RESUMEN
From our material exploration study in wide pressure and temperature conditions, we found a new 6H polymorph of BaRhO3 was stabilised under high pressure conditions from 14 to 22 GPa. The material crystallised in the monoclinic 6H hexagonal perovskite structure in space group C2/c. The 4H BaRhO3 polymorph was stabilised at lower pressures, but the 3C cubic BaRhO3 likely requires pressures greater than 22 GPa. Both 6H and 4H polymorphs contain Rh2O9 dimers and the large 4d Rh orbital spatial diffusivity in these dimers leads to Pauli paramagnetic and metallic ground states, which are also supported by first-principles electronic structure calculations. High Wilson ratios of approximately 2 for either compound indicate strong electron correlation.
