The kinetic studies of the solvent-promoted aggregation of a steroid-porphyrin derivative

The study of the aggregation of a steroid-functionalised porphyrin derivative shows the formation of chiral suprastuctures. Kinetic studies indicate that the mechanism of the aggregation strongly depends on both the nature of the media and on the concentration of the tetrapyrrolic macrocycle

Design and studies of novel polyoxysterol-based porphyrin conjugates

New types of steroid-porphyrin conjugates derived from 20-hydroxyecdysone (20E) and 24-epibrassinolide (EBl) were synthesized. An exceptional regioselectivity in the reaction of both steroids with porphyrin boronic acids was found to give side-chain-conjugated boronic esters as sole products. UV–Vis-, fluorescence and NMR spectroscopy yielded similar data for all the studied compounds confirming the solvent driven supramolecular assembly with formation of J-aggregates. CD measurements of water diluted solutions showed a clear difference between 20E and EBl conjugates. The latter showed a strong supramolecular chirality, whereas 20E J-aggregates did not

Anomalous Raman Modes in Tellurides

Two broad bands are usually found in the Raman spectrum of many Te-based chalcogenides, which include binary compounds, like ZnTe, CdTe, HgTe, GaTe, GeTe, SnTe, PbTe, GeTe2, As2Te3, Sb2Te3, Bi2Te3, NiTe2, IrTe2, TiTe2, as well as ternary compounds, like GaGeTe, SnSb2Te4, SnBi2Te4, and GeSb2Te5. Many different explanations have been proposed in the literature for the origin of these two anomalous broad bands in tellurides, usually located between 119 and 145 cm-1. They have been attributed to the own sample, to oxidation, to the folding of Brillouin-edge modes onto the zone center, to the existence of a double resonance, like that of graphene, or to the formation of Te precipitates. In this paper, we provide arguments to demonstrate that such bands correspond to clusters or precipitates of trigonal Te in form of nanosize or microsize grains or layers that are segregated either inside or at the surface of the samples. Several mechanisms for Te segregation are discussed and sample heating caused by excessive laser power during Raman scattering measurements is emphasized. Finally, we show that anomalous Raman modes related to Se precipitates also occur in selenides, thus providing a general vision for a better characterization of selenides and tellurides by means of Raman scattering measurements and for a better understanding of chalcogenides in general.Comment: 45 pages, 8 figure

Lattice dynamics of Sb2Te3 at high pressures

We report an experimental and theoretical lattice dynamics study of antimony telluride (Sb 2Te 3) up to 26 GPa together with a theoretical study of its structural stability under pressure. Raman-active modes of the low-pressure rhombohedral (R-3m) phase were observed up to 7.7 GPa. Changes of the frequencies and linewidths were observed around 3.5 GPa where an electronic topological transition was previously found. Raman-mode changes evidence phase transitions at 7.7, 14.5, and 25GPa. The frequencies and pressure coefficients of the new phases above 7.7 and 14.5 GPa agree with those calculated for the monoclinic C2/m and C2/c structures recently observed at high pressures in Bi 2Te 3 and also for the C2/m phase in the case of Bi 2Se 3 and Sb 2Te 3. Above 25 GPa no Raman-active modes are observed in Sb 2Te 3, similarly to the case of Bi 2Te 3 and Bi 2Se 3. Therefore, it is possible that the structure of Sb 2Te 3 above 25 GPa is the same disordered bcc phase already found in Bi 2Te 3 by x-ray diffraction studies. Upon pressure release, Sb 2Te 3 reverts back to the original rhombohedral phase after considerable hysteresis. Raman- and IR-mode symmetries, frequencies, and pressure coefficients in the different phases are reported and discussed. © 2011 American Physical Society.This work has been done under financial support from Spanish MICINN under Project Nos. MAT2010-21270-C04-03/04 and CSD-2007-00045 and supported by the Ministry of Education, Youth and Sports of the Czech Republic (MSM 0021627501). E. P.-G. acknowledges the financial support of the Spanish MEC under a FPI fellowship. Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster.Gomis Hilario, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.; Rodríguez-Hernández, P.; Pérez-González, E.; Muñoz, A.; Kucek, V.... (2011). 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Journal of Applied Physics, 102(6), 064503. doi:10.1063/1.2778737Kim, M. S., Cho, S. H., Hong, S. K., Roh, J. S., & Choi, D. J. (2008). Crystallization characteristics of nitrogen-doped Sb2Te3 films for PRAM application. Ceramics International, 34(4), 1043-1046. doi:10.1016/j.ceramint.2007.09.078Anderson, T. L., & Krause, H. B. (1974). Refinement of the Sb2Te3 and Sb2Te2Se structures and their relationship to nonstoichiometric Sb2Te3−y Se y compounds. Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 30(5), 1307-1310. doi:10.1107/s0567740874004729Zhang, H., Liu, C.-X., Qi, X.-L., Dai, X., Fang, Z., & Zhang, S.-C. (2009). Topological insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with a single Dirac cone on the surface. Nature Physics, 5(6), 438-442. doi:10.1038/nphys1270Hasan, M. Z., & Kane, C. L. (2010). Colloquium: Topological insulators. Reviews of Modern Physics, 82(4), 3045-3067. doi:10.1103/revmodphys.82.3045Moore, J. E. (2010). 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V., Sharp, J., & Badding, J. V. (2001). Large Improvement in Thermoelectric Properties in Pressure-Tuned p-Type Sb1.5Bi0.5Te3. Chemistry of Materials, 13(6), 2068-2071. doi:10.1021/cm000888qChandra Shekar, N. V., Polvani, D. A., Meng, J. F., & Badding, J. V. (2005). Improved thermoelectric properties due to electronic topological transition under high pressure. Physica B: Condensed Matter, 358(1-4), 14-18. doi:10.1016/j.physb.2004.12.020Ovsyannikov, S. V., Shchennikov, V. V., Vorontsov, G. V., Manakov, A. Y., Likhacheva, A. Y., & Kulbachinskii, V. A. (2008). Giant improvement of thermoelectric power factor of Bi2Te3 under pressure. Journal of Applied Physics, 104(5), 053713. doi:10.1063/1.2973201Ovsyannikov, S. V., & Shchennikov, V. V. (2010). High-Pressure Routes in the Thermoelectricity or How One Can Improve a Performance of Thermoelectrics†. Chemistry of Materials, 22(3), 635-647. doi:10.1021/cm902000xLi, C., Ruoff, A. L., & Spencer, C. W. (1961). Effect of Pressure on the Energy Gap of Bi2Te3. Journal of Applied Physics, 32(9), 1733-1735. doi:10.1063/1.1728426Khvostantsev, L. G., Orlov, A. I., Abrikosov, N. K., & Ivanova, L. D. (1980). Thermoelectric properties and phase transition in Sb2Te3 under hydrostatic pressure up to 9 GPa. Physica Status Solidi (a), 58(1), 37-40. doi:10.1002/pssa.2210580103Sakai, N., Kajiwara, T., Takemura, K., Minomura, S., & Fujii, Y. (1981). Pressure-induced phase transition in Sb2Te3. Solid State Communications, 40(12), 1045-1047. doi:10.1016/0038-1098(81)90248-9Khvostantsev, L. G., Orlov, A. I., Abrikosov, N. K., & Ivanova, L. D. (1985). Kinetic Properties and Phase Transitions in Sb2Te3 under Hydrostatic Pressure up to 9 GPa. physica status solidi (a), 89(1), 301-309. doi:10.1002/pssa.2210890132Thonhauser, T., Scheidemantel, T. J., Sofo, J. O., Badding, J. V., & Mahan, G. D. (2003). Thermoelectric properties ofSb2Te3under pressure and uniaxial stress. Physical Review B, 68(8). doi:10.1103/physrevb.68.085201Thonhauser, T. (2004). Influence of negative pressure on thermoelectric properties of Sb2Te3. Solid State Communications, 129(4), 249-253. doi:10.1016/j.ssc.2003.10.006Einaga, M., Tanabe, Y., Nakayama, A., Ohmura, A., Ishikawa, F., & Yamada, Y. (2010). New superconducting phase of Bi2Te3under pressure above 11 GPa. Journal of Physics: Conference Series, 215, 012036. doi:10.1088/1742-6596/215/1/012036Zhang, J. L., Zhang, S. J., Weng, H. M., Zhang, W., Yang, L. X., Liu, Q. Q., … Jin, C. Q. (2010). Pressure-induced superconductivity in topological parent compound Bi2Te3. Proceedings of the National Academy of Sciences, 108(1), 24-28. doi:10.1073/pnas.1014085108Jacobsen, M. K., Kumar, R. S., Cornelius, A. L., Sinogeiken, S. V., Nico, M. F., Elert, M., … Nguyen, J. (2008). 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Semiconductors, 31(3), 276-278. doi:10.1134/1.1187126Polian, A., Gauthier, M., Souza, S. M., Trichês, D. M., Cardoso de Lima, J., & Grandi, T. A. (2011). Two-dimensional pressure-induced electronic topological transition in Bi2Te3. Physical Review B, 83(11). doi:10.1103/physrevb.83.113106Vilaplana, R., Santamaría-Pérez, D., Gomis, O., Manjón, F. J., González, J., Segura, A., … Kucek, V. (2011). Structural and vibrational study of Bi2Se3under high pressure. Physical Review B, 84(18). doi:10.1103/physrevb.84.184110Richter, W., & Becker, C. R. (1977). A Raman and far-infrared investigation of phonons in the rhombohedral V2–VI3 compounds Bi2Te3, Bi2Se3, Sb2Te3 and Bi2(Te1−xSex)3 (0 <x < 1), (Bi1−ySby)2Te3 (0 <y < 1). Physica Status Solidi (b), 84(2), 619-628. doi:10.1002/pssb.2220840226Sosso, G. C., Caravati, S., & Bernasconi, M. (2009). Vibrational properties of crystalline Sb2Te3from first principles. Journal of Physics: Condensed Matter, 21(9), 095410. doi:10.1088/0953-8984/21/9/095410Dagens, L. (1978). Phonon anomaly near a Fermi surface topological transition. Journal of Physics F: Metal Physics, 8(10), 2093-2113. doi:10.1088/0305-4608/8/10/010Dagens, L., & Lopez-Rios, C. (1979). Thermodynamic properties of a metal near a Fermi surface topological transition: the anomalous electron-phonon interaction contribution. Journal of Physics F: Metal Physics, 9(11), 2195-2216. doi:10.1088/0305-4608/9/11/011Goncharov, A. ., & Struzhkin, V. . (2003). Pressure dependence of the Raman spectrum, lattice parameters and superconducting critical temperature of MgB2: evidence for pressure-driven phonon-assisted electronic topological transition. Physica C: Superconductivity, 385(1-2), 117-130. doi:10.1016/s0921-4534(02)02311-0Antonangeli, D., Farber, D. L., Said, A. H., Benedetti, L. R., Aracne, C. M., Landa, A., … Klepeis, J. E. (2010). Shear softening in tantalum at megabar pressures. Physical Review B, 82(13). doi:10.1103/physrevb.82.132101Santamaría-Pérez, D., Vegas, A., Muehle, C., & Jansen, M. (2011). Structural behaviour of alkaline sulfides under compression: High-pressure experimental study on Cs2S. The Journal of Chemical Physics, 135(5), 054511. doi:10.1063/1.3617236Vilaplana, R., Gomis, O., Manjón, F. J., Segura, A., Pérez-González, E., Rodríguez-Hernández, P., … Kucek, V. (2011). High-pressure vibrational and optical study of Bi2Te3. Physical Review B, 84(10). doi:10.1103/physrevb.84.104112Larson, P. (2006). Effects of uniaxial and hydrostatic pressure on the valence band maximum inSb2Te3: An electronic structure study. Physical Review B, 74(20). doi:10.1103/physrevb.74.205113Lošťák, P., Beneš, L., Civiš, S., & Süssmann, H. (1990). Preparation and some physical properties of Bi2−xInxSe3 single crystals. Journal of Materials Science, 25(1), 277-282. doi:10.1007/bf00544220Horák, J., Quayle, P. C., Dyck, J. S., Drašar, Č., Lošt’ák, P., & Uher, C. (2008). Defect structure of Sb2−xCrxTe3 single crystals. Journal of Applied Physics, 103(1), 013516. doi:10.1063/1.2826940Piermarini, G. J., Block, S., & Barnett, J. D. (1973). Hydrostatic limits in liquids and solids to 100 kbar. Journal of Applied Physics, 44(12), 5377-5382. doi:10.1063/1.1662159Errandonea, D., Meng, Y., Somayazulu, M., & Häusermann, D. (2005). Pressure-induced transition in titanium metal: a systematic study of the effects of uniaxial stress. Physica B: Condensed Matter, 355(1-4), 116-125. doi:10.1016/j.physb.2004.10.030Syassen, K. (2008). Ruby under pressure. High Pressure Research, 28(2), 75-126. doi:10.1080/08957950802235640Hohenberg, P., & Kohn, W. (1964). Inhomogeneous Electron Gas. Physical Review, 136(3B), B864-B871. doi:10.1103/physrev.136.b864Kresse, G., & Hafner, J. (1993). Ab initiomolecular dynamics for liquid metals. Physical Review B, 47(1), 558-561. doi:10.1103/physrevb.47.558Kresse, G., & Hafner, J. (1994). Ab initiomolecular-dynamics simulation of the liquid-metal–amorphous-semiconductor transition in germanium. Physical Review B, 49(20), 14251-14269. doi:10.1103/physrevb.49.14251Kresse, G., & Furthmüller, J. (1996). Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Computational Materials Science, 6(1), 15-50. doi:10.1016/0927-0256(96)00008-0Kresse, G., & Furthmüller, J. (1996). Efficient iterative schemes forab initiototal-energy calculations using a plane-wave basis set. Physical Review B, 54(16), 11169-11186. doi:10.1103/physrevb.54.11169Blöchl, P. E. (1994). Projector augmented-wave method. Physical Review B, 50(24), 17953-17979. doi:10.1103/physrevb.50.17953Kresse, G., & Joubert, D. (1999). From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B, 59(3), 1758-1775. doi:10.1103/physrevb.59.1758Perdew, J. P., Ruzsinszky, A., Csonka, G. I., Vydrov, O. A., Scuseria, G. E., Constantin, L. A., … Burke, K. (2008). Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Physical Review Letters, 100(13). doi:10.1103/physrevlett.100.136406Mujica, A., Rubio, A., Muñoz, A., & Needs, R. J. (2003). High-pressure phases of group-IV, III–V, and II–VI compounds. Reviews of Modern Physics, 75(3), 863-912. doi:10.1103/revmodphys.75.863Blanco, M. A., Francisco, E., & Luaña, V. (2004). GIBBS: isothermal-isobaric thermodynamics of solids from energy curves using a quasi-harmonic Debye model. Computer Physics Communications, 158(1), 57-72. doi:10.1016/j.comphy.2003.12.001Cardona, M. (2004). Phonon widths versus pressure. High Pressure Research, 24(1), 17-23. doi:10.1080/08957950310001635819Cardona, M. (2004). Effects of pressure on the phonon–phonon and electron–phonon interactions in semiconductors. physica status solidi (b), 241(14), 3128-3137. doi:10.1002/pssb.200405202Ulrich, C., Mroginski, M. A., Goñi, A. R., Cantarero, A., Schwarz, U., Muñoz, V., & Syassen, K. (1996). Vibrational Properties of InSe under Pressure: Experiment and Theory. physica status solidi (b), 198(1), 121-127. doi:10.1002/pssb.2221980117Kulibekov, A. M., Olijnyk, H. P., Jephcoat, A. P., Salaeva, Z. Y., Onari, S., & Allakhverdiev, K. R. (2003). Raman scattering under pressure and the phase transition in ɛ-GaSe. physica status solidi (b), 235(2), 517-520. doi:10.1002/pssb.200301613Cheng, W., & Ren, S.-F. (2011). Phonons of single quintuple Bi2Te3and Bi2Se3films and bulk materials. Physical Review B, 83(9). doi:10.1103/physrevb.83.094301Buga, S. G., Serebryanaya, N. R., Dubitskiy, G. A., Semenova, E. E., Aksenenkov, V. V., & Blank, V. D. (2011). Structure and electrical properties of Sb2Te3and Bi0.4Sb1.6Te3metastable phases obtained by HPHT treatment. High Pressure Research, 31(1), 86-90. doi:10.1080/08957959.2010.52342

Spectroscopic, Morphological and Mechanistic Investigation of the Solvent.Promoted Aggregation of Porphyrins Modified in meso-positions by Glucosylated steroids

Solvent-driven aggregation of a series of porphyrin derivatives was studied by UV/Vis and circular dichroism spectroscopy. The porphyrins are characterised by the presence in the meso positions of steroidal moieties further conjugated with glucosyl groups. The presence of these groups makes the investigated macrocycles amphiphilic and soluble in aqueous solvent, namely, dimethyl acetamide/ water. Aggregation of the macrocycles is triggered by a change in bulk solvent composition leading to formation of large architectures that express supramolecular chirality, steered by the presence of the stereogenic centres on the periphery of the macrocycles. The aggregation behaviour and chiroptical features of the aggregates are strongly dependent on the number of moieties decorating the periphery of the porphyrin framework. In particular, experimental evidence indicates that the structure of the steroid linker dictates the overall chirality of the supramolecular architectures. Moreover, the porphyrin concentration strongly affects the aggregation mechanism and the CD intensities of the spectra. Notably, AFM investigations reveal strong differences in aggregate morphology that are dependent on the nature of the appended functional groups, and closely in line with the changes in aggregation mechanism. The suprastructures formed at lower concentration show a network of long fibrous structures spanning over tens of micrometres, whereas the aggregates formed at higher concentration have smaller rodshaped structures that can be recognised as the result of coalescence of smaller globular structures. The fully steroid substituted derivative forms globular structures over the whole concentration range explored. Finally, a rationale for the aggregation phenomena was given by semiempirical calculations at the PM6 level

Multi-band magnetotransport in exfoliated thin films of Cu<i>_x</i>Bi₂Se₃

We report magnetotransport studies in thin (100nm indicating the presence of topologically protected surface states

Structural and vibrational study of Bi2Se3 under high pressure

The structural and vibrational properties of bismuth selenide (Bi2Se3) have been studied by means of x-ray diffraction and Raman scattering measurements up to 20 and 30 GPa, respectively. The measurements have been complemented with ab initio total-energy and lattice dynamics calculations. Our experimental results evidence a phase transition from the low-pressure rhombohedral (R-3m) phase (B-Bi2Se3) with sixfold coordination for Bi to a monoclinic C2/m structure (B-Bi2Se3) with sevenfold coordination for Bi above 10 GPa. The equation of state and the pressure dependence of the lattice parameters and volume of a and B phases of Bi2Se3 are reported. Furthermore, the presence of a pressure-induced electronic topological phase transition in B-Bi2Se3 is discussed. Raman measurements evidence that Bi2Se3 undergoes two additional phase transitions around 20 and 28 GPa, likely toward a monoclinic C2/c and a disordered body-centered cubic structure with 8-fold and 9- or 10-fold coordination, respectively. These two high-pressure structures are the same as those recently found at high pressures in Bi2Te3 and Sb2Te3. On pressure release, Bi2Se3 reverts to the original rhombohedral phase after considerable hysteresis. Symmetries, frequencies, and pressure coefficients of the Raman and infrared modes in the different phases are reported and discussed.This work was done under financial support from Spanish Ministry of Science and Innovation under Projects No. MAT2007-66129, No. MAT2010-21270-C04-03/04, and No. CSD-2007-00045 and from the Valencian government under Project No. Prometeo/2011-035. It is also supported by the Ministry of Education, Youth and Sports of the Czech Republic Project No. MSM 0021627501

Experimental and Theoretical Study of Bi2O2Se Under Compression

We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillén-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our results indicate that this compound exhibits considerable electronic changes around 4 GPa, likely related to the progressive shortening and hardening of the long and weak Bi–Se bonds linking the Bi2O2 and Se atomic layers. Variations of the structural, vibrational, and electronic properties induced by these electronic changes are discussed

High-pressure vibrational and optical study of Bi2Te3

We report an experimental and theoretical lattice dynamics study of bismuth telluride (Bi2Te3) up to 23 GPa together with an experimental and theoretical study of the optical absorption and reflection up to 10 GPa. The indirect bandgap of the low-pressure rhombohedral (R-3m) phase (α-Bi2Te3) was observed to decrease with pressure at a rate of −6 meV/GPa. In regard to lattice dynamics, Raman-active modes of α-Bi2Te3 were observed up to 7.4 GPa. The pressure dependence of their frequency and width provides evidence of the presence of an electronic-topological transition around 4.0 GPa. Above 7.4 GPa a phase transition is detected to the C2/m structure. On further increasing pressure two additional phase transitions, attributed to the C2/c and disordered bcc (Im-3m) phases, have been observed near 15.5 and 21.6 GPa in good agreement with the structures recently observed by means of x-ray diffraction at high pressures in Bi2Te3. After release of pressure the sample reverts back to the original rhombohedral phase after considerable hysteresis. Raman- and IR-mode symmetries, frequencies, and pressure coefficients in the different phases are reported and discussed.This work has been done under financial support from Spanish MICINN under projects MAT2008-06873-C02- 02, MAT2007-66129, Prometeo/2011-035, MAT2010-21270-C04-03/04, and CSD2007-00045 and supported by the Ministry of Education, Youth and Sports of the Czech Republic (MSM 0021627501)

Experimental and Theoretical Study of Bi2O2Se Under Compression

[EN] We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillen-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our results indicate that this compound exhibits considerable electronic changes around 4 GPa, likely related to the progressive shortening and hardening of the long and weak Bi-Se bonds linking the Bi2O2 and Se atomic layers. Variations of the structural, vibrational, and electronic properties induced by these electronic changes are discussed.This work was supported by Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) under project 201050/2012-9, by Spanish MINECO projects MAT2015-71070-REDC, MAT2016-75586-C4-1/2/3-P and CTQ2015-65207-P and by the Grant Agency of the Czech Republic (GA CR) under project 16-07711S. Supercomputer time has been provided by the Red Espanola de Supercomputacion (RES) and the MALTA cluster. D.S.-P. and J.A.S. acknowledge the "Ramon y Cajal" fellowship program (RYC-2015-17482) and Spanish Mineco Projects (2014-15643 and 2017-83295-P). J.R.-F. acknowledge the "Juan de la Cierva" program (IJCI-2014-20513) for financial support.Pereira, A.; Santamaría Pérez, D.; Ruiz Fuertes, J.; Manjón, F.; Cuenca Gotor, VP.; Vilaplana Cerda, RI.; Gomis, O.... (2018). Experimental and Theoretical Study of Bi2O2Se Under Compression. The Journal of Physical Chemistry C. 122(16):8853-8867. https://doi.org/10.1021/acs.jpcc.8b02194S885388671221