Search

国防科工局核能开发科研项目（cosSYST等热工水力计算分析软件的自主化研发与示范应用）资助

Herein, the effects of different Sr content doping on the crystal structure and electronic structure of La1−xSrxFeO3−δ (LSFO‐x, x = 0, 0.2, 0.5, 0.8, 1.0) are studied by X‐ray diffraction (XRD) and Mössbauer spectroscopy. It is shown in the XRD results that the structure of LSFO‐x changes from orthorhombic (Pnma [#62]) to cubic (Pm‐3m (#221)) to tetragonal (I4/mmm (#139)) with increasing strontium doping. It is shown in Mössbauer spectrum analysis that with the gradual increase of Sr doping, iron ions finally change from +3 oxidation state to +4 oxidation state after passing through an intermediate oxidation state of +3.5. The Fe3.5+ state can result from rapid electron exchange (Fe3+ + Fe4+ ⇋ Fe4+ + Fe3+) between iron ions of different oxidation states within the crystal structure; the study provides some reference for future research to study the effect of iron‐oxidation state on the specific activity of strontium‐doped LaFeO3. [ABSTRACT FROM AUTHOR]

This work has focused on the cluster state of B‐site ions in the rare‐earth perovskite REFepCr1−pO3, and GdFe0.5Cr0.5O3 is taken for instance. This analysis indicates a paramagnetic behavior of the system, which originates from the paramagnetic contribution of the Gd3+. An internal‐field model is used to simplify the superexchange interaction between the A/B‐sites. Furthermore, the cluster state of B‐site ions is computed using the average number of nearest‐neighborhoods. Using Marine Predator Algorithm to fit the experiment data, it is found that Fe–Cr interaction does not conform to the case of ferromagnetic superexchange; therefore, there is no spin glass behavior in this system. Via fitting the Mossbauer spectrum at low temperatures (120 and 12 K), the calculations described above are verified. The calculation gives the hyperfine‐field intervals ΔH of 2.47 and 0.92 T at 120 and 12 K. It is found that B‐site ions tend to form clusters. The arrangement of the ions is random and without the tendency of orderly interval occupation of ions (like double perovskite). The study sheds light on the mechanism of single‐ion clustering and introduces new methods for calculating single‐ion clustering states. It can also be applied to the case of other A‐site ions in perovskite system and is not just limited to p = 0.5 in REBpB'1−pO3. [ABSTRACT FROM AUTHOR]

The effects of pressure on the microstructure and magnetic properties of Co-Fe bistable Prussian blue analogues (PBA) were investigated by Mössbauer spectroscopy and magnetic measurements. Na0.54Co1.23[Fe(CN)6]·7.6H2O was prepared by the co-precipitation method and pressurized at 1–40 MPa using a supercritical CO2 extraction unit. All materials are face-centered cubic with a Néel temperature of about 14 K. The results showed that two electronic configurations existed in the NaCoFe-PBA system at room temperature: FeIIILS-CN-CoIIHS and FeIILS-CN-CoIIILS. The pressure induced the enhancement of antiferromagnetic coupling between Co-Fe ions and controlled the interconversion of the two structures through charge transfer mediated by cyanide bridges. We found that the directions of redox reactions occurring at 0–20 MPa and 20–40 MPa did not coincide, suggesting that there may be more complex interactions between structural and electronic events. [ABSTRACT FROM AUTHOR]

In this paper, LaFe0.75Cr0.25O3 was synthesized by a citric acid combusting sol–gel method. The basic structural information is reflected by XRD. According to Mössbauer spectroscopy, the inhomogeneous distribution of Cr contributes to magnetic dilution, thus appearing the coexistence of singlet and sextet. Simultaneously, the rare superparamagnetic relaxation appears due to "critical superparamagnetism" caused by small magnetic clusters with intervening sizes. Oxygen vacancies of synthesized sample are also found. The DC magnetization curve reveals the magnetization reversal phenomenon, which is related to the competition between the Dzyaloshinsky–Moriya interaction (DMI) and the magnetic anisotropy belonging to single ions. At 300 K, LCFO reveals weak magnetism. No magnetic transition is observed below 400 K. [ABSTRACT FROM AUTHOR]

In this paper, the Prussian blue analogues K0.4Co1.3[Fe(CN)6]•nH2O ([KCoFe]) were synthesized using the coprecipitation method at room temperature, 40, 60, 80 and 100 °C. XRD shows that as the preparation temperature increases, [KCoFe] undergoes structural distortion. The room temperature phase and the high temperature phase are both face-centered cubic (Fm-3 m) structures with lattice constants of 10.230 Å and 9.980 Å, respectively. Mössbauer spectrum analysis showed that due to the increase of synthesis temperature, [KCoFe] has undergone charge transfer induced spin transition. Part of paramagnetic structure: FeІІІ ( t 2 g 5 , S = 1/2)–CN–CoІІ ( t 2 g 5 e g 2 , S = 3/2) was transformed into diamagnetic structure: FeІІ ( t 2 g 6 , S = 0)–CN–CoІІІ ( t 2 g 6 , S = 0). This work provides new ideas for designing new Prussian blue analogues magnetic materials. Keyword: Thermal-induced, Prussian blue analogues, Structural distortion, Charge transfer. [ABSTRACT FROM AUTHOR]

Laminectomy and facetectomy are surgical techniques used for decompression of the cervical spinal stenosis. Recent in vitro and finite element studies have shown significant cervical spinal instability after performing these surgical techniques. However, the influence of degenerated cervical disk on the biomechanical responses of the cervical spine after these surgical techniques remains unknown. Therefore, a three-dimensional nonlinear finite element model of the human cervical spine (C2-C7) was created. Two types of disk degeneration grades were simulated. For each grade of disk degeneration, the intact as well as the two surgically altered models simulating C5 laminectomy with or without C5-C6 total facetectomies were exercised under flexion and extension. Intersegmental rotational motions, internal disk annulus, cancellous and cortical bone stresses were obtained and compared to the normal intact model. Results showed that the cervical rotational motion decreases with progressive disk degeneration. Decreases in the rotational motion due to disk degeneration were accompanied by higher cancellous and cortical bone stress. The surgically altered model showed significant increases in the rotational motions after laminectomies and facetectomies when compared to the intact model. However, the percentage increases in the rotational motions after various surgical techniques were reduced with progressive disk degeneration. [DOI: 10.1115/1.1835364] Keywords: Stress Analysis, Biomechanics, Finite Element, Laminectomy, Facetectomy, Surgery, Spondylosis