Pressure-induced volume collapse in PbCrO$_{3 }$-- a combined experimental and theoretical investigation

PbCrO$_{3}$ in perovskite structure surprisingly has a larger volume (a $\sim $ 4.0 {\AA} ) [1, 2] compared to PbTiO$_{3 }$(a $\sim $ 3.95 {\AA}). We synthesized a powder sample of PbCrO$_{3}$ and performed x-ray diffraction studies in a diamond anvil cell up to $\sim $ 30GPa. Our experiments show a pressure induced volume collapse at 1.6GPa by $\sim $9.8{\%}. To investigate its origin we performed DFT computations with LDA+U and GGA+U using ABINIT, relaxing the strain and the internal coordinates, for different distorted perovskite phases and spin configurations. We identified the volume collapse with the high pressure phase being cubic and the low-pressure phase being tetragonal and non-centrosymmetric. The spin-configuration is G-AFM with a local moment of $\sim $ 2.2$\mu _{B}$, comparable to experiments [1]. No spin or metal-insulator transition is observed in our computations. Rather, orbital ordering stabilizes the low pressure phase. Computations show the bulk moduli of the two phases to be very different, consistent with our experiments. Both phases are metallic. [1] W. L. Roth \textit{et.al}., J. Appl. Phys. \textbf{38}, 951 (1967), [2] Angel M. Arivalo-Lopez \textit{et.al}., J. Solid State Chemistry \textbf{180}, 3271 (2007)