High-Pressure Low-Temperature Study of CaO(BO) ( = Pr, Nd, Gd, Er, Tm).

We investigated the site-disorder and thermal expansion of O(BO) ( = Pr, Nd, Gd, Er, Tm) through a single crystal structural study conducted between 100 and 300 K. Additionally, a high-pressure synchrotron X-ray diffraction study at low temperatures was conducted to determine the compressibility of both ordered and disordered prototype oxyborate lanthanides, specifically NdCaO(BO) and ErCaO(BO). The study revealed distinct behaviors consistent with their respective ionic radii. Furthermore, satellite reflections at 50 K, along with the onset of a triple -parameter in the Nd crystal, indicate that the ground state of this extensively studied family may be different from what was previously reported.