Review of Spin–Orbit Coupled Semimetal SrIrO3 in Thin Film Form

Spin–orbit coupling, locking the momentum of an electron to its spin, has been shown essential for giving rise to many novel physical behaviors. SrIrO₃ is a typical metallic member of the strong spin–orbit coupling iridate family. Its orthorhombic phase has been confirmed as a paramagnetic semimetal resulted from the interplay among spin–orbit coupling, electron correlation, and crystal field, and was theoretically predicted to host versatile topological phases. This article reviews the current knowledge on the preparation and the tunable properties of orthorhombic SrIrO₃ films. Experiments have demonstrated that orthorhombic SrIrO₃ can be successfully synthesized as films under substrate lattice constraint without high pressure, and the films frequently display metal-insulator transition due to disorder and weak-antilocalization owing to spin-orbit coupling. The properties of orthorhombic SrIrO₃ film are sensitive to the rotation and tilting of the IrO₆ octahedral, and consequently can be significantly tuned through strain engineering. Simultaneously, thickness-dependent size effect is also remarkable in SrIrO₃ films. The accumulated research on SrIrO₃ films suggests an urgent demand for research on superlattices constructed with orthorhombic SrIrO₃, to better understand the mechanism of the electron structure evolution, and thus the relevant magnetic states and topological phases in orthorhombic SrIrO₃ and its family.     

稀土金属Ce3+掺杂ZnO材料的光催化机理

通过溶胶凝胶法制备了光催化活性更高的Ce∶ZnO复合粉体光催化材料,并采用X射线衍射(XRD)、电子顺磁共振(EPR)、紫外可见光谱(UV-Vis)技术对所制备的粉体样品的晶体种类及结构、自由基种类及含量、光催化效率进行表征分析。复合样品的X射线衍射测试结果显示,随着掺杂浓度的增加,先后检测到CeO₂的(111)和(200)晶面特征峰,且衍射峰强度逐渐增强。此外,适量的掺杂(c(Ce³⁺)=2%)可减小ZnO晶体的晶粒尺寸。电子顺磁共振测试结果显示,Ce∶ZnO复合光催化材料中存在三类自由基,分别是Zn-H络合物、正一价氧空位、CeO₂表面吸附的超氧根离子。紫外可见光谱测试表明,适量的掺杂可有效提高ZnO催化剂的光催化活性,综合分析显示,ZnO光催化活性提高的主要原因是Ce³⁺的掺入使得材料中电子数量增多,进而提高了活性自由基·O^-₂的数量。本文通过EPR技术和XRD衍射技术,成功表征了Ce³⁺掺杂对ZnO材料中自由基种类合成的影响过程,并结合UV-Vis技术,对Ce∶ZnO复合材料光催化降解甲基橙的过程中的电子转移过程作出了合理的解释。     

Cover Feature: How Different are the Diamagnetic and Paramagnetic Contributions to Off-Nucleus Shielding in Aromatic and Antiaromatic Rings? (ChemPhysChem 9/2023)

The spatial variations in the diamagnetic and paramagnetic contributions to the off-nucleus isotropic shielding, , and to the zz component of the off-nucleus shielding tensor, , around benzene (C₆H₆) and cyclobutadiene (C₄H₄) are investigated using complete-active-space self-consistent field wavefunctions. Despite the substantial differences between and around the aromatic C₆H₆ and the antiaromatic C₄H₄, the diamagnetic and paramagnetic contributions to these quantities, and , and and , are found to behave similarly in the two molecules, shielding and deshielding, respectively, each ring and its surroundings. The different signs of the most popular aromaticity criterion, the nucleus-independent chemical shift (NICS), in C₆H₆ and C₄H₄ are shown to follow from a change in the balance between the respective diamagnetic and paramagnetic contributions. Thus, the different NICS values for antiaromatic and antiaromatic molecules cannot be attributed to differences in the ease of access to excited states only; differences in the electron density, which determines the overall bonding picture, also play an important role.     

Studies on the EPR parameters and local angular distortion for the tetragonal Cu2+ center in CaWO4 crystal

The electron paramagnetic resonance (EPR) parameters—g factors g_i (i = || and ⊥) and hyperfine structure constants A_i (M) and A_i(N), with M and N belonging to isotopes ⁶³Cu²⁺ and ⁶⁵Cu²⁺—and local structure of Cu²⁺ ion occupying W⁶⁺ site in CaWO₄ crystal are theoretically studied based on the perturbation formulas of these parameters for a 3d⁹ ion under tetragonally elongated tetrahedra. In these formulas, the ligand orbital (LO) and spin–orbit coupling (SOC) contributions are included due to the shorter impurity-ligand distance R (≈1.83 Å) and hence the strong covalency of the studied [CuO₄]⁶⁻ cluster, and the related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way; meanwhile, the required crystal field (CF) parameters for the tetragonally distorted tetrahedron (TDT) are estimated from the superposition model and the local structure of the impurity Cu²⁺ center. According to the calculation, the bond angle θ between the four equivalent Cu²⁺-O²⁻ bonds and the C₄ axis in the CaWO₄:Cu²⁺ is found to be about 2.1° smaller than that (θ₀ ≈ 54.74°) for an ideal tetrahedron due to the Jahn–Teller (JT) effect and the size mismatch. The fitted results agree well with the observed values, and the validity of the present assignment for the local structure of the Cu²⁺ center is also discussed.     

Titanium dioxide nanoparticles heavily doped with niobium: A light-induced electron paramagnetic resonance study

Light-induced electron paramagnetic resonance (EPR) spectra of titanium dioxide nanoparticles heavily doped with niobium(v) are studied. At low temperatures, the EPR signal caused by interband illumination is associated with paramagnetic Ti³⁺ sites in anatase, which, as the temperature rises above 210 K, are discharged to the non-paramagnetic Ti⁴⁺ state due to the escape of trapped photoelectrons and their recombination with holes. The temperature dependence of the integral EPR signal has a non-Curie character, especially in the temperature range where the discharge of Ti³⁺ centers is already significant.     

Molecular structure,spectroscopic, electronic and physicochemical properties of 7,8-dihydroxyflavone hydrate compound using first theory principle

The present investigation involves the structure-based drug design and the functional evaluation of flavone based compound that can be utilized for breast cancer therapy, and it provides a way to create platforms for chemotherapy of breast cancer treatments. The 7,8-dihydroxyflavone hydrate (7DHFH) molecule was structurally characterized by spectroscopic techniques such as FT-IR/Raman, and EPR spectral analysis, which were compared with the DFT methods using Gaussian09 software packages. The complete assignments of the fundamental vibrational modes were obtained using potential energy distribution.The DFT results show a good agreement with the all experimental results. A DFT study on frontier molecular orbital analysis is used to calculate the HOMO- LUMO energies and charge transfer or conjugative interaction taking place within the molecular system and also other molecular parameters, viz. chemical hardness, softness, ionization potential, electron affinity, electrophilicity index, and electronegativity. Furthermore, the drug likeness properties were also calculated, thus allowing us to identify the present compound as a potential anticancer agent. Molecular docking results revealed the bioactive candidate displayed the best free-energy score towards the target proteins through forming strong hydrogen bonds with the amino acid residues. Finally, the cytotoxic activity of the 7DHFH confirms the anticancer activity against human breast cancer cell lines by MTT assays.