Pressure/temperature/substitution-induced melting of A-site charge disproportionation in Bi_(1-x)La_(x)NiO_3 (0 =< x =< 0.5)

TL;DR

This study investigates how pressure, temperature, and La substitution induce a structural and electronic transition in Bi1-xLaxNiO3, revealing a universal ligand-hole mechanism in ANiO3 compounds.

Contribution

It demonstrates that external stimuli cause melting of A-site charge disproportionation, unifying the understanding of metal-insulator transitions in BiNiO3 and related compounds.

Findings

Pressure, temperature, and La substitution induce structural transitions.

Metallic phase characterized by ligand-hole state.

Universal ligand-hole dynamics in ANiO3 series.

Abstract

Metal-insulator transitions strongly coupled with lattice were found in Bi1-xLaxNiO3. Synchrotron X-ray powder diffraction revealed that pressure (P ~ 3 GPa, T = 300 K), temperature (T ~ 340 K, x = 0.05), and La-substitution (x ~ 0.075, T = 300 K) caused the similar structural change from a triclinic (insulating) to an orthorhombic (metallic) symmetry, suggesting melting of the A-site charge disproportionation. Comparing crystal structure and physical properties with the other ANiO3 series, an electronic state of the metallic phase can be described as [A3+Ld, Ni2+L1-d], where a ligand-hole L contributes to a conductivity. We depicted a schematic P-T phase diagram of BiNiO3 including a critical point (3 GPa, 300 K) and an inhomogeneous region, which implies universality of ligand-hole dynamics in ANiO3 (A = Bi, Pr, Nd,...).