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Title: Structural Change of Layered Perovskite La2Ti2O7 at High Pressures

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930346
Report Number(s):
BNL-81059-2008-JA
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
national synchrotron light source

Citation Formats

Zhang,F., Lian, J., Becker, U., Ewing, R., Wang, L., Hu, J., and Saxena, S. Structural Change of Layered Perovskite La2Ti2O7 at High Pressures. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2006.11.022.
Zhang,F., Lian, J., Becker, U., Ewing, R., Wang, L., Hu, J., & Saxena, S. Structural Change of Layered Perovskite La2Ti2O7 at High Pressures. United States. doi:10.1016/j.jssc.2006.11.022.
Zhang,F., Lian, J., Becker, U., Ewing, R., Wang, L., Hu, J., and Saxena, S. Mon . "Structural Change of Layered Perovskite La2Ti2O7 at High Pressures". United States. doi:10.1016/j.jssc.2006.11.022.
@article{osti_930346,
title = {Structural Change of Layered Perovskite La2Ti2O7 at High Pressures},
author = {Zhang,F. and Lian, J. and Becker, U. and Ewing, R. and Wang, L. and Hu, J. and Saxena, S.},
abstractNote = {},
doi = {10.1016/j.jssc.2006.11.022},
journal = {Journal of Solid State Chemistry},
number = 2,
volume = 180,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The perovskite-related layered structure of La{sub 2}Ti{sub 2}O{sub 7} has been studied at pressures up to 30 GPa using synchrotron radiation powder X-ray diffraction (XRD) and Raman scattering. The XRD results indicate a pronounced anisotropy for the compressibility of the monoclinic unit cell. The ratio of the relative compressibilities along the [100], [010] and [001] directions is {approx}1:3:5. The greatest compressibility is along the [001] direction, perpendicular to the interlayer. A pressure-induced phase transition occurs at 16.7 GPa. Both Raman and XRD measurements reveal that the pressure-induced phase transition is reversible. The high-pressure phase has a close structural relation tomore » the low-pressure monoclinic phase and the phase transition may be due to the tilting of TiO{sub 6} octahedra at high pressures. - Graphical abstract: La{sub 2}Ti{sub 2}O{sub 7} is a layered perovskite and it shows anisotropic compressibility at high pressures. The in situ XRD and Raman measurements indicate a structural transformation takes place at 16.7 GPa.« less
  • A deuterated n=1 Ruddlesden-Popper compound, DLnTiO{sub 4} (HLnTiO{sub 4}, Ln=La, Nd and Y), was prepared by an ion-exchange reaction of Na{sup +} ions in NaLnTiO{sub 4} with D{sup +} ions, and its structure was analyzed by Rietveld method using powder neutron diffraction data. The structure analyses showed that DLaTiO{sub 4} and DNdTiO{sub 4} crystallized in the space group P4/nmm with a=3.7232(1) and c=12.3088(1)A, and a=3.7039(1) and c=12.0883(1)A, respectively. On the other hand, DYTiO{sub 4} crystallized in the space group P2{sub 1}/c with a=11.460(1), b=5.2920(4), c=5.3628(5)A and {beta}=90.441(9){sup o}. The loaded protons were found to statistically occupy the sites around anmore » apical oxygen of TiO{sub 6} octahedron in the interlayer of these compounds, rather than Na atom sites in NaLnTiO{sub 4}.« less
  • Lattice parameters of a synthetic powder sample of Ca{sub 0.35}Sr{sub 0.65}TiO{sub 3} perovskite have been determined by the method of Le Bail refinement, using synchrotron X-ray diffraction patterns collected at pressures up to 15.5 GPa with a membrane-driven diamond anvil cell. At ambient conditions, diffraction data were consistent with the I4/mcm structure reported previously in the literature for the same composition. Diffraction data collected at high pressures were consistent with tetragonal (or, at least, pseudo-tetragonal) lattice geometry, and no evidence was found for the development of any of the orthorhombic structures identified in other studies of (Ca, Sr)TiO{sub 3} perovskites.more » Additional weak reflections, which could not be accounted for by the normal I4/mcm perovskite structure, were detected in diffraction patterns collected at pressures of 0.9-2.5 GPa, and above {approx}13.5 GPa, however. Small anomalies in the evolution of unit cell volume and tetragonal strain were observed near 3 GPa, coinciding approximately with breaks in slope with increasing pressure of bulk and shear moduli for a sample with the same composition which had previously been reported. The anomalies could be due either to new tetragonal{r_reversible}tetragonal/pseudo-tetragonal phase transitions or to subtle changes in compression mechanism of the tetragonal perovskite structure. - Graphical abstract: Variation of the tetragonal strain, e {sub t} {sub z} , as a function of pressure for Ca{sub 0.35}Sr{sub 0.65}TiO{sub 3}, showing a break in slope in the vicinity of 3-4 GPa.« less
  • To elucidate characteristic oxygen vacancy formation in layered perovskite (Sr, La){sub n+1}Fe{sub n}O{sub 3n+1} with the perovskite layer number: n=3, oxygen vacancy content δ of the (Sr{sub 0.775}La{sub 0.225}){sub 4}Fe{sub 3}O{sub 10−δ} (SLF4310) was investigated using a titration technique and a thermogravimetric analysis. The equilibrium constant K for the reduction reaction: Oo{sup ×}+2Fe{sub Fe}{sup ∙} (Fe{sup 4+})=1/2O{sub 2}+Vo{sup ∙∙}+2Fe{sub Fe}{sup ×}(Fe{sup 3+}) was estimated using the vacancy content δ. The Arrhenius plot of the K reveals slope change at approximately 775 °C. From the Rietveld analysis, the oxygen vacancies are the most remarkable at the O2 (O4) sites at lowermore » (higher) temperatures than about 800 °C, which temperature is approximately comparable with that of slope change in the K. These facts mean that distribution of vacancy sites in the SLF4310 changes at approximately 775 °C, accompanying no structural phase transition. The vacancy distribution change affects to the ion conductivity of the SLF4310. - Graphical abstract: Crystal structure of (Sr{sub 0.775}La{sub 0.225}){sub 4}Fe{sub 3}O{sub 10−δ} (SLF4310) at 1000 °C. Display Omitted - Highlights: • Distribution change of oxygen vacancies is appeared at approximately 775 °C. • The distribution change with no structure phase transition is the first observation. • The vacancy distribution change affects the ion conductivity of the SLF4310.« less
  • The layered perovskite structures of NaYTiO{sub 4} and homologous acid exchange form were investigated via powder X-ray diffraction and high resolution transmission electron microscopy. The NaYTiO{sub 4} layered structure differs from the previous investigation of Blasse et al., by the incorporation of perovskite-like 2 octahedra thick lamellae instead of 1 octahedron thick lamellae and by a stacking of slabs which is primitive instead of I-centered with an (a + b)/2 gliding. The exchange of Na{sup +} cations was performed in an acid medium. This experiments suggests that half of the Y{sup 3+} ions occupy the perovskite like cavities whereas themore » Na{sup +} cations are localized in the interlayer space. Consequently, this structure is probably closer to TlBa{sub 2}CaCu{sub 2}O{sub 7} family compounds than to A{sub n+1}B{sub n}O{sub 3n+1} Ruddlesden-Popper type structure with n = 1.« less