Unravelling the atomic-level chemical structure, slow phase conversion or degradation pathways and rapid halogen hopping of cesium tin(ii) halide perovskites using solid-state 119Sn and 133Cs NMR spectroscopy.
Predictions of high thermoelectric performance in RECuZnP2 were verified by elastic, electrical, and thermal measurements. Low thermal conductivities result from strong anharmonicity, with electron transport limited by polar optical phonons.
With
their exceptional optoelectronic features, metal halide perovskites
(MHPs) are pushing the next wave of energy-related materials research.
Heretofore, most solid-state nuclear magnetic resonance (NMR) investigations
have focused on readily accessible nuclei. In contrast, the halogen
environments have been avoided due to their challenging quadrupolar
nature. Here, we report a rapid 35/37Cl NMR strategy for
MHPs, halide double perovskites (HDPs), and perovskite-inspired (PI)
materials embracing ultra-wideline acquisition approaches at moderate
and ultrahigh magnetic fields. The observed quadrupolar NMR parameters
(C
Q and η), supported by GIPAW–DFT
computations, provide an analytical fingerprint revealing distinct
features for chemically unique Cl environments sensitive to ion mixing,
dimensionality, cell volume, and Cl coordinating polyhedra. Moreover,
we report resolution between two nearly identical and two distinct
Cl environments of 3D and 2D Cs-based lead halide perovskites, respectively.
These results reveal a strategy for a routine and robust spectroscopic
approach to analyze local Cl chemical environments in metal halide
perovskites that can be extended broadly to other halogen-containing
semiconductors.
Mixed
Sn–Pb halide perovskites are more stable at ambient
conditions and can be tuned to give narrower band gaps than the all-Pb-containing
counterparts (APbX3) used as photovoltaic materials. In
the series CsSn
x
Pb1–x
Br3, the crystal structure evolves from
orthorhombic (space group Pnma for x = 0–0.8) to cubic (space group Pm
m for x = 1), and the band gap decreases for Sn-richer compositions.
It
previously was unclear how the physical properties are related to
structural changes entailed by the Sn–Pb mixing because the
short- versus long-range arrangements have not been well characterized.
Solid-state NMR spectroscopy of several NMR-active nuclei (119Sn, 133Cs, and 207Pb) supports the occurrence
of complete disorder, with PbBr6 and SnBr6 octahedra
distributed in random arrangements throughout the entire structure
with no evidence for phase segregation. Compounds prepared by solvent-assisted
vs solvent-free routes are compared and show differences in their
degree of crystallinity and optical absorption properties.
Bivalent cations (M = Ni 2+ , Co 2+ , Mg 2+ ) with different doping contents (x = 0.1, 0.2, 0.3, 0.4, 0.5) were incorporated for vanadium in the Na 3+x V 2−x M x (PO 4 ) 3 (NVP), yielding enhanced rate performance and capacity retention. Successful doping of these cations in the NVP structure was confirmed by powder X-ray diffraction (PXRD), vibrational FT-IR spectroscopy, and scanning electron microscopy (SEM) techniques. The improved electrochemical performance of substituted NVP cathode has been correlated to effective Na ion migration, which improved kinetics of charging and discharging properties. Mg 2+ was possible to dope up to x = 0.5 in the NVP structure, which exhibited a superior electrochemical performance compared to that of Ni 2+ -and Co 2+ -doped NVP samples. The Mg 2+ -doped NVP electrode exhibited fast Na ion kinetics with a specific capacity of 70 mAh g −1 at a 20 C rate. The oxidation state of the vanadium in the Mg 2+ -substituted NVP was investigated by using X-ray photoelectron spectroscopy (XPS).
A cyano-tetraethylene glycol functionalized amphiphilic cyclodextrin forms liquid crystalline self-assembly that shows promising ion conductivity (Li+).
Chalcogenides are an important class of materials that exhibit tailorable optoelectronic properties accessible through chemical modification. For example, the minerals kesterite, stannite, and velikite (Cu2MSnS4, where M=Zn, Cd or Hg,...
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