Search for polyhydrides in the Mn-H system up to 150 GPa and observation of MnH7

The aim of the present proposal is to study the gradual uptake of hydrogen by manganese and to synthesize the predicted MnH7 [5]. This superhydride structure is remarkable by having a mixed H sublattice, with one hydrogen being under the molecular form and the other ones under an atomic form. By measuring the excess volume per H atom from the compression curve, we will question if MnH7 can be considered an additive-volume alloy of Mn and metal H, as for all other superhydrides [6]. Finally, we will investigate if nuclear quantum effects can change the sequence of the MnHx compounds stable under pressure: in particular, cal-culations predict that MnH4 is stable but probably not MnD4 [5].