Pressure-Driven Phase Evolution and Optoelectronic Properties of Lead-free Halide Perovskite Rb$_2$TeBr$_6$

TL;DR

This study explores how high pressure affects the structural, vibrational, and optical properties of Rb$_2$TeBr$_6$, revealing pressure-induced phase transitions and tunable optoelectronic characteristics.

Contribution

It provides new insights into pressure-driven phase evolution and optoelectronic property modulation in lead-free halide perovskite Rb$_2$TeBr$_6$.

Findings

PL intensity increases up to 2.4 GPa due to local structural reorientation.

Structural transitions occur at 8.0 GPa and above, leading to amorphization beyond 25.5 GPa.

Optical band gap narrows continuously under compression.

Abstract

The structural, vibrational, and optical properties of Rb$_2$TeBr$_6$ have been investigated under high pressure using synchrotron X-ray diffraction, Raman spectroscopy, photoluminescence (PL), and optical absorption measurements. At ambient conditions, Rb$_2$TeBr$_6$ crystallizes in the cubic Fm-3m structure, which remains stable below 8.0 GPa. Within this pressure range, subtle inter-octahedral rotations develop, producing a gradual localized deviation from the ideal cubic framework. This local reorientation facilitates radiative recombination, leading to a pronounced enhancement of PL intensity with pressure up to 2.4 GPa. Beyond this pressure point, enhancement of nonradiative relaxation channels result in gradual PL quenching. Additionally, the PL intensity increases upon the application of an external weak magnetic field. A structural transition to the orthorhombic Pnnm phase occurs at around 8.0 GPa, followed by a monoclinic P$2_1/m$ phase above 10.7 GPa, and eventual amorphization beyond 25.5 GPa. Optical absorption spectra reveal continuous band-gap narrowing upon compression. These findings demonstrate the strong coupling among lattice dynamics, electronic structure, and optical response in Rb$_2$TeBr$_6$, underscoring its potential as a pressure-tunable optoelectronic material