In situ high-temperature structural evolution of the Ca(Ti,Ge)O3 perovskite solid solution: looking for a new locked-tilt perovskite

A recent synchrotron structural investigation at high-pressure (HP) sets YAl0.25Cr0.75O3 orthorhombic perovskite as the prototype of the so-called "locked-tilt" perovskites. Placed at the boundary of the previously described structural evolution models for GdFeO3-type perovskites at HP, YAl0.25Cr0.75O3 represents the first finding of a perovskite characterized by the absence of changes in the octahedral tilting (as well as octahedral distortion), and a volume reduction with P exclusively controlled by an isotropic polyhedral compression. Although a theoretical modeling of a new locked-tilt perovskite can be done with a high degree of accuracy, the only way to confirm the possible occurrence of a perovskite belonging to this family is through new experiments at non-ambient conditions (HP or High Temperature, HT). The use of geochemical constrains, and the assessment of the "normalized cell distortion factor with pressure/temperature, dnorm(P/T)" for several perovskite solid solutions, allowed the identification of three possible locked-tilt perovskite formulations, i.e., La(Mn0.69Ga0.31)O3, Ca(Ti0.95Ge0.05)O3, and (Sc0.86Y0.14)AlO3, respectively. The aim of our proposal is to investigate at HT the above identified Ca(Ti,Ge)O3 perovskite solid solution which were previously characterized at ambient conditions through structural refinements from X-ray Powder Diffraction (XRPD). Besides to extend the locked-tilt perovskite family, this investigation will provide a deeper comprehension on the role of these compounds in view of their application as functional materials (e.g., multiferroics, layered perovskites). Furthermore, the structural modification at HT of a hypothesized locked-tilt perovskite where the cubic site has a lower formal charge than the octahedral site (i.e., the 2:4 Ca(Ti0.95Ge0.05)O3), will be extremely useful from a geophysical viewpoint to outline a more accurate Earth's mantle model.

Progetto accettato dal Sincrotrone Elettra di Trieste, per la quale sono stati conferiti 6 giorni (144 ore) di accesso alla struttura per degli esperimenti. Il budget totale stimato del progetto è di 79500 € (mediamente vengono stimati 550€/h) compresi i vari rimborsi.