Experimental and theoretical study of the phase transition between perovskite polytypes of BaPtO 3 under high pressure and temperature

APtO3 (A = Ca, Sr, Ba) is a unique family in the complex transition metal oxides with the AMO3 formula. Most 3⁢ and 4⁢AMO3 compounds adopt the perovskite structure when synthesized at ambient or high pressure; however, APtO3 perovskites have not been reported, even if their geometric tolerance factor, , falls in the range suitable for the perovskite structure. Herein, we studied the crystal structures of BaPtO3 by performing the in situ x-ray diffraction over a broad range in the pressure ()–temperature () phase diagram. The perovskite BaPtO3 can be stabilized at >35 GPa and >1100 K. A variety of crystal structures, including the perovskite structure and its hexagonal polytypes, observed in the – phase diagram of BaPtO3 match the structure predictions from the first-principles calculations reasonably well.