To explore the significance of impurity doping in power conversion efficiency, quaternary gradient CdZnSSe alloy nanocrystals (NCs) and its Mn-doped analogues were synthesized by high-temperature pyrolysis. The undoped and Mn-doped CdZnSSe alloy NCs have been characterized by employing high-resolution TEM, X-ray diffraction, energy-dispersive X-ray spectroscopy, and electron paramagnetic resonance spectroscopy measurements. A low-temperature injection of chalcogens led to a gradient interface in the alloy, comprised of a CdSe/CdS/ZnSe/ZnS nanostructure. Both steady-state and ultrafast time-resolved absorption studies suggested the formation of a charge-transfer (CT) state due to the inner quasi-type II CdSe/CdS part of the gradient CdZnSSe alloy NCs, in which electrons are delocalized throughout the conduction band (CB) of both CdSe and CdS. The CT-state bleach recovery kinetics gave an additional slow electron cooling component (8 ps) in the undoped alloy NCs, which has been assigned to electron equilibration in the delocalized CB before recombination (or trapping). Interestingly, in the presence of dopant Mn, the slow electron cooling component became even more sluggish at 10 ps due to Mn-mediated electron cooling, in which Mn acts as an electron storage center. An unprecedented increase in the photocurrent conversion efficiency (PCE) of approximately 30 % from (3.3±0.11) to (4.29±0.07) % was observed in the Mn-doped gradient alloy compared with the undoped alloy.

To take account of the interface in the nanocrystal (NC) materials, we have synthesized high quantum yield gradient CdZnSSe alloy NC having minimal involvement of interface (G-300) through high temperature (300 °C) pyrolysis and investigated the charge carrier dynamics. The performance was unraveled through femtosecond transient absorption studies. A gradient alloy of CdZnSSe (G-250) at low alloying temperature (250 °C) was also synthesized where several interfaces were present in the form CdSe/CdS/ZnSe/ZnS within the alloy material along with other deep traps as well as surface defects. The successful formulation of minimal involvement of interface in G-300 alloy has been envisaged through its blue-shifted optical absorption spectrum as compared to the G-250 alloy due to interionic diffusion of less reactive Zn and S toward the core of the material at elevated reaction temperatures that widen the band gap. Unlike the G-250 analogue, no charge transfer (CT) state was observed in the G-300 alloy, which also suggests the nonexistence of a CdSe/CdS gradient type structure otherwise present for the G-250 analogue. The slow electron cooling time of 4 ps in the G-250 alloy is found to be absent in the G-300 alloy, which can be attributed to minimal involvement of gradient structure otherwise, where electron–hole decoupling leads to slower electron cooling. It has been observed that although the absorption cross-section of G-300 alloy is lower in the solar spectrum as compared to the G-250 analogue, photocurrent conversion efficiency (PCE) measurements of G-300 show promising 4.5% PCE due to smooth electron transfer to TiO2 through the interface free NCs whereas the G-250 analogue shows only 3.5% PCE. Our investigation suggests that engineering with alloys having less gradient structure and without any boundary restrictions can lead us to new perceptions regarding the design and development of higher efficient quantum dot sensitized solar cell (QDSSC).

R-Nb2O5 has minimal structure changes with cycling and symmetric cycling profiles. With Wadsley–Roth ‘slabs’ and an ‘idealized’ V2O5 structure, metastable R-Nb2O5 bridges understanding of two well-studied families of Li-ion battery electrodes.

The intermetallic 11 Al 4 Fe 1.7 Si phase is of interest for high-temperature structural application due to its combination of low density and high strength. We determine the crystal structure of the 11 phase through a combination of powder neutron diffraction and density functional theory calculations. Using Pawley and Rietveld refinements of the neutron diffraction data provides an initial crystal structure model. Since Al and Si have nearly identical neutron scattering lengths, we use density-functional calculations to determine their preferred site occupations. The 11 phase exhibits a hexagonal crystal structure with space group 6 3 ∕ and lattice parameters of = 7.478 Å and = 7.472 Å. The structure comprises five Wyckoff positions; Al occupies the 6ℎ and 12 sites, Fe the 2 and 6ℎ sites, and Si the 2 sites. We observe site disorder and partial occupancies on all sites with a large fraction of 80% Fe vacancies on the 2 sites, indicating an entropic stabilization of the 11 phase at high temperature.

As batteries are employed in larger numbers and for increasingly diverse applications, there is interest in electrode materials with improved safety, availability, and cost relative to commercial electrodes. Early transition metal oxides are one alternative material family showing promise, especially for high rate applications. However, we do not yet have a strong understanding of the role of composition, structure, and structural evolution with cycling for these materials, which tend to have large unit cells and complex structures.We report here the synthesis, energy storage behavior, and atomic structure evolution during cycling for several metastable niobates featuring crystallographic shear planes. Ex situ and operando X-ray diffraction, along with complementary methods and first principles calculations, allow us to identify atomic structure changes and relate them to cycling performance and properties, especially ionic conductivity. The fundamental understanding established through study of these are related materials can help to establish new fundamental understanding of the atomic structure and chemical motifs that support fast ion transport, thus supporting the selection and design of electrode materials for the quickly-evolving energy landscape.