spectra. The detailed interpretation of the vibrational modes was carried out. Optical transmission measurements performed on thin films of (C 6 H 14 N) 3 Bi 2 I 9 revealed three absorption bands at 3.51, 2.91 and 2.46 eV. Photoluminescence measurements showed a peak at around 2.06 eV. The unaided-eye-detectable red luminescence emission comes from the excitonic transition in the Bi 2 I 9 anions.
Acta Crystallographica Section E Structure Reports Online, 2014
Key indicators: single-crystal X-ray study; T = 296 K; mean (C-C) = 0.005 Å; R factor = 0.038; wR... more Key indicators: single-crystal X-ray study; T = 296 K; mean (C-C) = 0.005 Å; R factor = 0.038; wR factor = 0.084; data-to-parameter ratio = 33.8.
The thermal properties of the organic-inorganic hybrid material (C6H11NH3)2[PbI4] are investigate... more The thermal properties of the organic-inorganic hybrid material (C6H11NH3)2[PbI4] are investigated using diffuse reflectivity, spectroscopic ellipsometry, differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. The diffuse reflectivity, performed in heating mode, clearly evidences the presence of a singularity at 336 K. This is confirmed by the temperature dependence of the spectroscopic ellipsometry spectra, which points out a second-order phase transition
at 336K with a critical exponent 0.5. Differential scanning calorimetry measurements on a polycrystalline powder of (C6H11NH3)2[PbI4] show a reversible phase transition detected at TC=336K without hysteresis. Raman spectroscopy data suggest that this transition arises from a change in the interactions between inorganic sheets ({[PbI4]2}1) and organic protonated molecules ([C6H11NH3]+). The structural analysis from power X-ray diffraction reveals an incomplete order- disorder transition of the cyclohexylammonium cation, causing a subtle contraction of the inter-plane distance. The transition results from repulsive close contacts between the organic molecules in the interlayer spacing.