Delving into the Discrepancy of Phase Developments between Powder and Shaped Pellets of BaCO3

Although renewed scientific interest has emerged in BaCO3 based on its stable orthorhombic (Pmcn) configuration, the present work examines a severe instability for the same when BaCO3 is heat-treated in pelletized form in the vicinity of its phase transformation (from orthorhombic to trigonal phase) temperature. Although the calcined powders of BaCO3 conform well to the standard JCPDS files, the BaCO3 pellets depicted either a strong preferential c-axis orientation or strange variations in the intensity ratios of the peaks when characterized via X-ray diffraction and Raman spectroscopy. Our analysis involving a thermo-shape factor (xi) attempts to connect between the ease/difficulty of energy release during trigonal to orthorhombic phase transformation. Our results also suggest that an easy compressible Ba-O atomic arrangement along the c-axis paved the path for the orientation perpendicular to the (002) plane. While the phase transformations in relation to pressure and/or temperature is well-known, our results suggest that the dependence of such phase changes with shaping/consolidation may also need relevant attention (wherever applicable) for future scientific understanding.

Automated summary

This study investigates the instability of BaCO3 in pelletized form during heat treatment near its phase transformation temperature. The results show that BaCO3 pellets exhibit either a strong preferential c-axis orientation or strange variations in the intensity ratios of the peaks. The analysis suggests that the ease/difficulty of energy release during the phase transformation is related to the compressibility of the Ba-O atomic arrangement along the c-axis. The findings highlight the importance of considering the dependence of phase changes on shaping/consolidation for future scientific understanding.