Ag-Mg antisite defect induced high thermoelectric performance of α-MgAgSb

Engineering atomic-scale native point defects has become an attractive strategy to improve the performance of thermoelectric materials. Here, we theoretically predict that Ag-Mg antisite defects as shallow acceptors can be more stable than other intrinsic defects under Mg-poor-Ag/Sb-rich conditions. Under more Mg-rich conditions, Ag vacancy dominates the intrinsic defects. The p-type conduction behavior of experimentally synthesized ¿-MgAgSb mainly comes from Ag vacancies and Ag antisites (Ag on Mg sites), which act as shallow acceptors. Ag-Mg antisite defects significantly increase the thermoelectric performance of ¿-MgAgSb by increasing the number of band valleys near the Fermi level. For Li-doped ¿-MgAgSb, under more Mg-rich conditions, Li will substitute on Ag sites rather than on Mg sites and may achieve high thermoelectric performance. A secondary valence band is revealed in ¿-MgAgSb with 14 conducting carrier pockets

Applications of Nanomaterials in Electrogenerated Chemiluminescence Biosensors

Electrogenerated chemiluminescence (also called electrochemiluminescence and abbreviated ECL) involves the generation of species at electrode surfaces that then undergo electron-transfer reactions to form excited states that emit light. ECL biosensor, combining advantages offered by the selectivity of the biological recognition elements and the sensitivity of ECL technique, is a powerful device for ultrasensitive biomolecule detection and quantification. Nanomaterials are of considerable interest in the biosensor field owing to their unique physical and chemical properties, which have led to novel biosensors that have exhibited high sensitivity and stability. Nanomaterials including nanoparticles and nanotubes, prepared from metals, semiconductor, carbon or polymeric species, have been widely investigated for their ability to enhance the efficiencies of ECL biosensors, such as taking as modification electrode materials, or as carrier of ECL labels and ECL-emitting species. Particularly useful application of nanomaterials in ECL biosensors with emphasis on the years 2004-2008 is reviewed. Remarks on application of nanomaterials in ECL biosensors are also surveyed

Study on Crack Propagation of the Tunnel Model under Dynamic Loading

Crack defects make it difficult to predict the dynamic fracture of tunnel specimens under an impact load. To study the impact of the velocity and crack location on a roadway under dynamic load, specimens with tunnel-type voids were made using polymethyl methacrylate. The split-Hopkinson bar was used as the loading method, and a digital laser dynamic caustics system was used to observe the fracture process of the specimens. The dynamic fracture process was evaluated by the crack propagation velocity, displacement, and dynamic stress intensity factor. To predict and verify the test results, ABAQUS was used to simulate the test process. It was found that the results of the simulated combinations of the crack propagation path and initial fracture toughness change law are consistent with the test results. The initial fracture toughness and the peak value of the crack propagation velocity increased with the increase of the impact velocity. The crack propagation law and trajectory were affected by the location of the prefabricated cracks

A class of rare antiferromagnetic metallic oxides: double perovskite AMn(3)V(4)O(12) (A = Na+, Ca2+, and La3+) and the site-selective doping effect

We have investigated the structural, electronic, and magnetic properties of A-site-ordered double-perovskitestructured oxides, AA\u273B4O12 (A = Na, Ca, and La) with Mn and V at A\u27 and B sites, respectively, using firstprinciple calculations based on the density functional theory. Our calculation results show that the antiferromagnetic phase is the ground state for all the compounds. By changing the A-site ions from Na+ to Ca2+ and then to La3+, the transfer of charge between Mn and O ions was changed from 1.56 to 1.55 and then to 1.50, and that between the V and O ions changed from 2.01 to 1.95 and then to 1.93, revealing the cause for the unusual site-selective doping effect. Mn 3d electrons dominate the magnetic moment and are localized, with an intense hybridization with O 2p orbitals, which indicates that the magnetic exchange interaction between Mn ions is mediated through O and that the super exchange mechanism will take effect. These materials have a large one-electron bandwidth W, and the ratio of the on-site Coulomb repulsion U to W is less than the critical value (U/W)c, which leads to metallic behavior of AMn3V4O12. This is further evidenced by the large number of free electrons contributed by V at the Fermi surface. These calculations, in combination with the reported experimental data, prove that these double perovskites belong to the rare antiferromagnetic metallic oxides

Machine Learning Accelerated Discovery of Promising Thermal Energy Storage Materials with High Heat Capacity

Thermal energy storage offers numerous benefits by reducing energy consumption and promoting the use of renewable energy sources. Thermal energy storage materials have been investigated for many decades with the aim of improving the overall efficiency of energy systems. However, finding solid materials that meet the requirement of high heat capacity has been a grand challenge for material scientists. Herewith, by training various machine learning models on 3377 high-quality data from full density functional theory (DFT) calculations, we efficiently search for potential materials with high heat capacity. We build four traditional machine learning models and two graph neural network models. Cross-comparison of the prediction performance and model accuracy was conducted among different models. The deeperGATGNN model exhibits high prediction accuracy and is used for predicting the heat capacity of 32,026 structures screened from the open quantum material database. We gain deep insight into the correlation between heat capacity and structure descriptors such as space group, prototype, lattice volume, atomic weight, etc. Twenty-two structures were predicted to possess high heat capacity, and the results were further validated with DFT calculations. We also identified one special structure, namely, MnIn2Se4, with space group no. 227 (Fd3̅m), that exhibits extremely high heat capacity, even higher than that of the Dulong–Petit limit at room temperature. This study paves the way for accelerating the discovery of novel thermal energy storage materials by combining machine learning with minimal DFT inquiry

Tuning magnetism by biaxial strain in native ZnO

Magnetic ZnO, one of the most important diluted magnetic semiconductors (DMS), has attracted great scientific interest because of its possible technological applications in optomagnetic devices. Magnetism in this material is usually delicately tuned by the doping level, dislocations, and local structures. The rational control of magnetism in ZnO is a highly attractive approach for practical applications. Here, the tuning effect of biaxial strain on the d0 magnetism of native imperfect ZnO is demonstrated through first-principles calculations. Our calculation results show that strain conditions have little effect on the defect formation energy of Zn and O vacancies in ZnO, but they do affect the magnetism significantly. For a cation vacancy, increasing the compressive strain will obviously decrease its magnetic moment, while tensile strain cannot change the moment, which remains constant at 2 µB. For a singly charged anion vacancy, however, the dependence of the magnetic moment on strain is opposite to that of the Zn vacancy. Furthermore, the ferromagnetic state is always present, irrespective of the strain type, for ZnO with two zinc vacancies, 2VZns. A large tensile strain is favorable for improving the Curie temperature and realizing room temperature ferromagnetism for ZnO-based native semiconductors. For ZnO with two singly charged oxygen vacancies, 2VO+s, no ferromagnetic ordering can be observed. Our work points the way to the rational design of materials beyond ZnO with novel non-intrinsic functionality by simply tuning the strain in a thin film form