Pressure-induced semiconductor-to-metal phase transition of a charge-ordered indium halide perovskite

Abstract

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In+/In3+) inorganic halide perovskite with the composition of Cs2In(I)In(III)Cl6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

The underappreciated lone pair in halide perovskites underpins their unusual properties

“…Instead of a single bonding Pb 6s-Br 4p band centered roughly around -7.5 eV, we see two corresponding bands centered roughly around -5 eV (Tl) and -10.5 eV (Bi), reflecting the relative stability of the lone-pair s orbitals of the isolated cations, which increases in the order In [23][24][25] While stoichiometric "Cs 2 TlBiBr 6 " has not been realized, (MA) 2 TlBiBr 6 has been prepared, and exhibits a bandgap of ∼2.2 eV. 26 Unfortunately, Tl + is exceedingly toxic (and appears too large to form a stable Cs-compound at full occupancy), and halides of In + tend to be unstable against further oxidation or disproportionation to In 0 and In 3+ 27-29 and prone to severe lone-pair-driven distortions, which reduce orbital overlap and change connectivity, [28][29][30] seemingly rendering halide double perovskites that are electronically equivalent to lead halide single perovskites practically out of reach.…”

The effects of strain and charge doping on the electronic properties of graphitic C3N5

“…The semiconductor-to-metal transition can have a range of potential applications in electrochromic devices, field effect transistors, sensors, memory devices, and switch devices. [32][33][34][35] These detailed investigations can lay excellent theoretical foundations for the future applications of g-C 3 N 5 in electronics.…”

Strain Engineering of Metal Halide Perovskites on Coupling Anisotropic Behaviors

“…[ 42 ] The metallization of Cs 2 In(I)In(III)Cl 6 SCs has been ascribed to the electronic delocalization of In + and In 3+ centers. [ 41 ] As the MHPs used in high‐pressure tests are generally polycrystalline, their anisotropic nature results in variable A and B values (see Table 2 ). These MHPs recover their original crystalline structures with/without partially distorted polyhedra upon decompression.…”

“…All experimental data are extracted from refs. [ 34–37,40–42,49,51,52,55,57,58,60,61,63–66,68,70,72,74,80,82,84,87–92,96–100 ] .…”

“…Note that the stress generated in MHPs during high‐pressure tests ranges from a few GPa to dozens of GPa, [ 34–37 ] whereas the in‐service stress does not exceed a few hundreds of MPa. [ 38,39 ] The corresponding bandgap may decrease to zero due to perovskite metallization during laboratory experiments [ 34,40–42 ] while the in‐service bandgap evolution is much less pronounced. For instance, the bandgap value of 2D (CH 3 (CH 2 ) 3 NH 3 ) 2 (CH 3 −NH 3 ) n−1 Pb n I 3n+1 increased by ≈13.3 meV/% (meV per percent strain) at a strain level of 0–1.2%.…”