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The pressure-induced phase transition of the multiferroic manganese tungstate MnWO4 is studied on single crystals using synchrotron x-ray diffraction and Raman spectroscopy. We observe the monoclinic P2/c to triclinic P (1) over bar phase transition at 20.1 GPa and get insight on the phase transition mechanism from the appearance of tilted triclinic domains. Selective Raman spectroscopy experiments with single crystals have shown that the onset of the phase transition occurs 5 GPa below the previously reported pressure obtained from experiments performed with powder samples. ; The authors thank Professor M. M. Gospodinov from the Institute of Solid State Physics of Bulgaria for providing single-crystal samples of MnWO INF>4 /INF>. This research was partially supported by the Spanish government MINECO under Grant No. MAT2013-46649-C4-1/2-P and by Generalitat Valenciana Grants No. ACOMP-2013-1012 and No. ACOMP-2014-243. We acknowledge Diamond Light Source for time on beamline I15 under proposal EE6517 and I15 beamline scientist for technical support. DESY-Photon Science is gratefully acknowledged. PETRA III at DESY is a member of the Helmholtz Association (HGF). J.R.-F. thanks the Alexander von Humboldt Foundation for a postdoctoral fellowship and T. Bernert from the Max-Planck Institut fur Kohlenforschung for fruitful discussions. A.F. acknowledges financial support from the DFG within the priority program SPP1236 (Project No. FR2491/2-1), W.M. acknowledges the BMBF (Projects No. 05K10RFA and No. 05K13RF1), and J.A.S. acknowledges the MINECO for a Juan de la Cierva postdoctoral fellowship. ; Ruiz-Fuertes, J.; Friedrich, A.; Gomis, O.; Errandonea, D.; Morgenroth, W.; Sans Tresserras, JÁ.; Santamaria-Perez, D. (2015). High-pressure structural phase transition in MnWO4. Physical review B: Condensed matter and materials physics. 91(10):104109-1-104109-7. https://doi.org/10.1103/PhysRevB.91.104109 ; S ; 104109-1 ; 104109-7 ; 91 ; 10 ; Cheong, S.-W., & Mostovoy, M. (2007). Multiferroics: a magnetic twist for ...

Copyright (2011) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. ; We perform Raman-scattering measurements at high hydrostatic pressures on c-face and a-face InN layers to investigate the high-pressure behavior of the zone-center optical phonons of wurtzite InN. Linear pressure coefficients and mode Grneisen parameters are obtained, and the experimental results are compared with theoretical values obtained from ab initio lattice-dynamical calculations. Good agreement is found between the experimental and calculated results. © 2011 American Institute of Physics. ; Work supported by the Spanish MICINN (Projects MAT2010-16116, MAT2008-06873-C02-02, MAT2010-21270-C04-04, and CSD2007-00045), the Catalan Government (BE-DG 2009), and the Spanish Council for Research (PIE2009-CSIC). ; Ibanez, J.; Manjón Herrera, FJ.; Segura, A.; Oliva, R.; Cusco, R.; Vilaplana Cerda, RI.; Yamaguchi, T. (2011). High-pressure Raman scattering in wurtzite indium nitride. Applied Physics Letters. 99:119081-119083. https://doi.org/10.1063/1.3609327 ; S ; 119081 ; 119083 ; 99 ; Veal, T., McConville, C., & Schaff, W. (Eds.). (2009). Indium Nitride and Related Alloys. doi:10.1201/9781420078107 ; Gallinat, C. S., Koblmüller, G., Brown, J. S., Bernardis, S., Speck, J. S., Chern, G. D., … Wraback, M. (2006). In-polar InN grown by plasma-assisted molecular beam epitaxy. Applied Physics Letters, 89(3), 032109. doi:10.1063/1.2234274 ; Li, S. X., Wu, J., Haller, E. E., Walukiewicz, W., Shan, W., Lu, H., & Schaff, W. J. (2003). Hydrostatic pressure dependence of the fundamental bandgap of InN and In-rich group III nitride alloys. Applied Physics Letters, 83(24), 4963-4965. doi:10.1063/1.1633681 ; Gorczyca, I., Plesiewicz, J., Dmowski, L., Suski, T., Christensen, N. E., Svane, A., … Speck, J. S. (2008). Electronic structure and effective masses of InN under pressure. Journal of Applied Physics, 104(1), 013704. ...

High-pressure optical absorption measurements have been performed in defect chalcopyrite HgGa2Se4 to investigate the influence of pressure on the bandgap energy and its relation with the pressure-induced order-disorder processes that occur in this ordered-vacancy compound. Two different experiments have been carried out in which the sample undergoes either a partial or a total pressure-induced disorder process at 15.4 and 30.8GPa, respectively. It has been found that the direct bandgap energies of the recovered samples at 1GPa were around 0.15 and 0.23eV smaller than that of the original sample, respectively, and that both recovered samples have different pressure coefficients of the direct bandgap than the original sample. A comprehensive explanation for these results on the basis of pressure-induced order-disorder processes is provided. ; This study was supported by the Spanish government MEC under Grants No: MAT2010-21270-C04-01/03/04 and MAT2013-46649-C4-1/2/3-P, by MALTA Consolider Ingenio 2010 project (CSD2007-00045), by Generalitat Valenciana (GVA-ACOMP-2013-1012 and GVA-ACOMP-2014-243), and by the Vicerrectorado de Investigacion y Desarrollo of the Universitat Politecnica de Valencia (UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). E. P.-G., J. L.-S., P. R.-H, and A. M. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster. J.R.-F. thanks the Alexander von Humboldt foundation for a postdoctoral fellowship. ; Gomis, O.; Vilaplana Cerda, RI.; Manjón Herrera, FJ.; Ruiz-Fuertes, J.; Pérez-González, E.; López-Solano, J.; Bandiello, E. (2015). HgGa2Se4 under high pressure: an optical absorption study. physica status solidi (b). 252(9):2043-2051. https://doi.org/10.1002/pssb.201451714 ; S ; 2043 ; 2051 ; 252 ; 9 ; Bernard, J. E., & Zunger, A. (1988). Ordered-vacancy-compound semiconductors: PseudocubicCdIn2Se4. Physical Review B, 37(12), 6835-6856. doi:10.1103/physrevb.37.6835 ; Jiang, X., & Lambrecht, W. R. L. (2004). Electronic band structure of ordered ...

In this work, we report on high-pressure Raman scattering measurements in mercury digallium sulfide (HgGa2S4) with defect chalcopyrite structure that have been complemented with lattice dynamics ab initio calculations. Our measurements evidence that this semiconductor exhibits a pressure-induced phase transition from the completely ordered defect chalcopyrite structure to a partially disordered defect stannite structure above 18 GPa which is prior to the transition to the completely disordered rocksalt phase above 23 GPa. Furthermore, a completely disordered zincblende phase is observed below 5 GPa after decreasing pressure from 25 GPa. The disordered zincblende phase undergoes a reversible pressure-induced phase transition to the disordered rocksalt phase above 18 GPa. The sequence of phase transitions here reported for HgGa2S4 evidence the existence of an intermediate phase with partial cation-vacancy disorder between the ordered defect chalcopyrite and the disordered rocksalt phases and the irreversibility of the pressure-induced order-disorder processes occurring in ordered-vacancy compounds. The pressure dependence of the Raman modes of all phases, except the Raman-inactive disordered rocksalt phase, have been measured and discussed. ; This study was supported by the Spanish government MEC under Grant No: MAT2010-21270-C04-01/03/04, by MALTA Consolider Ingenio 2010 project (CSD2007-00045), and by the Vicerrectorado de Investigacion y Desarrollo of the Universidad Politecnica de Valencia (UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11). E. P.-G., P. R.-H., and A. M. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster. J.A.S. acknowledges Juan de la Cierva fellowship program for his financial support. ; Vilaplana Cerda, RI.; Robledillo, M.; Gomis Hilario, O.; Sans, J.; Manjón Herrera, FJ.; Pérez-González, E.; Rodríguez-Hernández, P. (2013). Vibrational study of HgGa2S4 under high pressure. Journal of Applied Physics. 113(9):935121-9351210. ...

Plasticizers are usually added to polymers to give them the desired flexibility and processability by changing the dynamical properties of the polymer chains. It is therefore important to give a quantitative description about how the dynamic behavior of a given polymer is modified by the incorporation of a second component. We analyze in this work, by means of dielectric spectroscopy, the dynamics of poly(vinyl acetate)/diethyl phthalate mixtures, at different concentrations, over a broad range of frequency, pressure, and temperature. The dynamics of these particular mixtures show only one main relaxation process contrarily to what is observed in athermal miscible polymer mixtures. From the dielectric spectra the maximum relaxation time as a function of pressure and temperature was obtained and analyzed. We studied the pressure dependence of the glass transition temperature as well as the fragility of both the neat components and the mixtures at different concentrations (on the rich polymer range). Finally, the experimental data were rationalized within the framework of an Adam–Gibbs (AG) based approach recently developed [G. A. Schwartz et al., J. Chem. Phys. 127, 154907 (2007)]. The model, originally developed for athermal blends, is here modified to take into account the non-negligible interaction between polymer and plasticizer. We found that the temperature-pressure dependence of the α-relaxation time is very well described by this AG extended model. ; The authors acknowledge support from the projects MAT2007-63681 and CSD2006-53, from the Spanish Ministry of Science and Innovation and IT-436-07, from the Basque Government. The support of the European Community within the Soft-Comp program is also acknowledged ; Peer reviewed

[EN] We report a joint experimental and theoretical study of the structural, vibrational, and electronic properties of layered monoclinic arsenic sulfide crystals (a-As2S3), aka mineral orpiment, under compression. X-ray diffraction and Raman scattering measurements performed on orpiment samples at high pressure and combined with ab initio calculations have allowed us to determine the equation of state and the tentative assignment of the symmetry of many Raman-active modes of orpiment. From our results, we conclude that no first-order phase transition occurs up to 25 GPa at room temperature; however, compression leads to an isostructural phase transition above 20 GPa. In fact, the As coordination increases from threefold at room pressure to more than fivefold above 20 GPa. This increase in coordination can be understood as the transformation from a solid with covalent bonding to a solid with metavalent bonding at high pressure, which results in a progressive decrease of the electronic and optical bandgap, an increase of the dielectric tensor components and Born effective charges, and a considerable softening of many high-frequency optical modes with increasing pressure. Moreover, we propose that the formation of metavalent bonding at high pressures may also explain the behavior of other group-15 sesquichalcogenides under compression. In fact, our results suggest that group-15 sesquichalcogenides either show metavalent bonding at room pressure or undergo a transition from p-type covalent bonding at room pressure towards metavalent bonding at high pressure, as a precursor towards metallic bonding at very high pressure. ; The authors are thankful for the financial support from Spanish Ministerio de Economia y Competitividad (MINECO) through MAT2016-75586-C4-2/3-P, FIS2017-83295-P and MALTA Consolider Team project (RED2018-102612-T). Also from Generalitat Valenciana under project PROMETEO/2018/123-EFIMAT. ELDS acknowledges the European Union FP7 People: Marie-Curie Actions programme for grant agreement No. ...

[EN] Gaseous time projection chambers (TPC) are a very attractive detector technology for particle tracking. Characterization of both drift velocity and di¿usion is of great importance to correctly assess their tracking capabilities. NEXT-White is a High Pressure Xenon gas TPC with electroluminescent ampli¿cation, a 1:2 scale model of the future NEXT-100detector, which will be dedicated to neutrinoless double beta decay searches. NEXT-White has been operating at Canfranc Underground Laboratory (LSC) since December2016. The drift parameters have been measured using 83mKr for a range of reduced drift ¿elds at two di¿erent pressure regimes, namely 7.2 bar and 9.1 bar. Theresults have been compared with Magboltz simulations. Agreement at the 5% level or better has been found for drift velocity, longitudinal di¿usion and transverse di¿usion. ; The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program SEV-2014-0398 and the Maria de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT and FEDER through the program COMPETE, projects PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and de-sc0017721 (University of Texas at Arlington); and the University of Texas at Arlington. We also warmly acknowledge the Laboratorio Nazionale di Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and ...

We report a joint experimental and theoretical study of the structural, vibrational, and electronic properties of layered monoclinic arsenic sulfide crystals (α-As2S3), aka mineral orpiment, under compression. X-ray diffraction and Raman scattering measurements performed on orpiment samples at high pressure and combined with ab initio calculations have allowed us to determine the equation of state and the tentative assignment of the symmetry of many Raman-active modes of orpiment. From our results, we conclude that no first-order phase transition occurs up to 25 GPa at room temperature; however, compression leads to an isostructural phase transition above 20 GPa. In fact, the As coordination increases from threefold at room pressure to more than fivefold above 20 GPa. This increase in coordination can be understood as the transformation from a solid with covalent bonding to a solid with metavalent bonding at high pressure, which results in a progressive decrease of the electronic and optical bandgap, an increase of the dielectric tensor components and Born effective charges, and a considerable softening of many high-frequency optical modes with increasing pressure. Moreover, we propose that the formation of metavalent bonding at high pressures may also explain the behavior of other group-15 sesquichalcogenides under compression. In fact, our results suggest that group-15 sesquichalcogenides either show metavalent bonding at room pressure or undergo a transition from p-type covalent bonding at room pressure towards metavalent bonding at high pressure, as a precursor towards metallic bonding at very high pressure. ; Authors thank the financial support from Spanish Ministerio de Economia y Competitividad (MINECO) through MAT2016-75586-C4-2/3-P and FIS2017-83295-P and from Generalitat Valenciana under project PROMETEO/2018/123-EFIMAT. ELDS acknowledges the European Union Horizon 2020 research and innovation programme under Marie Sklodowska-Curie for grant agreement No. 785789-COMEX. JAS also acknowledges Ramón y Cajal program for funding support through RYC-2015-17482. AM, SR and ELDS thank interesting discussions with J. Contreras-García who taught them how to analyze the ELF. Finally, authors thank ALBA Light Source for beam allocation at beamline MSPD (Experiment No. 2013110699) and acknowledge computing time provided by MALTA-Cluster and Red Española de Supercomputación (RES) through computer resources at MareNostrum with technical support provided by the Barcelona Supercomputing Center (QCM-2018-3-0032). ; Peer reviewed