A tetragonal polymorph of SrMn2P2 made under high pressure - theory and experiment in harmony

Following the predictions of total energy calculations, a tetragonal SrMn 2 P 2 phase is proposed and successfully formed under high pressure. At ambient pressure, SrMn 2 P 2 adopts the primitive trigonal La 2 O 3 structure type (space group P 3&cmb.macr; m 1). However, the results of total energy calculations indicate that SrMn 2 P 2 should be more stable in the tetragonal ThCr 2 Si 2 structure type (space group I 4/ mmm ) than in its known trigonal structure, thus motivating our synthetic experiments. Guided by these calculations, a new tetragonal polymorph of SrMn 2 P 2 was found under the relatively mild conditions of 5 GPa applied pressure at a temperature of 900 °C through the transformation of the ambient pressure trigonal form. The new polymorph has the body centered tetragonal ThCr 2 Si 2 structure type, as predicted. The electronic structure calculations indicate the likelihood of antiferromagnetic, semiconducting properties for the high pressure SrMn 2 P 2 phase. A trigonal-tetragonal phase transition in SrMn 2 P 2 is proposed and confirmed experimentally under high pressure. At ambient pressure, SrMn 2 P 2 crystallizes in the primitive trigonal La 2 O 3 structure type (space group P 3&cmb.macr; m 1) in blue. Under high pressure, the tetragonal ThCr 2 Si 2 structure type (space group I 4/ mmm ) in red is more stable.