Effect of isotopic mass on the photoluminescence spectra of beta zinc sulfide

Zinc sulfide is a wide bandgap semiconductor which crystallizes in either the wurtzite modification (a-ZnS), the zincblende modification (b-ZnS) or as one of several similar tetrahedrally coordinated polytypes. In this work, we report a photoluminescence study of different samples of isotopically pure b-ZnS crystals, and crystals with the natural isotopic abundances, at 15 and 77 K. The derivatives of the free and bound exciton energies on isotopic mass have been obtained. They allow us to estimate the contribution of the zinc and sulfur vibrations to the bandgap renormalization energy by electron-phonon interaction. A two-oscillator model based on the zinc and sulfur renormalization energies has been used to account for the temperature dependence of the bandgap energy in ZnS. The results are compared with those found for other tetrahedrally coordinated semiconductors.Comment: 19 pages, 4 Postscript figures, sent to Solid State Communication

High-pressure lattice-dynamics of NdVO4

High-pressure Raman-scattering measurements and ab initio calculations on NdVO4 have been carried out up to 30 GPa. Our combined experimental and theoretical study confirms that beyond 5.9 GPa NdVO4 undergoes an irreversible zircon to monazite transition. The coexistence of zircon and monazite phases is experimentally observed up to ~8 GPa (which agrees with the theoretical transition pressure), stabilizing the monazite phase as a single phase around 10 GPa. Calculations additionally predict the existence of a second high-pressure phase transition at 12.4 GPa. This reversible phase transition has been experimentally observed beyond 18.1 GPa and remains stable up to 30 GPa. The post-monazite phase is predicted to have a monoclinic structure isomorphic to the BaWO4-II type structure. The calculated structure for the three polymorphs of NdVO4 is reported and the pressure dependence of their Raman modes is discussed

Effects of pressure on the local atomic structure of CaWO4 and YLiF4: Mechanism of the scheelite-to-wolframite and scheelite-to-fergusonite transitions

The pressure response of the scheelite phase of CaWO4 (YLiF4) and the occurrence of the pressure induced scheelite-to-wolframite (M-fergusonite) transition are reviewed and discussed. It is shown that the change of the axial parameters under compression is related with the different pressure dependence of the W-O (Li-F) and Ca-O (Y-F) interatomic bonds. Phase transition mechanisms for both compounds are proposed. Furthermore, a systematic study of the phase transition in 16 different scheelite ABX4 compounds indicates that the transition pressure increases as the packing ratio of the anionic BX4 units around the A cations increases.Comment: 38 pages, 10 figures (Figure 5 corrected), accepted for publication in Journal of Solid State Chemistr

ZnO-based spinels grown by electrodeposition

We report on the synthesis of thin films of ZnCo 2O 4 and ZnMn 2O 4 spinels, as well as pure Co 3O 4 and Mn 3O 4 spinels, by means of electrodeposition. Spinel thin films have been analyzed by energy dispersive spectroscopy, X-ray diffraction, and Raman spectroscopy. We show that under determined deposition conditions the initial wurtzite structure of Co- and Mn-doped ZnO develops into spinel structures when the Co and Mn concentration in the films is above the solubility limit of these ions in the typical ZnO-wurtzite structure. © 2012 Elsevier Ltd. All rights reserved.This work was supported by Spanish Government through MICINN grants MAT2009-14625-C03-03, MAT2010-21270-C04-04 and MALTA CSD2007-0045. Financial support by the European Commission through NanoCIS project (PIRSES-GA-2010-269279) is gratefully acknowledged. Finally, we also want to acknowledge the support of Vicerrectorado de Investigacion y Desarrollo de la Universitat Politecnica de Valencia through projects UPV2011-0914 PAID-05-11 and UPV2011-0966 PAID-06-11.Tortosa Jorques, MD.; Manjón Herrera, FJ.; Mollar García, MA.; Marí Soucase, B. (2012). ZnO-based spinels grown by electrodeposition. Journal of Physics and Chemistry of Solids. 73(9):1111-1115. https://doi.org/10.1016/j.jpcs.2012.04.002S1111111573

Crystal structure of HgGa2Se4 under compression

We report on high-pressure x-ray diffraction measurements up to 17.2 GPa in mercury digallium selenide (HgGa2Se4). The equation of state and the axial compressibilities for the low-pressure tetragonal phase have been determined and compared to related compounds. HgGa2Se4 exhibits a phase transition on upstroke toward a disordered rock-salt structure beyond 17 GPa, while on downstroke it undergoes a phase transition below 2.1 GPa to a phase that could be assigned to a metastable zinc-blende structure with a total cation-vacancy disorder. Thermal annealing at low- and high-pressure shows that kinetics plays an important role on pressure-driven transitions.This study was supported by the Spanish government MEC under grants nos: MAT2010-21270-C04-01/03/04 and CTQ2009-14596-C02-01, by the Comunidad de Madrid and European Social Fund (S2009/PPQ-1551 4161893), 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., J.L.-S., A.M., and P.R.-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster.Gomis Hilario, O.; Vilaplana Cerda, RI.; Manjón, F.; Santamaría Pérez, D.; Errandonea, D.; Pérez González, E.; López Solano, J.... (2013). Crystal structure of HgGa2Se4 under compression. Materials Research Bulletin. 48:2128-2133. https://doi.org/10.1016/j.materresbull.2013.02.037S212821334

Structural and Vibrational Properties of Corundum-type In2O3 Nanocrystals under Compression

This work reports the structural and vibrational properties of nanocrystals of corundum-type In2O3 (rh-In2O3) at high pressures by using angle-dispersive x-ray diffraction and Raman scattering measurements up to 30 GPa. The equation of state and the pressure dependence of the Raman-active modes of the corundum phase in nanocrystals are in good agreement with previous studies on bulk material and compare nicely with theoretical simulations on bulk rh-In2O3. Nanocrystalline rh-In2O3 showed stability under compression at least up to 20 GPa, unlike bulk rh-In2O3 which gradually transforms to the orthorhombic Pbca (Rh2O3-III-type) structure above 12-14 GPa. The different stability range found in nanocrystalline and bulk In2O3 is discussed

Structural and electrical study of the topological insulator SnBi2Te4 at high pressures

We report high-pressure X-ray diffraction and electrical measurements of the topological insulator SnBi2Te4 at room temperature. The pressure dependence of the structural properties of the most stable phase of SnBi2Te4 at ambient conditions (trigonal phase) have been experimentally determined and compared with results of our ab initio calculations. Furthermore, a comparison of SnBi2Te4 with the parent compound Bi2Te3 shows that the central TeSnTe trilayer, which substitutes the Te layer at the center of the TeBiTeBiTe layers of Bi2Te3, plays a minor role in the compression of SnBi2Te4. Similar to Bi2Te3, our resistance measurements and electronic band structure simulations in SnBi2Te4 at high pressure suggest that this compound exhibits a pressure-induced electronic topological transition or Lifshitz transition between 3.5 and 5.0 GPa. (C) 2016 Published by Elsevier B.V.We thank Dr. Philipp Urban for preparing the sample. This work has been performed under financial support from Spanish MINECO under projects MAT2013-46649-C4-2-P, MAT2015-71070-REDC and CTQ2015-67755-C2-1-R and from Spanish Ministerio de Educacion, Cultura y Deporte as part of "Programa Campus de Excelencia Internacional/Programa de Valoracion y Recursos Conjuntos de I + D + i VLC/CAMPUS" through projects SP20140701 and SP20140871. One of the experiments were performed at MSPD-BL04 beamline at ALBA Synchrotron with the collaboration of ALBA staff. J.A.S. thanks "Juan de la Cierva" fellowship program for funding. A. A.-C. and J.S.-B. are also grateful to Spanish MINECO for the FPI (BES-2013-066112) and Ramon y Cajal (RyC-2010-06276) fellowships. We acknowledge Diamond Light Source for time on beamline I15 under Proposal EE9102.Vilaplana Cerda, RI.; Sans Tresserras, JÁ.; Manjón Herrera, FJ.; Andrada-Chacón, A.; Sánchez-Benitez, J.; Popescu, C.; Gomis, O.... (2016). Structural and electrical study of the topological insulator SnBi2Te4 at high pressures. Journal of Alloys and Compounds. 685:962-970. https://doi.org/10.1016/j.jallcom.2016.06.170S96297068

Structural and elastic properties of defect chalcopyrite HgGa2S4 under high pressure

In this work, we focus on the study of the structural and elastic properties of mercury digallium sulfide (HgGa2S4) at high pressures. This compound belongs to the family of AB(2)X(4) ordered-vacancy compounds and exhibits a tetragonal defect chalcopyrite structure. X-ray diffraction measurements at room temperature have been performed under compression up to 15.1 GPa in a diamond anvil cell. Our measurements have been complemented and compared with ab initio total energy calculations. The axial compressibility and the equation of state of the low-pressure phase of HgGa2S4 have been experimentally and theoretically determined and compared to other related ordered-vacancy compounds. The pressure dependence of the theoretical cation-anion and vacancy-anion distances and compressibilities in HgGa2S4 are reported and discussed in comparison to other related ordered-vacancy compounds. Finally, the pressure dependence of the theoretical elastic constants and elastic moduli of HgGa2S4 has been studied. Our calculations indicate that the low-pressure phase of HgGa2S4 becomes mechanically unstable above 13.8 GPa. (C) 2013 Elsevier B. V. All rights reserved.This study was supported by the Spanish government MEC under Grants No: MAT2010-21270-C04-01/03/04 and CTQ2009-14596-C02-01, by the Comunidad de Madrid and European Social Fund (S2009/PPQ-1551 4161893), by MALTA Consolider Ingenio 2010 Project (CSD2007-00045), by Generalitat Valenciana (GVA-ACOMP-2013-1012), 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., A. M., and P.R-H. acknowledge computing time provided by Red Espa ola de Supercomputacion (RES) and MALTA-Cluster. J.A.S. acknowledges Juan de la Cierva fellowship program for financial support.Gomis Hilario, O.; Santamaría-Pérez, D.; Vilaplana Cerda, RI.; Luna Molina, R.; Sans, JA.; Manjón Herrera, FJ.; Errandonea, D.... (2014). Structural and elastic properties of defect chalcopyrite HgGa2S4 under high pressure. Journal of Alloys and Compounds. 583:70-78. https://doi.org/10.1016/j.jallcom.2013.08.123S707858

Elastic and thermodynamic properties of alpha-Bi2O3 at high pressures: Study of mechanical and dynamical stability

[EN] The elastic and thermodynamic properties of the monoclinic polymorph of bismuth oxide (alpha-Bi2O3); aka mineral bismite, have been theoretically investigated both at room pressure and under hydrostatic compression by means of first principles calculations based on density functional theory. In this work, the elastic stiffness coefficients, elastic moduli, Poisson's ratio, B/G ratio, elastic anisotropy indexes (A(B), A(G), A(1), A(2), A(3), Au) and directional dependence of Young modulus and linear compressibility have been obtained. Vickers hardness, and sound wave velocities have been calculated. Our simulations show that bismite has a high elastic anisotropy. alpha-Bi2O3 is a ductile material whose elastic anisotropy increases under compression and presents a stronger ability to resist volume compression than shear deformation at all pressures. Besides, it has a very small minimum thermal conductivity, which is well suited for thermoelectric applications. Finally, the mechanical and dynamical stability of bismite at high pressure has been studied and it has been found that alpha-Bi2O3 becomes mechanically unstable at pressures beyond 19.3 GPa and dynamically unstable above 11.5 GPa. These instabilities could be responsible for the amorphization of bismite observed experimentally between 15 and 20 GPa.This research was supported by the Spanish Ministerio de Economia y Competitividad under Projects MAT2016-75586-C4-2-P/3-P and MAT2015-71070-REDC. P.R.-H. and A.M. acknowledge Red Espanola de SupercomputaciOn (RES) and MALTA-Cluster for the computing time.Gomis, O.; Manjón, F.; Rodríguez-Hernández, P.; Muñoz, A. (2019). Elastic and thermodynamic properties of alpha-Bi2O3 at high pressures: Study of mechanical and dynamical stability. Journal of Physics and Chemistry of Solids. 124:111-120. https://doi.org/10.1016/j.jpcs.2018.09.002S11112012

InBO3 and ScBO3 at high pressures: an ab initio study of elastic and thermodynamic properties

We have theoretically investigated the elastic properties of calcite-type orthoborates ABO(3) (A= Sc and In) at high pressure by means of ab initio total-energy calculations. From the elastic stiffness coefficients, we have obtained the elastic moduli (B, G and E), Poisson's ratio (nu), B/G ratio, universal elastic anisotropy index (A(U)), Vickers hardness, and sound wave velocities for both orthoborates. Our simulations show that both borates are more resistive to volume compression than to shear deformation (B > G). Both compounds are ductile and become more ductile, with an increasing elastic anisotropy, as pressure increases. We have also calculated some thermodynamic properties, like Debye temperature and minimum thermal conductivity. Finally, we have evaluated the theoretical mechanical stability of both borates at high hydrostatic pressures. It has been found that the calcite-type structure of InBO3 and ScBO3 becomes mechanically unstable at pressures beyond 56.2 and 57.7 GPa, respectively. (C) 2016 Elsevier Ltd. All rights reserved.This study is supported by the Spanish MICINN projects MAT2013-46649-C4-2-P/3-P and MAT2015-71070-REDC. H.M.O., A.M., and P.R-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster. J.A.S. acknowledges Juan de la Cierva fellowship program for financial support.Gomis, O.; Ortiz, HM.; Sans Tresserras, JÁ.; Manjón Herrera, FJ.; Santamaría-Pérez, D.; Rodríguez-Hernández, P.; Muñoz, A. (2016). InBO3 and ScBO3 at high pressures: an ab initio study of elastic and thermodynamic properties. Journal of Physics and Chemistry of Solids. 98:198-208. https://doi.org/10.1016/j.jpcs.2016.07.002S1982089