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

Following the predictions of total energy calculations, a tetragonal SrMn₂P₂ phase is proposed and successfully formed under high pressure. At ambient pressure, SrMn₂P₂ adopts the primitive trigonal La₂O₃ structure type (space group P3m1). However, the results of total energy calculations indicate that SrMn₂P₂ should be more stable in the tetragonal ThCr₂Si₂ structure type (space group I4/mmm) than in its known trigonal structure, thus motivating our synthetic experiments. Guided by these calculations, a new tetragonal polymorph of SrMn₂P₂ 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 ThCr₂Si₂ structure type, as predicted. The electronic structure calculations indicate the likelihood of antiferromagnetic, semiconducting properties for the high pressure SrMn₂P₂ phase.