ترغب بنشر مسار تعليمي؟ اضغط هنا

Structural properties of Pb3Mn7O15 determined from high-resolution synchrotron powder diffraction

188   0   0.0 ( 0 )
 نشر من قبل Julia Rasch
 تاريخ النشر 2008
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We report on the crystallographic structure of the layered compound Pb3Mn7O15. Previous analysis based on laboratory X-ray data at room temperature gave contradictory results in terms of the description of the unit cell. Motivated by recent magnetic bulk measurements of this system, we re-investigated the chemical structure with high-resolution synchrotron powder diffraction at temperatures between 15 K and 295 K. Our results show that the crystal structure of stoichiometric Pb3Mn7O15 has a pronounced 2-dimensional character and can be described in the orthorhombic space group Pnma.



قيم البحث

اقرأ أيضاً

We present a structural analysis of the multi-layer graphene-4HSiC(000-1}) system using Surface X-Ray Reflectivity. We show for the first time that graphene films grown on the C-terminated (000-1}) surface have a graphene-substrate bond length that i s very short (0.162nm). The measured distance rules out a weak Van der Waals interaction to the substrate and instead indicates a strong bond between the first graphene layer and the bulk as predicted by ab-initio calculations. The measurements also indicate that multi-layer graphene grows in a near turbostratic mode on this surface. This result may explain the lack of a broken graphene symmetry inferred from conduction measurements on this system [C. Berger et al., Science 312, 1191 (2006)].
We performed neutron powder diffraction measurements on (Bi$_{0.5}$Na$_{0.5+x}$)TiO$_3$ and (Bi$_{0.5+y}$Na$_{0.5}$)TiO$_3$ to study structural evolution induced by the non-stoichiometry. Despite the non-stoichiometry, the local structure ($r$$leq$ 3 .5 {AA}) from the pair distribution function analysis is barely affected by the sodium deficit of up to -5 mol%. With increasing pair distance, however, the atomic pair correlations weaken due to the disorder caused by the sodium deficiency. Although the sodium and the bismuth share the same crystallographic site, their non-stoichiometry have rather opposite effects as revealed from a distinctive distortion of the Bragg peaks. In addition, Rietveld refinement demonstrates that the octahedral tilting is continually suppressed by the sodium deficit of up to -5 mol%. This is contrary to the effect of the bismuth deficiency, which enhances the octahedral tilting.
The controversies about the structure of the true ground state of pseudorhombohedral compositions of Pb(ZrxTi1-x)O3 (PZT) are addressed using a 6% Sr2+ substituted sample with x=0.550. Sound velocity measurements reveal a phase transition at Tc~279K. The temperature dependence of FWHM of (h00)pc peaks and the unit cell volume also show anomalies around 279K even though there is no indication of any change of space group in the synchrotron X-ray powder diffraction (SXRD) patterns. The neutron powder diffraction patterns reveal appearance of superlattice peaks below Tc~279K confirming the existence of an antiferrodistortive phase transition. The Rietveld analysis of the room temperature and low temperature SXRD data below Tc shows that the structure corresponds to single monoclinic phase in the Cm space group while the analysis of neutron powder diffraction data reveals that the structure of the ground state phase below Tc corresponds to the Cc space group. Our analysis shows that the structural models for the ground state phase based on R3c space group with or without the coexistence of the room temperature monoclinic phase in the Cm space group can be rejected.
The epitaxial growth of complex oxide thin films provide three avenues to generate unique properties: the ability to influence the 3-dimensional structure of the film, the presence of a surface, and the generation of an interface. In all three cases, a clear understanding of the resulting atomic structure is desirable. However, determining the full structure of an epitaxial thin film (lattice parameters, space group, atomic positions, surface reconstructions) on a routine basis is a serious challenge. In this paper we highlight the remarkable information that can be extracted from both the Bragg scattering and inelastic multiple scattering events that occur during Reflection High Energy Electron Diffraction. We review some methods to extract structural information and show how mature techniques used in other fields can be directly applied to the {em in-situ} and real-time diffraction images of a growing film. These collection of techniques give access to both the epitaxially influenced 3 dimensional bulk structure of the film, and any reconstructions that may happen at the surface.
Perovskite photovoltaic ABX$_3$ systems are being studied due to their high energy-conversion efficiencies with current emphasis placed on pure inorganic systems. In this work, synchrotron single-crystal diffraction measurements combined with second harmonic generation measurements reveal the absence of inversion symmetry below room temperature in CsPbBr$_3$. Local structural analysis by pair distribution function and X-ray absorption fine structure methods are performed to ascertain the local ordering, atomic pair correlations, and phase evolution in a broad range of temperatures. The currently accepted space group assignments for CsPbBr$_3$ are found to be incorrect in a manner that profoundly impacts physical properties. New assignments are obtained for the bulk structure: $Im$$bar{3}$ (above $sim$ 410 K), $P$2$_1$/$m$ (between $sim$ 300 K and $sim$ 410 K), and the polar group $Pm$ (below $sim$ 300 K), respectively. The newly observed structural distortions exist in the bulk structure consistent with the expectation of previous photoluminescence and Raman measurements. High-pressure measurements reveal multiple low-pressure phases, one of which exists as a metastable phase at ambient pressure. This work should help guide research in the perovskite photovoltaic community to better control the structure under operational conditions and further improve transport and optical properties.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا