Local distortions and orbital disorder in ultra-high A-site variance perovskite Ce0.5Ba0.5MnO3

Perovskites are highly sensitive to their chemical compositions, and particularly the cation distribution on the A-site strongly affects their properties. The conventional control parameters involving charge doping and perovskite tolerance factor are often the primary ones considered for tuning structure and property. However, chemical disorder at the A-site, characterised by the variance associated with the average size (ionic radii) of the cation, also have a profound effect. Recently we have prepared via high pressure synthesis Ce(IV)0.5Ba(II)0.5Mn(III)O3, which has the highest reported A-site variance of any known perovskite. While the system appears cubic and highly crystalline (very low microstrain), broad diffuse features in the neutron powder diffraction data, and microscopy results, indicate the presence of order across ~ 5nm length scales, locally possessing Pbnm symmetry and hence potentially exhibiting c-type orbital ordering. The relationship between the “pseudo cubic state”, orbital-disorder transitions in La(III)Mn(III)O3, and the occurrences of colossal magnetoresistance on hole doping, have been widely discussed in the literature. Ce0.5Ba0.5MnO3 which exhibits such a pseudo cubic state from 2 K to room temperature thus provides an ideal prototype system for exploring this interplay between chemical and orbital disorder, which we propose to investigate via a total scattering experiment on POLARIS.