57 research outputs found
Optical absorption of divalent metal tungstates: Correlation between the band-gap energy and the cation ionic radius
We have carried out optical-absorption and reflectance measurements at room
temperature in single crystals of AWO4 tungstates (A = Ba, Ca, Cd, Cu, Pb, Sr,
and Zn). From the experimental results their band-gap energy has been
determined to be 5.26 eV (BaWO4), 5.08 eV (SrWO4), 4.94 eV (CaWO4), 4.15 eV
(CdWO4), 3.9-4.4 eV (ZnWO4), 3.8-4.2 eV (PbWO4), and 2.3 eV (CuWO4). The
results are discussed in terms of the electronic structure of the studied
tungstates. It has been found that those compounds where only the s electron
states of the A2+ cation hybridize with the O 2p and W 5d states (e.g BaWO4)
have larger band-gap energies than those where also p, d, and f states of the
A2+ cation contribute to the top of the valence band and the bottom of the
conduction band (e.g. PbWO4). The results are of importance in view of the
large discrepancies existent in prevoiusly published data.Comment: 16 pages, 3 figures, 1 tabl
High-pressure structural investigation of several zircon-type orthovanadates
Room temperature angle-dispersive x-ray diffraction measurements on
zircon-type EuVO4, LuVO4, and ScVO4 were performed up to 27 GPa. In the three
compounds we found evidence of a pressure-induced structural phase
transformation from zircon to a scheelite-type structure. The onset of the
transition is near 8 GPa, but the transition is sluggish and the low- and
high-pressure phases coexist in a pressure range of about 10 GPa. In EuVO4 and
LuVO4 a second transition to a M-fergusonite-type phase was found near 21 GPa.
The equations of state for the zircon and scheelite phases are also determined.
Among the three studied compounds, we found that ScVO4 is less compressible
than EuVO4 and LuVO4, being the most incompressible orthovanadate studied to
date. The sequence of structural transitions and compressibilities are
discussed in comparison with other zircon-type oxides.Comment: 34 pages, 2 Tables, 11 Figure
High-pressure stability and compressibility of APO4 (A = La, Nd, Eu, Gd, Er, and Y) orthoposphates: A synchrotron powder x-ray diffraction study
Room temperature angle-dispersive x-ray diffraction measurements on
zircon-type YPO4 and ErPO4, and monazite-type GdPO4, EuPO4, NdPO4, and LaPO4
were performed in a diamond-anvil cell up to 27 GPa using neon as
pressure-transmitting medium. In the zircon-structured oxides we found evidence
of a reversible pressure-induced structural phase transformation from zircon to
a monazite-type structure. The onset of the transition is near 17-20 GPa. In
LaPO4 a non-reversible transition is found around 26 GPa, being a barite-type
structure proposed for the high-pressure phase. In the other three monazites,
this structure is found to be stable up to highest pressure reached in the
experiments. No additional phase transitions or evidences of chemical
decomposition are found in the experiments. The equations of state and axial
compressibility for the different phases are also determined. In particular, we
found that in a given compound the monazite structure is less compressible than
zircon structure, being this fact related to the larger packing efficiency of
monazite compared with zircon. The differential bond compressibility of
different polyhedra is also reported and related the anisotropic
compressibility of both structures. Finally, the sequence of structural
transitions and compressibilities are discussed in comparison with other
orhtophosphates.Comment: 38 pages, 10 figures, 2 table
Complex high-pressure polymorphism of barium tungstate
We have studied BaWO 4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO 4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO 4-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure- transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may be responsible for previously reported rich polymorphism in BaWO 4. The crystal structure of the low- and high-pressure phases from the quasihydrostatic experiments has been Rietveld refined. Additionally, for the tetragonal phase the effects of pressure on the unit-cell volume and lattice parameters are discussed. Finally, the pressure evolution of the Raman modes of different phases is reported and compared with previous studies. © 2012 American Physical Society.This research was supported by Spanish MEC (Grant No. MAT2010-21270-C04-01/04), MALTA Consolider Ingenio 2010 (Grant No. CSD2007-00045), and Vicerrectorado de Investigacion y Desarrollo of the Universitat Politecnica de Valencia (Grants No. UPV2011-0914 PAID-05-11 and No. UPV2011-0966 PAID-06-11). XRD data were collected at HPCAT, Advanced Photon Source (APS), Argonne National Laboratory. HPCAT is supported by CIW, CDAC, UNLV, and LLNL through funding from DOE-NNSA, DOE-BES, and NSF. APS is supported by DOE-BES under Contract No. DEAC02-06CH11357.Gomis Hilario, O.; Sans, JA.; Lacomba-Perales, R.; Errandonea, D.; Meng, Y.; Chervin, JC.; Polian, A. (2012). Complex high-pressure polymorphism of barium tungstate. Physical Review B. 86:54121-1-54121-10. https://doi.org/10.1103/PhysRevB.86.054121S54121-154121-1086Gürmen, E., Daniels, E., & King, J. S. (1971). Crystal Structure Refinement of SrMoO4, SrWO4, CaMoO4, and BaWO4 by Neutron Diffraction. The Journal of Chemical Physics, 55(3), 1093-1097. doi:10.1063/1.1676191Errandonea, 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.2008.02.001Tan, D., Xiao, W., Zhou, W., Chen, M., Zhou, W., Li, X., … Liu, J. (2012). High pressure X-ray diffraction study on BaWO4-II. High Pressure Research, 1-8. doi:10.1080/08957959.2012.658789Lacomba-Perales, R., Errandonea, D., Segura, A., Ruiz-Fuertes, J., Rodríguez-Hernández, P., Radescu, S., … Muñoz, A. (2011). A combined high-pressure experimental and theoretical study of the electronic band-structure of scheelite-type AWO4 (A = Ca, Sr, Ba, Pb) compounds. Journal of Applied Physics, 110(4), 043703. doi:10.1063/1.3622322Lacomba-Perales, R., Martinez-García, D., Errandonea, D., Le Godec, Y., Philippe, J., Le Marchand, G., … López-Solano, J. (2010). Experimental and theoretical investigation of the stability of the monoclinicBaWO4-II phase at high pressure and high temperature. Physical Review B, 81(14). doi:10.1103/physrevb.81.144117Da-Yong, T., Wan-Sheng, X., Wen-Ge, Z., Mao-Shuang, S., Xiao-Lin, X., & Ming, C. (2009). Raman Investigation of BaWO4-II Phase under Hydrostatic Pressures up to 14.8 GPa. Chinese Physics Letters, 26(4), 046301. doi:10.1088/0256-307x/26/4/046301Manjón, F. J., Errandonea, D., Garro, N., Pellicer-Porres, J., Rodríguez-Hernández, P., Radescu, S., … Muñoz, A. (2006). Lattice dynamics study of scheelite tungstates under high pressure I.BaWO4. Physical Review B, 74(14). doi:10.1103/physrevb.74.144111Grzechnik, A., Crichton, W. A., Marshall, W. G., & Friese, K. (2006). High-pressure x-ray and neutron powder diffraction study of PbWO4and BaWO4scheelites. Journal of Physics: Condensed Matter, 18(11), 3017-3029. doi:10.1088/0953-8984/18/11/008Errandonea, D., Pellicer-Porres, J., Manjón, F. J., Segura, A., Ferrer-Roca, C., Kumar, R. S., … Aquilanti, G. (2006). Determination of the high-pressure crystal structure ofBaWO4andPbWO4. Physical Review B, 73(22). doi:10.1103/physrevb.73.224103Panchal, V., Garg, N., Chauhan, A. K., Sangeeta, & Sharma, S. M. (2004). High pressure phase transitions in BaWO4. Solid State Communications, 130(3-4), 203-208. doi:10.1016/j.ssc.2004.01.043Jayaraman, A., Batlogg, B., & VanUitert, L. G. (1983). High-pressure Raman study of alkaline-earth tungstates and a new pressure-induced phase transition in BaWO4. Physical Review B, 28(8), 4774-4777. doi:10.1103/physrevb.28.4774Kawada, I., Kato, K., & Fujita, T. (1974). BaWO4-II (a high-pressure form). Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 30(8), 2069-2071. doi:10.1107/s0567740874006431Fujita, T., Yamaoka, S., & Fukunaga, O. (1974). Pressure induced phase transformation in BaWO4. Materials Research Bulletin, 9(2), 141-146. doi:10.1016/0025-5408(74)90193-7Manjon, F. J., Errandonea, D., Garro, N., Pellicer-Porres, J., López-Solano, J., Rodríguez-Hernández, P., … Muñoz, A. (2006). Lattice dynamics study of scheelite tungstates under high pressure II.PbWO4. Physical Review B, 74(14). doi:10.1103/physrevb.74.144112Errandonea, D., Martínez-García, D., Lacomba-Perales, R., Ruiz-Fuertes, J., & Segura, A. (2006). Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals. Applied Physics Letters, 89(9), 091913. doi:10.1063/1.2345228Mao, H. K., Xu, J., & Bell, P. M. (1986). Calibration of the ruby pressure gauge to 800 kbar under quasi-hydrostatic conditions. Journal of Geophysical Research, 91(B5), 4673. doi:10.1029/jb091ib05p04673Klotz, S., Chervin, J.-C., Munsch, P., & Le Marchand, G. (2009). Hydrostatic limits of 11 pressure transmitting media. Journal of Physics D: Applied Physics, 42(7), 075413. doi:10.1088/0022-3727/42/7/075413Hammersley, A. P., Svensson, S. O., Hanfland, M., Fitch, A. N., & Hausermann, D. (1996). Two-dimensional detector software: From real detector to idealised image or two-theta scan. High Pressure Research, 14(4-6), 235-248. doi:10.1080/08957959608201408Holland, T. J. B., & Redfern, S. A. T. (1997). Unit cell refinement from powder diffraction data: the use of regression diagnostics. Mineralogical Magazine, 61(404), 65-77. doi:10.1180/minmag.1997.061.404.07Toby, B. H. (2001). EXPGUI, a graphical user interface forGSAS. Journal of Applied Crystallography, 34(2), 210-213. doi:10.1107/s0021889801002242Kraus, W., & Nolze, G. (1996). POWDER CELL – a program for the representation and manipulation of crystal structures and calculation of the resulting X-ray powder patterns. Journal of Applied Crystallography, 29(3), 301-303. doi:10.1107/s0021889895014920Birch, F. (1978). Finite strain isotherm and velocities for single-crystal and polycrystalline NaCl at high pressures and 300°K. Journal of Geophysical Research, 83(B3), 1257. doi:10.1029/jb083ib03p01257Liu, H., Ding, Y., Somayazulu, M., Qian, J., Shu, J., Häusermann, D., & Mao, H. (2005). Rietveld refinement study of the pressure dependence of the internal structural parameteruin the wurtzite phase of ZnO. Physical Review B, 71(21). doi:10.1103/physrevb.71.212103Liu, H., Hu, J., Shu, J., Häusermann, D., & Mao, H. (2004). Lack of the critical pressure for weakening of size-induced stiffness in 3C–SiC nanocrystals under hydrostatic compression. Applied Physics Letters, 85(11), 1973-1975. doi:10.1063/1.1789240Ruiz-Fuertes, J., Errandonea, D., Lacomba-Perales, R., Segura, A., González, J., Rodríguez, F., … Tu, C. Y. (2010). High-pressure structural phase transitions inCuWO4. Physical Review B, 81(22). doi:10.1103/physrevb.81.224115Santamaría-Pérez, D., Gracia, L., Garbarino, G., Beltrán, A., Chuliá-Jordán, R., Gomis, O., … Segura, A. (2011). High-pressure study of the behavior of mineral barite by x-ray diffraction. Physical Review B, 84(5). doi:10.1103/physrevb.84.054102Finger, L. W., Kroeker, M., & Toby, B. H. (2007). DRAWxtl, an open-source computer program to produce crystal structure drawings. Journal of Applied Crystallography, 40(1), 188-192. doi:10.1107/s0021889806051557Achary, S. N., Patwe, S. J., Mathews, M. D., & Tyagi, A. K. (2006). High temperature crystal chemistry and thermal expansion of synthetic powellite (CaMoO4): A high temperature X-ray diffraction (HT-XRD) study. Journal of Physics and Chemistry of Solids, 67(4), 774-781. doi:10.1016/j.jpcs.2005.11.009Machon, D., Dmitriev, V. P., Bouvier, P., Timonin, P. N., Shirokov, V. B., & Weber, H.-P. (2003). Pseudoamorphization ofCs2HgBr4. Physical Review B, 68(14). doi:10.1103/physrevb.68.144104Ruiz-Fuertes, J., Friedrich, A., Pellicer-Porres, J., Errandonea, D., Segura, A., Morgenroth, W., … Polian, A. (2011). Structure Solution of the High-Pressure Phase of CuWO4and Evolution of the Jahn–Teller Distortion. Chemistry of Materials, 23(18), 4220-4226. doi:10.1021/cm201592hErrandonea, 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.2004.10.030Errandonea, D., Kumar, R. S., Ruiz-Fuertes, J., Segura, A., & Haussühl, E. (2011). High-pressure study of substrate material ScAlMgO4. Physical Review B, 83(14). doi:10.1103/physrevb.83.144104Wang, J.-T., Chen, C., & Kawazoe, Y. (2011). Low-Temperature Phase Transformation from Graphite tosp3Orthorhombic Carbon. Physical Review Letters, 106(7). doi:10.1103/physrevlett.106.075501Errandonea, D., & Manjón, F. J. (2009). On the ferroelastic nature of the scheelite-to-fergusonite phase transition in orthotungstates and orthomolybdates. Materials Research Bulletin, 44(4), 807-811. doi:10.1016/j.materresbull.2008.09.024Maczka, M., Souza Filho, A. G., Paraguassu, W., Freire, P. T. C., Mendes Filho, J., & Hanuza, J. (2012). Pressure-induced structural phase transitions and amorphization in selected molybdates and tungstates. Progress in Materials Science, 57(7), 1335-1381. doi:10.1016/j.pmatsci.2012.01.001Flórez, M., Contreras-García, J., Recio, J. M., & Marqués, M. (2009). Quantum-mechanical calculations of zircon to scheelite transition pathways inZrSiO4. Physical Review B, 79(10). doi:10.1103/physrevb.79.104101Errandonea, D., Gracia, L., Beltrán, A., Vegas, A., & Meng, Y. (2011). Pressure-induced phase transitions in AgClO4. Physical Review B, 84(6). doi:10.1103/physrevb.84.06410
A combined high-pressure experimental and theoretical study of the electronic band-structure of scheelite-type AWO4 (A = Ca, Sr, Ba, Pb) compounds
The optical-absorption edge of single crystals of CaWO4, SrWO4, BaWO4, and
PbWO4 has been measured under high pressure up to ~20 GPa at room temperature.
From the measurements we have obtained the evolution of the band-gap energy
with pressure. We found a low-pressure range (up to 7-10 GPa) where
alkaline-earth tungstates present a very small Eg pressure dependence (-2.1 <
dEg/dP < 8.9 meV/GPa). In contrast, in the same pressure range, PbWO4 has a
pressure coefficient of -62 meV/GPa. The high-pressure range is characterized
in the four compounds by an abrupt decrease of Eg followed by changes in
dEg/dP. The band-gap collapse is larger than 1.2 eV in BaWO4. We also
calculated the electronic-band structures and their pressure evolution.
Calculations allow us to interpret experiments considering the different
electronic configuration of divalent metals. Changes in the pressure evolution
of Eg are correlated with the occurrence of pressure-induced phase transitions.
The band structures for the low- and high-pressure phases are also reported. No
metallization of any of the compounds is detected in experiments nor is
predicted by calculations.Comment: 26 pages, 1 table, 6 figure
Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals
The pressure behavior of the absorption edge of PbWO4 was studied up to 15.3
GPa. It red-shifts at -71 meV/GPa below 6.1 GPa, but at 6.3 GPa the band-gap
collapses from 3.5 eV to 2.75 eV. From 6.3 GPa to 11.1 GPa, the absorption edge
moves with a pressure coefficient of -98 meV/GPa, undergoing additional changes
at 12.2 GPa. The results are discussed in terms of the electronic structure of
PbWO4 which attribute the behavior of the band-gap to changes in the local
atomic structure. The changes observed at 6.3 GPa and 12.2 GPa are attributed
to phase transitions.Comment: 14 pages, 3 figure
High-pressure phase transitions and compressibility of wolframite-type tungstates
This paper reports an investigation on the phase diagram and compressibility of wolframite-type tungstates by means of x-ray powder diffraction and absorption in a diamond-anvil cell and ab initio calculations. X-ray diffraction experiments show that monoclinic wolframite-type MgWO4 suffers at least two phase transitions, the first one being to a triclinic polymorph with a structure similar to that of CuWO4 and FeMoO4-II. The onset of each transition is detected at 17.1 and 31 GPa. In ZnWO4 the onset of the monoclinic-triclinic transition has been also found at 16.7 GPa. This transition does not involve any change in the atomic coordination as confirmed by x-ray absorption measurements. These findings are supported by density-functional theory calculations, which predict the occurrence of additional transitions upon further compression. Calculations have been also performed for wolframite-type MnWO4, which is found to have an antiferromagnetic configuration. In addition, our study reveals details of the local-atomic compression in MgWO4 and ZnWO4. In particular, below the transition pressure the ZnO6 and equivalent polyhedra tend to become more regular, whereas, the WO6 octahedra remain almost unchanged. Fitting the pressure-volume data we obtained the equation of state for the low-pressure phase of MgWO4 and ZnWO4. These and previous results on MnWO4 and CdWO4 are compared with the calculations. The compressibility of wolframite-type tungstates is also systematically discussed. Finally Raman spectroscopy measurements and lattice dynamics calculations are presented for MgWO4
High-pressure structural phase transitions in CuWO4
We study the effects of pressure on the structural, vibrational, and magnetic
behavior of cuproscheelite. We performed powder x-ray diffraction and Raman
spectroscopy experiments up to 27 GPa as well as ab initio total-energy and
lattice-dynamics calculations. Experiments provide evidence that a structural
phase transition takes place at 10 GPa from the low-pressure triclinic phase
(P-1) to a monoclinic wolframite-type structure (P2/c). Calculations confirmed
this finding and indicate that the phase transformation involves a change in
the magnetic order. In addition, the equation of state for the triclinic phase
is determined: V0 = 132.8(2) A3, B0 = 139 (6) GPa and = 4. Furthermore,
experiments under different stress conditions show that non-hydrostatic
stresses induce a second phase transition at 17 GPa and reduce the
compressibility of CuWO4, B0 = 171(6) GPa. The pressure dependence of all Raman
modes of the triclinic and high-pressure phases is also reported and discussed.Comment: 33 pages, 9 figures, 5 table
Phase behaviour of Ag2CrO4 under compression: Structural, vibrational, and optical properties
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher.
To access the final edited and published work see http://dx.doi.org/10.1021/jp401524sWe have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of silver chromate (Ag2CrO4) at ambient temperature and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. When the initial orthorhombic Pnma Ag2CrO4 structure (phase I) is compressed up to 4.5 GPa, a previously undetected phase (phase II) has been observed with a 0.95% volume collapse. The structure of phase II can be indexed to a similar orthorhombic cell as phase I, and the transition can be considered to be an isostructural transition. This collapse is mainly due to the drastic contraction of the a axis (1.3%). A second phase transition to phase III occurs at 13 GPa to a structure not yet determined. First-principles calculations have been unable to reproduce the isostructural phase transition, but they propose the stabilization of a spinel-type structure at 11 GPa. This phase is not detected in experiments probably because of the presence of kinetic barriers. Experiments and calculations therefore seem to indicate that a new structural and electronic description is required to model the properties of silver chromate.This study was supported by the Spanish government MEC under grants MAT2010-21270-C04-01/03/04 and CTQ2009-14596-C02-01, by the Comunidad de Madrid and European Social Fund (S2009/PPQ1551 4161893), by the 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). 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 its financial support. Diamond and ALBA Synchrotron Light Sources are acknowledged for provisions of beam time. We also thank Drs. Peral, Popescu, and Fauth for technical support.Santamaría Pérez, D.; Bandiello, E.; Errandonea, D.; Ruiz-Fuertes, J.; Gomis Hilario, O.; Sans, JÁ.; Manjón Herrera, FJ.... (2013). Phase behaviour of Ag2CrO4 under compression: Structural, vibrational, and optical properties. Journal of Physical Chemistry C. 117(23):12239-12248. https://doi.org/10.1021/jp401524sS12239122481172
- …