Pressure-induced ferroelectric to paraelectric transition in LiTaO3 and (Li,Mg)TaO3
- Carnegie Institution of Washington, Washington, DC (United States)
- Osaka Univ., Osaka (Japan)
- Carnegie Institution of Washington, Washington, DC (United States); Center for High Pressure Science and Technology, Shanghai (China)
X-ray powder diffraction and Raman scattering of LiTaO3 (LT) and (Li,Mg)TaO3 (LMT) have been measured under pressure up to 46 GPa. Above 30 GPa, the ferroelectric rhombohedral phase (R3c, Z – 6) of LiTaO3 transforms to a paraelectric orthorhombic phase (Pnma with Z – 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 |Fobs(hkl)| - |Fcal(hkl)| maps of LiTaO3 and (Li,Mg)TaO3 indicate polarization in the c axis direction and a more distinct electron density distribution around the Ta position for (Li,Mg)TaO3 compared to LiTaO3. The observed effective charges indicate that for (Li,Mg)TaO3 without vacancies Ta5+ becomes less ionized as a function of Mg substitution. Considering both site occupancy and effective charge analysis, Ta5+ is reduced to Ta4.13+. Mg2+ and O2- change to Mg1.643+ and O1.732 -, 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)TaO3 indicates more electrons around the Ta site, as confirmed by the effective charge analysis. Raman spectra of LiTaO3 and (Li,Mg)TaO3 show notable changes over the measured pressure range. Raman peaks centered at 250 cm–1 and 350 cm–1 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. Finally, 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.
- Research Organization:
- Carnegie Inst. of Washington, Washington, DC (United States); Energy Frontier Research Centers (EFRC) (United States). Energy Frontier Research in Extreme Environments (EFree)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- NA0002006; AC02-06CH11357; FG02-99ER45775; NA-0002006; NA0001974; SC-0001057
- OSTI ID:
- 1338347
- Alternate ID(s):
- OSTI ID: 1238078
- Journal Information:
- Journal of Applied Physics, Vol. 119, Issue 7; ISSN 0021-8979
- Publisher:
- American Institute of Physics (AIP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Pressure-induced transformations of multiferroic relaxor PbFe 0.5 Nb 0.5 O 3
|
journal | February 2018 |
Three dimensional phase-field simulations on the frequency dependence of polarization vectors and hysteresis loops in ferroelectric crystals
|
journal | February 2019 |
Similar Records
Crystallization behavior of Li{sub 1{minus}5{ital x}}Ta{sub 1+{ital x}}O{sub 3} glasses synthesized from liquid precursors
Synthesis, crystal structures and photoluminescence properties of new oxyborates, Mg{sub 5}NbO{sub 3}(BO{sub 3}){sub 3} and Mg{sub 5}TaO{sub 3}(BO{sub 3}){sub 3}, with novel warwickite-type superstructures