Evidence of Athermal Metastable Phase in a Halide Perovskite: Optically Tracked Thermal-Breach Memory

TL;DR

This study reveals that methylammonium lead iodide exhibits an athermal metastable phase with optically detectable thermal-breach memory, enabling precise temperature stability monitoring for applications like package tagging.

Contribution

It demonstrates the existence of an athermal metastable phase in halide perovskites and introduces an optical method to record thermal breaches with high sensitivity.

Findings

Metastable phase is athermal with minimal temporal evolution.

Multiple metastable states can be prepared via different thermal pathways.

Optical luminescence reliably records breaches in temperature stability.

Abstract

Halide perovskite materials have been extensively studied in the last decade because of their impressive optoelectronic properties. However, their one characteristic that is uncommon for semiconductors is that many undergo thermally induced structural phase transitions. The transition is hysteretic, with the hysteresis window marking the boundary of the metastable phase. We have discovered that in methylammonium lead iodide, this hysteretic metastable phase is athermal, meaning it shows almost no temporal phase evolution under isothermal conditions. We also show that a large number of distinguishable metastable states can be prepared following different thermal pathways. Furthermore, under a reversible thermal perturbation, the states in the metastable phase either show return-point memory or undergo a systematic nonrecoverable phase evolution, depending on the thermal history and the sign of the temperature perturbation. Since the phase fraction can be probed with extreme sensitivity via luminescence, we have an optically retrievable memory that reliably records any breach in temperature stability. Such thermal-breach memory in athermal martensites, of which there are numerous examples, may be useful for tagging packages requiring strict temperature control during transportation or preservation.