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Title: Crystal Stability and Pressure-Induced Phase Transitions in Scheelite AWO4(A=Ca,Sr,Ba,Pb,Eu) Binary Oxides. I: A Review of Recent ab initio Calculations, ADXRD, XANES, and Raman Studies

Abstract

The structural properties of CaWO{sub 4}, SrWO{sub 4}, BaWO{sub 4}, PbWO{sub 4}, and EuWO{sub 4} scintillating crystals under pressure have been studied by X-ray powder diffraction, X-ray absorption near-edge structure measurements, Raman spectroscopy, and ab initio density functional theory calculations. The results obtained from these studies will be reviewed here and their differences and similitudes discussed.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930411
Report Number(s):
BNL-81143-2008-JA
Journal ID: ISSN 0370-1972; PSSBBD; TRN: US200904%%690
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physica Status Solidi B; Journal Volume: 244; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ABSORPTION; CALCIUM TUNGSTATES; CRYSTAL STRUCTURE; CRYSTALS; DIFFRACTION; FUNCTIONALS; OXIDES; RAMAN SPECTROSCOPY; STABILITY; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Lopez-Solano,J., Rodriguez-Hernandez, P., Radescu, S., Mujica, A., Munoz, A., Errandonea, D., Manjon, F., Pellicer-Porres, J., Garro, N., and et al.. Crystal Stability and Pressure-Induced Phase Transitions in Scheelite AWO4(A=Ca,Sr,Ba,Pb,Eu) Binary Oxides. I: A Review of Recent ab initio Calculations, ADXRD, XANES, and Raman Studies. United States: N. p., 2007. Web. doi:10.1002/pssb.200672559.
Lopez-Solano,J., Rodriguez-Hernandez, P., Radescu, S., Mujica, A., Munoz, A., Errandonea, D., Manjon, F., Pellicer-Porres, J., Garro, N., & et al.. Crystal Stability and Pressure-Induced Phase Transitions in Scheelite AWO4(A=Ca,Sr,Ba,Pb,Eu) Binary Oxides. I: A Review of Recent ab initio Calculations, ADXRD, XANES, and Raman Studies. United States. doi:10.1002/pssb.200672559.
Lopez-Solano,J., Rodriguez-Hernandez, P., Radescu, S., Mujica, A., Munoz, A., Errandonea, D., Manjon, F., Pellicer-Porres, J., Garro, N., and et al.. Mon . "Crystal Stability and Pressure-Induced Phase Transitions in Scheelite AWO4(A=Ca,Sr,Ba,Pb,Eu) Binary Oxides. I: A Review of Recent ab initio Calculations, ADXRD, XANES, and Raman Studies". United States. doi:10.1002/pssb.200672559.
@article{osti_930411,
title = {Crystal Stability and Pressure-Induced Phase Transitions in Scheelite AWO4(A=Ca,Sr,Ba,Pb,Eu) Binary Oxides. I: A Review of Recent ab initio Calculations, ADXRD, XANES, and Raman Studies},
author = {Lopez-Solano,J. and Rodriguez-Hernandez, P. and Radescu, S. and Mujica, A. and Munoz, A. and Errandonea, D. and Manjon, F. and Pellicer-Porres, J. and Garro, N. and et al.},
abstractNote = {The structural properties of CaWO{sub 4}, SrWO{sub 4}, BaWO{sub 4}, PbWO{sub 4}, and EuWO{sub 4} scintillating crystals under pressure have been studied by X-ray powder diffraction, X-ray absorption near-edge structure measurements, Raman spectroscopy, and ab initio density functional theory calculations. The results obtained from these studies will be reviewed here and their differences and similitudes discussed.},
doi = {10.1002/pssb.200672559},
journal = {Physica Status Solidi B},
number = 1,
volume = 244,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The equilibrium geometries of the metallocenes MCp{sub 2}(M = Ca, Sr, Ba, Sm, Eu, or Yb) have been studied by ab initio pseudopotential calculations at the Hartree-Fock (HF), MP2, and CISD levels. In the HF calculations all molecules are found to favor regular ({open_quotes}linear{close_quotes}) sandwich-type equilibrium structures with increasingly shallow potential energy surfaces for the bending motions along the series M = Ca, Yb, Sr, Eu, Sm, and Ba. Large-scale MP2 calculations for BaCp{sub 2} yield a (ring centroid)-Ba-(ring centroid) angle of ca. 147{degrees}. However, the linearization energy is less than 1.5 kJ/mol. Thus, barocene can be described as amore » {open_quotes}quasilinear{close_quotes} molecule. The same description seems appropriate for samarocene and europocene. However, CaCp{sub 2} and probably YbCp{sub 2} are genuinely linear, whereas SrCp{sub 2} is intermediate. The low bending potentials of all species studied (even CaCp{sub 2}) permit large-amplitude bending motions. Hence, our computational results for these floppy organometallics can be reconciled with the experimentally observed, bent, thermal average, gas-phase structures of the permethylated metallocenes MCp*{sub 2}(M = Ca, Sr, Ba, or Yb; Cp* = {eta}{sub 5}C{sub 5}Me{sub 5}). As is indicated by natural population analysis (NPA), the largely {pi}-type covalent contributions to M-Cp bonding are responsible for the considerably smaller preference for bent structures compared with. e.g., the corresponding dihalides (MX{sub 2}) or dimethyl compounds (MMe{sub 2}) 37 refs., 2 figs., 6 tabs.« less
  • This work reports high pressure Raman scattering results on dipotassium molybdate (K{sub 2}MoO{sub 4}). The effects of hydrostatic pressure on the vibrational properties of K{sub 2}MoO{sub 4} has been investigated in the pressure range from 0.5 to 7.3 GPa. This study also indicates that K{sub 2}MoO{sub 4} crystals exhibit a pressure-induced first-order phase transition at about 2.2 GPa from monoclinic to an unknown symmetry. Calculaions based on density-functional theory (DFT) unveiled the structural changes undergone by the K{sub 2}MoO{sub 4} system under hydrostatic pressure. The phase transition is connected with the increase of the polyhedral KO{sub 6} distortion due tomore » an increased anionic interaction as volume decrease, therefore leading to tiltings and/or rotations of the MoO{sub 4} tetrahedra. The consequence of such tiltings and/or rotations of the MoO{sub 4} tetrahedra is to increase the disorder of these units. The high-pressure phase transforms directly into the ambient-pressure phase as pressure is released. - Graphical Abstract: Dipotassium molybdate (K{sub 2}MoO{sub 4}) belongs to the class of single molybdates and tungstates with a general composition of the A{sub 2}MO{sub 4} (A=Li, Na, K, Rb, Cs; {Mu}=Mo, W). At room temperature and ambient pressure, the crystal of K{sub 2}MoO{sub 4} is monoclinic and it belongs to the C2/m (C{sub 2h}{sup 3}) space group. This material is attracting a considerable attention due to its interesting structural and thermodynamic properties. This work reports a high pressure study on this system. Highlights: Black-Right-Pointing-Pointer We reports high pressure Raman scattering results on dipotassium molybdate. Black-Right-Pointing-Pointer Our study indicates a pressure-induced first-order phase transition at around 2.16 GPa. Black-Right-Pointing-Pointer DFT calculations indicate that phase transition is connected with the increase of KO{sub 6} distortion. Black-Right-Pointing-Pointer Tiltings and/or rotations of the MoO{sub 4} tetrahedra are related to increased disorder.« less
  • We report on pseudopotential calculations of the structural properties and pressure-induced solid-solid phase transitions for four II-VI compounds: ZnSe, ZnTe, CdSe, and CdTe. For each of these compounds, we fix the zinc-blende structure as the ambient pressure phase and consider the rocksalt, cinnabar, and Cmcm structures as candidates for the high-pressure phases. We calculate the transition pressures and the changes in specific volume for each compound. The pressure dependences of the structural parameters of the cinnabar and the Cmcm phases are determined. The Cmcm structure appears to be a common high-pressure phase for the II-VI and III-V semiconductors. {copyright} {italmore » 1997} {ital The American Physical Society}« less
  • High-pressure Raman scattering and optical absorption studies have been carried out on lead pyroniobate (Pb{sub 2}Nb{sub 2}O{sub 7}) up to 33 GPa, using a gasketed diamond anvil cell. The Raman study reveals the occurrence of two, possibly three, pressure-induced phase changes; a rather subtle change is indicated near 4.5 GPa. The transition near 13 GPa is attributed to a structural transition from the rhombohedral to the cubic pyrochlore structure. The third phase change occurs near 20 GPa. From the broad Raman feature that is observed at about 800 cm{sup {minus}1}, it is concluded that the system turns amorphous at pressuresmore » above 20 GPa. The amorphous phase recrystallizes to the original rhombohedral phase, on release of pressure. The broad Raman peaks of the recrystallized phase indicate a high degree of disorder in the material. Lead pyroniobate turns deep red near 30 GPa, from light yellow at ambient pressure. Semi quantitative absorption measurements show that the energy gap shifts red at a rate of 30 meV/GPa. This shift is attributed to the downward motion of the 5d (es) conduction band of Pb.« less
  • Here, we describe how first principle calculations can play a key role in the interpretation of X-ray absorption near-edge structure (XANES) and X-ray magnetic circular dichroism (XMCD) spectra for a better understanding of emergent phenomena in condensed matter physics at high applied pressure. Eu compounds are used as case study to illustrate the advantages of this methodology, ranging from studies of electronic charge transfer probed by quadrupolar and dipolar contributions, to accurately determining electronic valence, and to inform about the influence of pressure on RKKY interactions and magnetism. This description should help advance studies where the pressure dependence of XANESmore » and XMCD data must be tackled with the support of theoretical calculations for a proper understanding of the electronic properties of materials.« less