Mapping Pressure- and Temperature-Induced Structural and Magnetic Transitions in Perovskite PrNiO₃ with Local and Long-Range Probes

The RNiO3 nickelate perovskites represent a promising class of materials for spintronics applications such as in modern communication devices. This is related to the large diversity of properties shown by these compounds. Indeed, depending on the external parameters, such as temperature, pressure, or R cation size, they can exhibit para- or antiferromagnetic behavior and can transform from an insulator to a metal. Among them, PrNiO3 is one of the most important members because it exhibits tunable electronic and magnetic properties. However, our understanding of how these properties can be modified through external parameters, such as pressure and temperature, remains under debate. In this work, we characterized the structural, electronic, and magnetic properties of PrNiO3 in the range of 0-21 GPa and 10-973 K. For this purpose, we performed synchrotron X-ray diffraction (SXRD), X-ray absorption near-edge structure spectroscopy (XANES), and magnetic measurements. We compared the experimental XANES data with ab initio calculations to extract information about the electronic structure. The diffraction data demonstrated a sharp transition at the bulk level between monoclinic and orthorhombic PrNiO3 (P2(1)/n -> Pbnm) at T-IM similar to 130 K, while XANES data, which probe the medium-range and electronic structure, showed progressive changes between 90 and 130 K. The latter is in accordance with our previous EXAFS data, attesting that this transition occurs around 130 K and that it is driven at the local and medium-range scales. Between 700 and 800 K at ambient pressure, the Pbnm phase transforms into a rhombohedral phase (R3c), in agreement with a previous laboratory X-ray diffraction study. Our XANES data and ab initio simulations across this transition indicate a significant raising of the orbital overlap between Ni 3d and O 2p, suggesting superior electronic properties of the rhombohedral phase compared to the orthorhombic structure. Under isothermal cold compression, we found that the Pbnm to R3c transition is characterized by a large coexisting domain between 5.8 and 12.2 GPa. Based on the present and literature data, we proposed an extended pressure- and temperature-phase diagram of PrNiO3 and provided first-order constraints on the interplay between external parameters and properties in nickelates.