Pressure-Induced Phase Transitions in Bilayer La$_3$Ni$_2$O$_7$

TL;DR

This study investigates pressure-induced structural phase transitions and electronic behavior in bilayer La$_3$Ni$_2$O$_7$, revealing a symmetry change and complex phase diagram under high pressure conditions.

Contribution

It reports the growth of single crystals and detailed structural and electronic phase analysis of La$_3$Ni$_2$O$_7$ under high pressure, highlighting new pressure-induced phase transitions.

Findings

Structural transition from orthorhombic to tetragonal near 12 GPa.

Pressure and field-dependent resistance measurements up to 27.4 GPa.

Construction of a pressure-temperature phase diagram.

Abstract

La$_3$Ni$_2$O$_7$ exists in two polymorphs: an unconventional structure with alternating layers of single- and triple-layered nickel-oxygen octahedra, and a classical double-layered Ruddlesden-Popper phase. In this study, we report the growth of single crystals of classical double-layered La$_3$Ni$_2$O$_7$ using the floating zone method. Structural characterization under pressures up to 15.4 GPa reveals a gradual transition from orthorhombic to tetragonal symmetry near 12 GPa. Additionally, we present pressure and field-dependent electrical resistance measurements under pressures as high as 27.4 GPa, from which we construct a phase diagram.