Fig. 1: Phase transitions and lattice anchoring in CsPbI₃.

a CsPbI₃ crystal phases represented as a general function of temperature and octahedral tilting (indicated using curved arrows). Pb atoms are in black, I in red, and Cs in blue. b Illustration of anchoring imposed by a microgrid introduced into a thin film. c Initial position of a molecular dynamics (MD) simulation of a 4 x 4 x 4 supercell with I⁻ anions at the bottom (circled in red) restrained by a harmonic bias potential, V(d) = Kd², with d being the distance from their initial position and the K the strength of the restraint. d Probability distributions (grey) and averages (white) of all θ_z bond angles during the MD simulations as a function of K. The red line connecting the averages values is a guide for the eye. The effect of increasing K converges near 1000 kJ mol⁻¹ Å⁻², which is the typical order of magnitude of covalently bonded atoms.