Pressure/temperature/substitution-induced melting of A-site charge disproportionation in Bi1-xLaxNiO3 (0≤x≤0.5) -: art. no. 045104

Metal-insulator transitions strongly coupled with lattice were found in Bi1-xLaxNiO3. Synchrotron x-ray powder diffraction revealed that pressure (P similar to 3 GPa, T=300 K), temperature (T similar to 340 K, x=0.05), and La substitution (x similar to 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 ANiO(3) series, an electronic state of the metallic phase can be described as [A(3+)(L) under bar (delta), Ni2+(L) under bar (1-delta)], where a ligand-hole (L) under bar 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 ANiO(3) (A=Bi, Pr, Nd... ).