Isotope effects on the lattice parameter of cubic SiC

Path-integral molecular dynamics simulations in the isothermal-isobaric (NPT) ensemble have been carried out to study the dependence of the lattice parameter of 3C-SiC upon isotope mass. This computational method allows a quantitative and nonperturbative study of such anharmonic effect. Atomic nuclei were treated as quantum particles interacting via a tight-binding-type potential. At 300 K, the difference Delta a between lattice parameters of 3C-SiC crystals with 12C and 13C amounts to 2.1 x 10^{-4} A. The effect due to Si isotopes is smaller, and amounts to 3.5 x 10^{-5} A when replacing 28Si by 29Si. Results of the PIMD simulations are interpreted in terms of a quasiharmonic approximation for the lattice vibrations.Comment: 4 pages, 3 figure

Borates or phosphates? That is the question

[EN] Chemical nomenclature is perceived to be a closed topic. However, this work shows that the identification of polyanionic groups is still ambiguous and so is the nomenclature for some ternary compounds. Two examples, boron phosphate (BPO4) and boron arsenate (BAsO4), which were assigned to the large phosphate and arsenate families, respectively, nearly a century ago, are explored. The analyses show that these two compounds should be renamed phosphorus borate (PBO4) and arsenic borate (AsBO4). Beyond epistemology, this has pleasing consequences at several levels for the predictive character of chemistry. It paves the way for future work on the possible syntheses of SbBO4 and BiBO4, and it also renders previous structure field maps completely predictive, allowing us to foresee the structure and phase transitions of NbBO4 and TaBO4. Overall, this work demonstrates that quantum mechanics calculations can contribute to the improvement of current chemical nomenclature. Such revisitation is necessary to classify compounds and understand their properties, leading to the main final aim of a chemist: predicting new compounds, their structures and their transformations.This research was partially supported by Spanish MINECO (grant Nos. MAT2015-71070-REDC and MAT2016-75586-C4-2-P, and MALTA Consolider Team RED2018-102612-T) and Generalitat Valenciana (grant No. PROMETEO/2018/123-EFIMAT). J. Contreras-Garci ' a thanks CALSIMLAB (public grant No. ANR-11-LABX-0037-01), overseen by the French National Research Agency (ANR) as part of the Investissements d'Avenir program (grant No. ANR-11-IDEX-0004-02). M. Marque ' s acknowledges support from the ERC grant `Hecate' and computational resources provided by the UKCP consortium under EPSRC grant EP/P022561/1.Contreras-García, J.; Izquierdo-Ruiz, F.; Marqués, M.; Manjón, F. (2020). Borates or phosphates? That is the question. Acta Crystallographica Section A: Foundations and Advances. 76:197-205. https://doi.org/10.1107/S2053273319016826S19720576Abraham, R. H. & Marsden, J. E. (1994). Foundations of Mechanics. Reading: Addison Wesley.Alinger, N. L., Clark, T., Gasteiger, J., Kollman, P. A., Schaefer, H. F. III, Schreiner, P. R. & Schleyer, von R. (1998). Encyclopedia of Computational Chemistry, edited by R. F. W. Bader. Chichester: Wiley.Bader, R. F. W. (1990). Atoms in Molecules, a Quantum Theory. Oxford: Clarendon.Bader, R. F. W. (1994). Principle of stationary action and the definition of a proper open system. Physical Review B, 49(19), 13348-13356. doi:10.1103/physrevb.49.13348Bastide, J. P. (1987). Systématique simplifiée des composés ABX4 (X = O2−, F−) et evolution possible de leurs structures cristallines sous pression. Journal of Solid State Chemistry, 71(1), 115-120. doi:10.1016/0022-4596(87)90149-6Bayer, G. (1972). Thermal expansion of ABO4-compounds with zircon- and scheelite structures. Journal of the Less Common Metals, 26(2), 255-262. doi:10.1016/0022-5088(72)90045-8Blasse, G., & Van Den Heuvel, G. P. M. (1973). Some optical properties of tantalum borate (tabo4), a compound with unusual coordinations. Physica Status Solidi (a), 19(1), 111-117. doi:10.1002/pssa.2210190109Boyd, R. J. & Matta, C. F. (2007). Editors. The Quantum Theory of Atoms in Molecules. From Solid State to DNA and Drug Design. Weinheim: Wiley-VCH.Brill, R., & Debretteville, A. P. (1955). On the chemical bond type in AlPO4. Acta Crystallographica, 8(9), 567-570. doi:10.1107/s0365110x5500176xDachille, F., & Glasser, L. S. D. (1959). High pressure forms of BPO4 and BAsO4; quartz analogues. Acta Crystallographica, 12(10), 820-821. doi:10.1107/s0365110x59002365Dachille, F., & Roy, R. (1959). High-pressure region of the silica isotypes. Zeitschrift für Kristallographie, 111(1-6), 451-461. doi:10.1524/zkri.1959.111.1-6.451Demartin, F., Diella, V., Gramaccioli, C. M., & Pezzotta, F. (2001). Schiavinatoite, (Nb,Ta)BO4, the Nb analogue of behierite. European Journal of Mineralogy, 13(1), 159-165. doi:10.1127/0935-1221/01/0013-0159Depero, L. E., & Sangaletti, L. (1997). Cation Sublattice and Coordination Polyhedra inABO4Type of Structures. Journal of Solid State Chemistry, 129(1), 82-91. doi:10.1006/jssc.1996.7234Errandonea, D., & Manjón, F. J. (2008). Pressure effects on the structural and electronic properties of ABX4 scintillating crystals. Progress in Materials Science, 53(4), 711-773. doi:10.1016/j.pmatsci.2008.02.001Fukunaga, O., & Yamaoka, S. (1979). Phase transformations in ABO 4 type compounds under high pressure. Physics and Chemistry of Minerals, 5(2), 167-177. doi:10.1007/bf00307551Gázquez, J. L., & Ortiz, E. (1984). Electronegativities and hardnesses of open shell atoms. The Journal of Chemical Physics, 81(6), 2741-2748. doi:10.1063/1.447946Geerlings, P., De Proft, F., & Langenaeker, W. (2003). Conceptual Density Functional Theory. Chemical Reviews, 103(5), 1793-1874. doi:10.1021/cr990029pGenoni, A., Bučinský, L., Claiser, N., Contreras‐García, J., Dittrich, B., Dominiak, P. M., … Grabowsky, S. (2018). Quantum Crystallography: Current Developments and Future Perspectives. Chemistry – A European Journal, 24(43), 10881-10905. doi:10.1002/chem.201705952Gibbs, G. V., Cox, D. F., Boisen, M. B., Downs, R. T., & Ross, N. L. (2003). The electron localization function: a tool for locating favorable proton docking sites in the silica polymorphs. Physics and Chemistry of Minerals, 30(5), 305-316. doi:10.1007/s00269-003-0318-2Gramaccioli, C. M. (2000). Un nuovo minerale: la schiavinatoite. Rendiconti Lincei, 11(4), 197-199. doi:10.1007/bf02904665Haines, J., Chateau, C., Léger, J. M., Bogicevic, C., Hull, S., Klug, D. D., & Tse, J. S. (2003). Collapsing Cristobalitelike Structures in Silica Analogues at High Pressure. Physical Review Letters, 91(1). doi:10.1103/physrevlett.91.015503Hazen, R. M., & Finger, L. W. (1979). Bulk modulus-volume relationship for cation-anion polyhedra. Journal of Geophysical Research: Solid Earth, 84(B12), 6723-6728. doi:10.1029/jb084ib12p06723Hazen, R. M., Finger, L. W., & Mariathasan, J. W. E. (1985). High-pressure crystal chemistry of scheelite-type tungstates and molybdates. Journal of Physics and Chemistry of Solids, 46(2), 253-263. doi:10.1016/0022-3697(85)90039-3IUPAC (1970). Nomenclature of Inorganic Solids. Definitive Rules. 3rd ed. London: International Union of Pure and Applied Chemistry.Kniep, R., Gözel, G., Eisenmann, B., Röhr, C., Asbrand, M., & Kizilyalli, M. (1994). Borophosphates—A Neglected Class of Compounds: Crystal Structures of MII[BPO5](MII Ca, Sr) and Ba3[BP3O12]. Angewandte Chemie International Edition in English, 33(7), 749-751. doi:10.1002/anie.199407491Kresse, G., & Joubert, D. (1999). From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B, 59(3), 1758-1775. doi:10.1103/physrevb.59.1758Lashin, V. E., Khritokhin, N. A., & Andreev, O. V. (2012). Structure maps of ABX4 inorganic compounds. Russian Journal of Inorganic Chemistry, 57(12), 1584-1587. doi:10.1134/s0036023612120133Léger, J. M., Haines, J., Chateau, C., Bocquillon, G., Schmidt, M. W., Hull, S., … Marchand, R. (2001). Phosphorus oxynitride PON, a silica analogue: structure and compression of the cristobalite-like phase; P  - T phase diagram. Physics and Chemistry of Minerals, 28(6), 388-398. doi:10.1007/s002690100161Liu, L. (1982). Phase transformations in MSiO4 compounds at high pressures and their geophysical implications. Earth and Planetary Science Letters, 57(1), 110-116. doi:10.1016/0012-821x(82)90177-7Martín Pendás, A., Costales, A., Blanco, M. A., Recio, J. M., & Luaña, V. (2000). Local compressibilities in crystals. Physical Review B, 62(21), 13970-13978. doi:10.1103/physrevb.62.13970Monkhorst, H. J., & Pack, J. D. (1976). Special points for Brillouin-zone integrations. Physical Review B, 13(12), 5188-5192. doi:10.1103/physrevb.13.5188Mori-Sánchez, P., Pendás, A. M., & Luaña, V. (2001). Polarity inversion in the electron density of BP crystal. Physical Review B, 63(12). doi:10.1103/physrevb.63.125103Muller, O., & Roy, R. (1973). Phase transitions among the ABX4compounds*,1. Zeitschrift für Kristallographie, 138(138), 237-253. doi:10.1524/zkri.1973.138.138.237O’Keeffe, M., & Hyde, B. G. (1976). Cristobalites and topologically-related structures. Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 32(11), 2923-2936. doi:10.1107/s0567740876009308Otero-de-la-Roza, A., Blanco, M. A., Pendás, A. M., & Luaña, V. (2009). Critic: a new program for the topological analysis of solid-state electron densities. Computer Physics Communications, 180(1), 157-166. doi:10.1016/j.cpc.2008.07.018Otero-de-la-Roza, A., Johnson, E. R., & Contreras-García, J. (2012). Revealing non-covalent interactions in solids: NCI plots revisited. Physical Chemistry Chemical Physics, 14(35), 12165. doi:10.1039/c2cp41395gPauling, L. (1929). THE PRINCIPLES DETERMINING THE STRUCTURE OF COMPLEX IONIC CRYSTALS. Journal of the American Chemical Society, 51(4), 1010-1026. doi:10.1021/ja01379a006Pauling, L. (1960). The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry, 3rd ed., pp. 543-562. Ithaca: Cornell University Press.Perdew, J. P., Burke, K., & Ernzerhof, M. (1996). Generalized Gradient Approximation Made Simple. Physical Review Letters, 77(18), 3865-3868. doi:10.1103/physrevlett.77.3865Rahm, M., Zeng, T., & Hoffmann, R. (2018). Electronegativity Seen as the Ground-State Average Valence Electron Binding Energy. Journal of the American Chemical Society, 141(1), 342-351. doi:10.1021/jacs.8b10246Range, K.-J., Wildenauer, M., & Heyns, A. M. (1988). Extremely Short Non-Bonding Oxygen?Oxygen Distances: The Crystal Structures of NbBO4, NaNb3O8, and NaTa3O8. Angewandte Chemie International Edition in English, 27(7), 969-971. doi:10.1002/anie.198809691Recio, J. M., Franco, R., Martín Pendás, A., Blanco, M. A., Pueyo, L., & Pandey, R. (2001). Theoretical explanation of the uniform compressibility behavior observed in oxide spinels. Physical Review B, 63(18). doi:10.1103/physrevb.63.184101Schulze, G. E. R. (1933). Die Kristallstruktur von BPO4 und BAsO4. Die Naturwissenschaften, 21(30), 562-562. doi:10.1007/bf01503856Scott, H. P., Williams, Q., & Knittle, E. (2001). Ultralow Compressibility Silicate without Highly Coordinated Silicon. Physical Review Letters, 88(1). doi:10.1103/physrevlett.88.015506Shannon, R. D. (1976). Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallographica Section A, 32(5), 751-767. doi:10.1107/s0567739476001551Stubican, V. S., & Roy, R. (1963). High-pressure scheelite-structure polymorphs of rare-earth vanadates and arsenates. Zeitschrift für Kristallographie, 119(1-2), 90-97. doi:10.1524/zkri.1963.119.1-2.90Vinet, P., Ferrante, J., Smith, J. R. & Rose, J. H. (1986). J. Phys. C: Solid State Phys. L, 19, 467.Vorres, K. S. (1962). Correlating ABO4 compound structures. Journal of Chemical Education, 39(11), 566. doi:10.1021/ed039p566Yang, W., Parr, R. G., & Uytterhoeven, L. (1987). New relation between hardness and compressibility of minerals. Physics and Chemistry of Minerals, 15(2), 191-195. doi:10.1007/bf00308783Zhang, J., Song, L., Sist, M., Tolborg, K., & Iversen, B. B. (2018). Chemical bonding origin of the unexpected isotropic physical properties in thermoelectric Mg3Sb2 and related materials. Nature Communications, 9(1). doi:10.1038/s41467-018-06980-

Neutron irradiation defects in gallium sulfide : Optical absorption measurements

Gallium sulfide single crystals have been irradiated with different thermal neutron doses. Defects introduced by neutron irradiation turn out to be optically active, giving rise to absorption bands with energies ranging from 1.2 to 3.2 eV. Bands lying in the band-gap exhibit Gaussian shape. Their energies and widths are independent of the irradiation dose, but their intensities are proportional to it. Thermal annealing is completed in two stages, ending at around 500 and 720 K, respectively. Centers responsible for the absorption bands are proposed to be gallium-vacancy-galliuminterstitial complexes in which the distance between the vacancy (acceptor) and the interstitial (donor) determines the energy and intensity of the absorption band, as well as the annealing [email protected]

Post-spinel transformations and equation of state in ZnGa2O4: Determination at high-pressure by in situ x-ray diffraction

Room temperature angle-dispersive x-ray diffraction measurements on spinel ZnGa2O4 up to 56 GPa show evidence of two structural phase transformations. At 31.2 GPa, ZnGa2O4 undergoes a transition from the cubic spinel structure to a tetragonal spinel structure similar to that of ZnMn2O4. At 55 GPa, a second transition to the orthorhombic marokite structure (CaMn2O4-type) takes place. The equation of state of cubic spinel ZnGa2O4 is determined: V0 = 580.1(9) A3, B0 = 233(8) GPa, B0'= 8.3(4), and B0''= -0.1145 GPa-1 (implied value); showing that ZnGa2O4 is one of the less compressible spinels studied to date. For the tetragonal structure an equation of state is also determined: V0 = 257.8(9) A3, B0 = 257(11) GPa, B0'= 7.5(6), and B0''= -0.0764 GPa-1 (implied value). The reported structural sequence coincides with that found in NiMn2O4 and MgMn2O4.Comment: 20 pages, 4 figures, 2 Table

New high-pressure phase and equation of state of Ce2Zr2O8

In this paper we report a new high-pressure rhombohedral phase of Ce2Zr2O8 observed from high-pressure angle-dispersive x-ray diffraction and Raman spectroscopy studies up to nearly 12 GPa. The ambient-pressure cubic phase of Ce2Zr2O8 transforms to a rhombohedral structure beyond 5 GPa with a feeble distortion in the lattice. Pressure evolution of unit-cell volume showed a change in compressibility above 5 GPa. The unit-cell parameters of the high-pressure rhombohedral phase at 12.1 GPa are ah = 14.6791(3) {\AA}, ch = 17.9421(5) {\AA}, V = 3348.1(1) {\AA}3. The structure relation between the parent cubic (P2_13) and rhombohedral (P3_2) phases were obtained by group-subgroup relations. All the Raman modes of the cubic phase showed linear evolution with pressure with the hardest one at 197 cm-1. Some Raman modes of the high-pressure phase have a non-linear evolution with pressure and softening of one low-frequency mode with pressure is found. The compressibility, equation of state, and pressure coefficients of Raman modes of Ce2Zr2O8 are also reported.Comment: 33 pages, 8 figures, 6 table

Effects of high-pressure on the structural, vibrational, and electronic properties of monazite-type PbCrO4

We have performed an experimental study of the crystal structure, lattice-dynamics, and optical properties of PbCrO4 (the mineral crocoite) at ambient and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band-gap have been accurately determined. X-ray-diffraction, Raman, and optical-absorption experiments have allowed us also to completely characterize two pressure-induced structural phase transitions. The first transition is isostructural, maintaining the monoclinic symmetry of the crystal, and having important consequences in the physical properties; among other a band-gap collapse is induced. The second one involves an increase of the symmetry of the crystal, a volume collapse, and probably the metallization of PbCrO4. The results are discussed in comparison with related compounds and the effects of pressure in the electronic structure explained. Finally, the room-temperature equation of state of the low-pressure phases is also obtained.Comment: 32 pages, 9 figures, 3 table

Zircon to monazite phase transition in CeVO4

X-ray diffraction and Raman-scattering measurements on cerium vanadate have been performed up to 12 and 16 GPa, respectively. Experiments reveal that at 5.3 GPa the onset of a pressure-induced irreversible phase transition from the zircon to the monazite structure. Beyond this pressure, diffraction peaks and Raman-active modes of the monazite phase are measured. The zircon to monazite transition in CeVO4 is distinctive among the other rare-earth orthovanadates. We also observed softening of external translational Eg and internal B2g bending modes. We attributed it to mechanical instabilities of zircon phase against the pressure-induced distortion. We additionally report lattice-dynamical and total-energy calculations which are in agreement with the experimental results. Finally, the effect of non-hydrostatic stresses on the structural sequence is studied and the equations of state of different phases are reported.Comment: 45 pages, 8 figures, 8 table

The evolution of H{\sc ii} galaxies: Testing the bursting scenario through the use of self-consistent models

We have computed a series of realistic and self-consistent models of the emitted spectra of H{\sc ii} galaxies. Our models combine different codes of chemical evolution, evolutionary population synthesis and photoionization. The emitted spectrum of H{\sc ii} galaxies is reproduced by means of the photoionization code CLOUDY, using as ionizing spectrum the spectral energy distribution of the modelled H{\sc ii} galaxy, which in turn is calculated according to a Star Formation History (SFH) and a metallicity evolution given by a chemical evolution model that follows the abundances of 15 different elements. The contribution of emission lines to the broad-band colours is explicitly taken into account. The results of our code are compared with photometric and spectroscopic data of H{\sc ii} galaxies. Our technique reproduces observed diagnostic diagrams, abundances, equivalent width-colour and equivalent width-metallicity relations for local H{\sc ii} galaxies.Comment: 13 figures and 2 tables, accepted for publication in MNRAS Main Journa

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