High Pressure/High Temperature synthesis of novel functional perovskites and their structural, magnetic, and electrical characterizations

This doctoral thesis explores the effective solid-state synthesis of novel functional perovskites under extreme High Pressure/High Temperature (HP/HT) conditions. Specifically, it presents a comprehensive investigation of BiCu0.5Mn0.5O3 (BCMO) and KPbFeMoO6 (KPFMO), illustrating how it is possible to manipulate the chemistry of the perovskite structures to finely tune their physical properties. BCMO is characterized by a disordered mesoscale distribution of the B cations and the correlation between magnetic and electrical properties has been pointed out. In particular, BCMO displays a weak FM-like transition at 320 K and a thermally activated electrical transport, while, in the low-temperature regime, the electrons’ localization on Mn site leads to a 3D Variable Range Hopping transport and an AFM spin-glassy state at 50 K. For KPFMO a reliable cubic structure has been proposed, while further investigations are required for cationic ordering evaluation. Contrarily to BCMO, it has a more resistive character, behaving as a dielectric below 250 K and showing an AFM transition at around 50 K. Thus, this study provides an in-depth analysis of the properties of these compounds, emphasizing structural characterizations through the combination of complementary techniques such as X-rays, electrons, and neutrons diffraction and highlighting the crucial role of the crystal structure resolution process. Additionally, the magnetic and electrical properties of these perovskites are explored and compared with those of similar compounds, highlighting the pros and cons of their behaviour as multifunctional materials.