Elastic and Electronic Properties of Superconducting CaPd2As2 and SrPd2As2 vs. Non-superconducting BaPd2As2

The first-principles calculations were performed to predict the elastic and electronic properties of the superconducting ThCr2Si2-type phases CaPd2As2 and SrPd2As2 in comparison with the non-superconducting CeMg2Si2-type phase BaPd2As2. Besides, the same properties were compared for CeMg2Si2- and ThCr2Si2-type polymorphs of BaPd2As2. We found that all these phases are mechanically stable and belong to soft materials with low hardness. The near-Fermi region is formed by the valence states of the blocks [Pd2As2] with decisive contributions of Pd 4d states. The values of N(E (F)) increase in the sequence: CaPd2As2 < SrPd2As2 < BaPd2As2, i.e. in the reverse sequence relative to the transition temperatures T (C). Thus, the change in T (C) cannot be explained by the electronic factor, i.e. by the simple correlation T N-C similar to(E (F)). Most likely the decrease in T (C) in the sequence CaPd2As2 -> SrPd2As2 and the absence of a superconducting transition in BaPd2As2 are related to the structural factors and the peculiarities of the electron-phonon coupling mechanism.