Abstract
An effort to synthesize the Cu(I) variant of a lead-free double perovskite isostructural with Cs2AgInCl6 resulted in the formation of Cs3Cu4In2Cl13 nanocrystals with an unusual structure, as revealed by single-nanocrystal three-dimensional electron diffraction. These nanocrystals adopt a A2BX6 structure (K2PtCl6 type, termed vacancy ordered perovskite) with tetrahedrally coordinated Cu(I) ions. In the structure, 25% of the A sites are occupied by [Cu4Cl]3+ clusters (75% by Cs+), and the B sites are occupied by In3+. Such a Cs3Cu4In2Cl13 compound prepared at the nanoscale is not known in the bulk and is an example of a multinary metal halide with inorganic cluster cations residing in A sites. The stability of the compound was supported by density functional theory calculations that also revealed that its bandgap is direct but parity forbidden. The existence of the Cs3Cu4In2Cl13 structure demonstrates that small inorganic cluster cations can occupy A sites in multinary metal halides.
Highlights
Perovskites (ABX3) and perovskite-related compounds are some of the most chemically diverse crystal structures with many possible substitutions at A and/or B sites, as demonstrated in oxide systems.[1−3] multinary metal halides are very versatile: many types of substitutions are known to be possible at the B sites[4−6] and A sites [can be filled with both atomic and molecular organic cations].7−9 substitutions at the A site in multinary metal halides are mostly limited to monovalent cations,[10] with rare examples of divalent organic cations, such as piperazine-1,4-diium (C4H12N42+) and a few others.[11−14]
One way to describe Cs3Cu4In2Cl13 is to relate it to a vacancy (□) ordered perovskite [A2BX6 type, (Cs3,Cu4Cl)(In2,□2)Cl12] in which 25% of the A sites are occupied by [Cu4Cl]3+ clusters and the remaining 75% by Cs+, while the B sites are occupied by In3+ ions
The atmosphere was switched to nitrogen, and the temperature was increased to 145 °C
Summary
Perovskites (ABX3) and perovskite-related compounds are some of the most chemically diverse crystal structures with many possible substitutions at A and/or B sites, as demonstrated in oxide systems.[1−3] multinary metal halides are very versatile: many types of substitutions are known to be possible at the B sites (e.g., double and vacancy ordered perovskites)[4−6] and A sites [can be filled with both atomic (inorganic) and molecular organic cations].7−9 substitutions at the A site in multinary metal halides are mostly limited to monovalent cations (cesium, methylammonium, formamidinium, etc.),[10] with rare examples of divalent organic cations, such as piperazine-1,4-diium (C4H12N42+) and a few others.[11−14]. A good Rietveld refinement could be achieved only by considering a completely disordered model in space group Fm3̅m, where each of the eight Cs sites in the unit cell was partially occupied by a (Cu4Cl)3+ cluster with a probability of 0.25 (Figure 3a) (see Table S5 for further details). The structural solution retains the trace of disorder through a higher potential peak of the Cl atom substituting Cs. For a comparison, Figure S4 groups together the following XRD patterns: (a) the experimental pattern of the NCs synthesized at 145 °C, (b) the computed band structure on the experimental primitive cubic unit cell with space group Pn3̅m and Cs3Cu4In2Cl13 stoichiometry.
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