Charge density analysis of SiO<sub>2</sub>under pressures over 50 GPa using a new diamond anvil cell for single-crystal structure analysis

Yamanaka, T.; Fukuda, Tomoo; Komatsu, Yutaka; Sumiya, Hitoshi

doi:10.1088/0953-8984/14/44/330

Cited by 9 publications

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References 11 publications

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“…Detailed discussion of the derivation of the core f core and f valence have been described previously. 27 Under ambient conditions, P j,valence and j-parameter are observed from the structure refinement. P Ta,valence , P Mg,valence , O a,valence , j Ta , j Mg , and j O of Ta and Mg are variable parameters in the calculation.…”

Section: A Ta Effective Charges In (Limg)taomentioning

confidence: 99%

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Yamanaka

Nakamoto

Takei

et al. 2016

Journal of Applied Physics

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X-ray powder diffraction and Raman scattering of LiTaO 3 (LT) and (Li,Mg)TaO 3 (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z ¼ 6) of LiTaO 3 transforms to a paraelectric orthorhombic phase (Pnma with Z ¼ 4) with a large hysteresis. Rietveld profile fitting analysis shows that the Li-O bond is compressed and approaches that of Ta-O with pressure. The cation distribution analysis of the orthorhombic perovskite structure shows that Li and Ta are located in the octahedral 8-fold coordination sites. Difference Fourier jF obs (hkl)j-jF cal (hkl)j maps of LiTaO 3 and (Li,Mg)TaO 3 indicate polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO 3 compared to LiTaO 3. The observed effective charges indicate that for (Li,Mg)TaO 3 without vacancies Ta 5þ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta 5þ is reduced to Ta 4.13þ. Mg 2þ and O 2change to Mg 1.643þ and O 1.732-, respectively. The space-and time-averaged structures of the dynamical vibration of atoms can be elucidated from the electron density analysis by difference Fourier and temperature factors T(hkl) in the structure refinement. The refinement of the temperature factor is consistent with the cation distribution assuming full stoichiometry. The residual electron density induced from the excess electron in (Li,Mg)TaO 3 indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO 3 and (Li,Mg)TaO 3 show notable changes over the measured pressure range. Raman peaks centered at 250 cm À1 and 350 cm À1 at ambient pressure merge above 8 GPa, which we associate with the diminishing of difference in distances between Li-O and Ta-O bonds with pressure in both materials. Raman spectra show significant changes at 28 GPa and 33 GPa for LT and LMT, respectively, due to the structural transition from R3c to Pnma consistent with the x-ray diffraction results. V

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Section: A Ta Effective Charges In (Limg)taomentioning

confidence: 99%

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Yamanaka

Nakamoto

Takei

et al. 2016

Journal of Applied Physics

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Theoretical modeling of the Al paramagnetic center and its precursors in stishovite

Botis

Pan

2009

Phys Chem Minerals

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High-pressure structure determination and refinement by X-ray diffraction

Angel¹

2005

Advances in High-Pressure Technology for Geophysical Applications

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Charge density analysis of SiO₂under pressures over 50 GPa using a new diamond anvil cell for single-crystal structure analysis

Cited by 9 publications

References 11 publications

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Theoretical modeling of the Al paramagnetic center and its precursors in stishovite

High-pressure structure determination and refinement by X-ray diffraction

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Charge density analysis of SiO2under pressures over 50 GPa using a new diamond anvil cell for single-crystal structure analysis

Cited by 9 publications

References 11 publications

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3

Theoretical modeling of the Al paramagnetic center and its precursors in stishovite

High-pressure structure determination and refinement by X-ray diffraction

Contact Info

Product

Resources

About

Charge density analysis of SiO₂under pressures over 50 GPa using a new diamond anvil cell for single-crystal structure analysis