We report on an elastic neutron scattering study of the charge correlations in La2–xSrx CoO4 with x = 1/3, 0.4 and 0.5. We found that the checkerboard charge ordering correlations present in the x = 0.5 sample persist in the x = 0.4 and 1/3 materials. These checkerboard charge ordering correlations are robust and explain the occurrence of nano‐phase separation in layered cobaltates for Sr‐concentrations away from half‐doping. The half‐integer reflections then arise from the nanometer‐sized hole‐rich regions (blue areas in title figure) instead of the undoped ones (red areas in title figure). The appearance of nano‐phase separation is an important ingredient for understanding the formation of hour‐glass shaped magnetic excitation spectra in La2–xSrx CoO4.
Nano‐phase separation in La2–xSrx CoO4 (schematically). Red areas: undoped La2CoO4 islands, blue areas: checkerboard charge ordered regions; black, green and blue balls represent nonmagnetic Co3+ ions, magnetic Co2+ ions and oxygen ions, respectively; green arrows indicate Co2+ spins [1, 2]. 相似文献
利用蒙特卡罗程序FLUKA模拟计算了聚乙烯慢化球和辅助材料慢化球对低能中子到高能中子的响应函数曲线。结果表明,对纯聚乙烯球来说,随着聚乙烯层厚度的增加,响应曲线峰逐步右移,峰值在高能区有所下降,对20 Me V以上的中子,无论纯聚乙烯球的尺寸有多大,其响应均下降到很低的程度;对辅助材料慢化球来说,中子能量小于1 Me V时,辅助材料慢化球与聚乙烯慢化球的响应曲线相似,但当中子能量大于20 Me V时,中子与辅助材料层发生(n,xn)反应,慢化球的响应呈显著上升趋势。分析计算结果,最终能够确定宽能谱多球中子谱仪的尺寸组合。 相似文献
Complementary structural and vibrational spectroscopy study of bromanilic acid:2,3,5,6-tetramethylpyrazine (BrA:TMP) 1:1 cocrystal is reported. The crystallographic structure was determined by means of single-crystal X-ray diffraction and can be described as a stacked net of hydrogen-bonded TMPH+⋯BrA−⋯BrA−⋯TMPH+ moieties. The structural analysis was supported by 13CP/MAS NMR study. The complementary vibrational analysis was performed by combining optical (infrared, Raman, terahertz) and inelastic neutron scattering spectroscopy with the state-of-the-art solid–state density functional theory (DFT) computations, which have proven to be superior to the hybrid cluster modeling approach. An excellent agreement between theoretical and experimental data was observed over the entire spectral range, allowing for deep understanding of the vibrational properties. While the primary hydrogen-bonding interactions are limited to the above quoted structural units, the system revealed very little dispersion of the phonon branches, manifested mainly in the intermolecular vibrations range. Moreover, the studied phase does not exhibit any mechanical instability, which could suggest a displacive structural transformation tendency. 相似文献
The design and synthesis of organic materials with a narrow emission band in the longer wavelength region beyond 510 nm remain a great challenge. For constructing narrowband green emitters, we propose a unique molecular design strategy based on frontier molecular orbital engineering (FMOE), which can integrate the advantages of a twisted donor–acceptor (D-A) structure and a multiple resonance (MR) delayed fluorescence skeleton. Attaching an auxiliary donor to a MR skeleton leads to a novel molecule with twisted D-A and MR structure characteristics. Importantly, a remarkable red-shift of the emission maximum and a narrowband spectrum are achieved simultaneously. The target molecule has been employed as an emitter to fabricate green organic light-emitting diodes (OLEDs) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.69) and a maximum external quantum efficiency (EQE) of 27.0 %. 相似文献