Local Probing Naturally Layered Perovskites

• Auditório Abrahão de Moraes, no Instituto de Física;
• Transmissão pública: acompanhe pelo YouTube do IFUSP.
• Sala Zoom: Reunião 867 3090 4002 | Senha 378484
   

 

Naturally layered perovskite (NLP) phases such as the Ruddlesden-Popper (RP) presents an inspiring route to achieve unique magneto-electric, ferroelectric–photovoltaic or negative thermal expansion effects, among others. In these structures, the rotations of the disconnected perovskites octahedra can lead to different symmetry groups, polar and non-polar, and different magnetic orders adding extra pathways to engineer novel and efficient perovskites materials. Here, nanoscopic probing with local selective electrical and magnetic output information, is fundamental, as lattice distortions at the origin of the functional properties, not always show clear macroscopic signatures. Of particular interest is to understand how the individual lattice modes evolve across phase transitions and within a particular symmetry. This symmetry related fine details can be monitored via precise hyperfine Perturbed Angular Correlation γ-γ (PAC) measurements as we recently reported [1, 2]. In these NLP, specifically in Ca3-yCdyMn2-xTixO7, MnO6 octahedra rotation and tilting modes couple to polar cation displacement modes, inducing a ferroelectric polarization in a mechanism known as hybrid improper ferroelectricity [3-5]. Also, the negative thermal expansion observed in the lower dimension NLP, e.g. Ca2MnO4, is associated with a MnO6 antiphase rotation mode. PAC experiments performed in NPL paradigmatic examples in a wide temperature range and obtained at ISOLDE-CERN will be presented. The evolution of the electric field gradient, EFG, combined with ab-initio electronic structure calculations are presented to show the EFG sensibility to distinct MnO6  distortion modes and how it can inform about the local details that govern macroscopic effects.