Jahn−Teller Distortion-Stabilized Halide Double Perovskites with Unusual Rock-Salt-type Ordering of Divalent B-Site Cations

Abstract

Halide double perovskites A 2 B(I)B(III)X 6 , where the monovalent B(I) and trivalent B(III) cations adopt a rock-salt-ordered arrangement primarily due to their large charge difference and ionic radius difference, have attracted substantial interest in the field of optoelectronics. On the other hand, the combinations of two divalent B-site cations usually result in AB(II)′ 0.5 B(II)″ 0.5 X 3 perovskite solid solutions due to the zero charge difference, rather than the rock-salt-ordered A 2 B(II)′B(II)″X 6 double perovskites. In this work, we report the theoretical design and experimental verification of A 2 B(II)′B(II)″X 6 halide double perovskites with unusually rock-salt-ordered divalent B-site cations. Through theoretical calculations, we demonstrate that introducing divalent transition metal cations with partially filled d orbitals into the double perovskite structure can produce significant Jahn−Teller distortions and thus stabilize the rock-salt-ordered double perovskite structure. Among the considered compounds, Cs 2 HgCuCl 6 , Cs 2 HgPdCl 6 , and Cs 2 HgPtCl 6 were predicted to be thermodynamically stable. Experimentally, Cs 2 HgCuCl 6 and Cs 2 HgPdCl 6 were successfully synthesized as representative examples of the A 2 B(II)′B(II)″X 6 halide double perovskites. The synthesized pure-phase Cs 2 HgCuCl 6 exhibits a small bandgap of 1.08 eV that is suitable for visible light absorption. Our work provides an approach for designing novel double perovskites with two kinds of divalent cations, which expands the large family of halide double perovskites for optoelectronic applications.

Molybdenum chloride double perovskites: dimensionality control of optical and magnetic properties

“… 1 In some cases, such as Cs 2 Hg II M II Cl 6 (M II = Cu or Pd), coordination geometry can drive the B-site metal ordering even though the charge difference is zero. 2 The inorganic lattice of A 2 B I B III X 6 could be constructed by transmutation of two divalent metal ions (B II ) of a AB II X 3 single perovskite into one B I ion and one B III ion, i.e. 2B II → B I + B III .…”

Optoelectronic insights of lead-free layered halide perovskites

“… 67 In particular, the rock-salt-ordered double perovskite structure is stabilized by the J–T distortion, that splits the unequally occupied e g orbitals, and lowers the energy of the octahedral units. 68 In contrast to the electronic transition arising from the J–T distortion in Cu( ii ), with d 9 electronic configuration, there are two possible conditions when the J–T inactive Cu( i ) can display the electronic transitions. The first is the temporary oxidation of the d 10 system into d 9 configuration by photoexcitation.…”

Mapping Uncharted Lead-Free Halide Perovskites and Related Low-Dimensional Structures

“…This is the case in double perovskites (DPs) (elpasolites), in which this substitution occurs via having a + 1 and a + 3 charged central cation in halide octahedra alternating through the crystal structure, expressed by the A 2 MM ′ X 6 fixed stoichiometric formula (Figure 4a shows the crystal structure, Figure 4b marks ion M with B) [28]. There are examples of achieving stable rock-salt-ordered DP structures where both M and M ′ are divalent, but usually, these components rather form the stoichiometry of a simple perovskite with a disordered configuration, AM(II)M ′ (II)X 3 , due to the zero charge difference, as shown in Figure 4b [29]. Having a different order than the rock-salt arrangement by a couple of compositions with A 2 M(I)M(II)X 5 stoichiometry has also been reported [30].…”