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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Layered topological semimetal GaGeTe: New polytype with non-centrosymmetric structure

[EN] GaGeTe is a layered van der Waals material composed of germanene and GaTe sublayers that has been recently predicted to be a basic Z2 topological semimetal. To date, only one polytype of GaGeTe is known with trigonal centrosymmetric structure (a phase, space group R-3m, No. 166). Here we show that asgrown samples of GaGeTe show traces of at least another polytype with hexagonal noncentrosymmetric structure (f3 phase, space group P63mc, No. 186). Moreover, we suggest that another bulk hexagonal polytype (g phase, space group P-3m1, No. 164) could also be found near room conditions. Both a and f3 polytypes have been identified and characterized by means of X-ray diffraction and Raman scattering measurements with the support of ab initio calculations. We provide the vibrational properties of both polytypes and show that the Raman spectrum reported for GaGeTe almost forty years ago and attributed to the a phase, was, in fact, that of the secondary f3 phase. Additionally, we show that a Fermi resonance occurs in a-GaGeTe under non-resonant excitation conditions, but not under resonant excitation conditions. Theoretical calculations show that bulk f3-GaGeTe is a non-centrosymmetric weak topological semimetal with even smaller lattice thermal conductivity than centrosymmetric bulk aGaGeTe. In perspective, our work paves the way for the control and engineering of GaGeTe polytypes to design and implement complex van der Waals heterostructures formed by a combination of centrosymmetric and non-centrosymmetric layers of up to three different polytypes in a single material, suitable for a number of fundamental studies and technological applications.This publication is part of the project MALTA Consolider Team network (RED2018-102612-T) , financed by MINECO/AEI/10.13039/501100003329; by I ? D ? i projects PID2019-106383 GB -41/42/43 financed by MCIN/AEI/10.13039/501100011033; and by project PROMETEO/2018/123 (EFIMAT) financed by Generalitat Valenciana. E.B. would like to thank the Universitat Politecnica de Valencia for his postdoctoral contract (Ref. PAID -10-21) . AHR was supported by the U.S. Department of Energy (DOE) , Office of Science, Basic Energy Sciences under award DE-SC0021375. We also acknowledge the computational resources awarded by XSEDE, a project supported by National Science Foundation grant number ACI-1053575. The authors also acknowledge the support from the Texas Advances Computer Center (with the Stampede2 and Bridges supercom- puters) . E.L.d.S would like to acknowledge the Network of Extreme Conditions Laboratories (NECL) , financed by FCT and co -financed by NORTE 2020, through the program Portugal 2020 and FEDER; the High Performance Computing Chair-a R & D infrastructure (based at the University of ? Evora; PI: M. Avillez) ; and for the computational support provided by the HPC center OBLIVION -U. ? Evora to perform the lattice thermal conductivity calculations. A.L. and D.E. would like to thank the Generalitat Valenciana for the Ph.D. Fellowship no. GRISOLIAP/2019/025.Gallego-Parra, S.; Bandiello, E.; Liang, A.; Da Silva, EL.; Rodriguez-Hernandez, P.; Muñoz, A.; Radescu, S.... (2022). Layered topological semimetal GaGeTe: New polytype with non-centrosymmetric structure. Materials Today Advances. 16:1-16. https://doi.org/10.1016/j.mtadv.2022.1003091161

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

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)

Structural, vibrational, and electronic behavior of two GaGeTe polytypes under compression

[EN] GaGeTe is a layered topological semimetal that has been recently found to exist in at least two different polytypes, a-GaGeTe (R3m) and b-GaGeTe (P63mc). Here we report a joint experimental and theoretical study of the structural, vibrational, and electronic properties of these two polytypes in high-pressure conditions. Both polytypes show anisotropic compressibility and two phase transitions, above 7 and 15 GPa, respectively, as confirmed by XRD and Raman spectroscopy measurements. Although the nature of the high-pressure phases could not be confirmed, comparison with other chalcogenides and total -energy calculations allow us to propose possible high-pressure phases for both polytypes with an in-crease in coordination for Ga and Ge atoms from 4 to 6. In particular, the simplification of the X-ray pattern for both polytypes above 15 GPa suggests a transition to a structure of relatively higher symmetry than the original one. This result is consistent with the rocksalt-like high-pressure phases observed in parent III-VI semiconductors, such as GaTe, GaSe, and InSe. Pressure-induced amorphization is observed upon pressure release. The electronic band structures of a-GaGeTe and b-GaGeTe and their pressure dependence also show similarities to III-VI semiconductors, thus suggesting that the germanene-like sublayer induces a semimetallic character in both GaGeTe polytypes. Above 3 GPa, both polytypes lose their topological features, due to the opening of the direct band gap, while the reduction of the interlayer space increases the thermal conductivity at high pressure. & COPY; 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).This publication is part of the project MALTA Consolider Team Network (RED2022-134388-T) , financed by MINECO/AEI/10.13039/501100003329; by I+D+i projects PID2019-106383GB-41/42/43, FIS2017-83295-P and PID2021-125927NB-C2 financed by MCIN/AEI/10.13039/501100011033; and by project PROMETEO CIPROM/2021/075 (GREENMAT) , financed by Generalitat Valenciana. This study forms part of the Advanced Materials program and is supported by MCIN with funding from European UnionNextGeneration EU (PRTR-C17.I1) and by Generalitat Valenciana through projects MFA/2022/007 and MFA/2022/025 (ARCANGEL) . J.A.S. acknowledges the Ramon y Cajal fellowship (RYC-2015-17482) for financial support. E.B. acknowledges the Universitat Politecnica de Valencia for his postdoctoral contract (program PAID-10-21) . We thank V. Monteseguro (Universidad de Cantabria) and Dr. H. Osman (Universidad de Valencia) for the fruitful discussions on the subject. Authors thank the ALBA Synchrotron for the XRD experiments performed at the MSPD beamline with the collaboration of ALBA staff (proposals No. 2015021222 and 2020074395) as well as the Elettra Sincrotrone Trieste for XRD experiments performed at the XPRESS beamline (proposal 20215005, in-house experiment) . Finally, the authors acknowledge the computing time provided by MALTA Cluster and Red Espanola de Supercomputacion (RES) . E.Ld.S. acknowledges the High Performance Computing Chair-a R & amp;D infrastructure (based at the University of ?Evora; PI: M. Avillez) ,endorsed by Hewlett Packard Enterprise, and involving a con-sortium of higher education institutions, research centers, enter-prises, and public/private organizations; and the Portuguese Foundation of Science and Technology for the financial support with the CEEC individual fellowship 5th edition, Reference 2022.00082.CEECIND.Bandiello, E.; Gallego-Parra, S.; Liang, A.; Sans-Tresserras, JÁ.; Cuenca-Gotor, VP.; Lora Da Silva, E.; Vilaplana Cerda, RI.... (2023). Structural, vibrational, and electronic behavior of two GaGeTe polytypes under compression. Materials Today Advances. 19. https://doi.org/10.1016/j.mtadv.2023.1004031

Study of montelukast in children with sickle cell disease (SMILES): a study protocol for a randomised controlled trial

BACKGROUND: Young children with sickle cell anaemia (SCA) often have slowed processing speed associated with reduced brain white matter integrity, low oxygen saturation, and sleep-disordered breathing (SDB), related in part to enlarged adenoids and tonsils. Common treatments for SDB include adenotonsillectomy and nocturnal continuous positive airway pressure (CPAP), but adenotonsillectomy is an invasive surgical procedure, and CPAP is rarely well-tolerated. Further, there is no current consensus on the ability of these treatments to improve cognitive function. Several double-blind, randomised controlled trials (RCTs) have demonstrated the efficacy of montelukast, a safe, well-tolerated anti-inflammatory agent, as a treatment for airway obstruction and reducing adenoid size for children who do not have SCA. However, we do not yet know whether montelukast reduces adenoid size and improves cognition function in young children with SCA. METHODS: The Study of Montelukast In Children with Sickle Cell Disease (SMILES) is a 12-week multicentre, double-blind, RCT. SMILES aims to recruit 200 paediatric patients with SCA and SDB aged 3-7.99 years to assess the extent to which montelukast can improve cognitive function (i.e. processing speed) and sleep and reduce adenoidal size and white matter damage compared to placebo. Patients will be randomised to either montelukast or placebo for 12 weeks. The primary objective of the SMILES trial is to assess the effect of montelukast on processing speed in young children with SCA. At baseline and post-treatment, we will administer a cognitive evaluation; caregivers will complete questionnaires (e.g. sleep, pain) and measures of demographics. Laboratory values will be obtained from medical records collected as part of standard care. If a family agrees, patients will undergo brain MRIs for adenoid size and other structural and haemodynamic quantitative measures at baseline and post-treatment, and we will obtain overnight oximetry. DISCUSSION: Findings from this study will increase our understanding of whether montelukast is an effective treatment for young children with SCA. Using cognitive testing and MRI, the SMILES trial hopes to gain critical knowledge to help develop targeted interventions to improve the outcomes of young children with SCA. TRIAL REGISTRATION: ClinicalTrials.gov NCT04351698 . Registered on April 17, 2020. European Clinical Trials Database (EudraCT No. 2017-004539-36). Registered on May 19, 2020