Missing superconductivity in BaAlSi with the AlB2 type structure

A series of BaAl2−xSixH2−x (0.4<x<1.6) hydrides with compositions and structures in between BaSi2 and BaAl2H2

“…The c-axis is relatively independent of x. These trends were also reported by Yamanaka et al [12]. For the BaAlSi (x = 1) phase, the cell parameter could be indexed with a = 4.2989(6) Å and c = 5.1437(7) Å in good agreement with the previously reported BaAlSi, a = 4.290 Å and c = 5.140 Å [13].…”

“…The BaAlSi, precursor material of BaAlSiH, itself is interesting. Recently, Yamanaka et al reported a superconductor transition with T c = 2.8 K in the BaAlSi system [12]; they revealed that Al/Si ratio in BaAlSi is changeable according to BaAl 2−x Si x (1 < x < 1.5). However, superconductivity was only observed for x > 1.…”

Crystal structure, electronic structure, and vibrational properties ofMAlSiH(M=Ca,Sr,Ba)<

“…2 In this respect the ternary silicides MAlSi ͑M =Ca,Sr,Ba͒ have shown interesting behavior. [3][4][5][6][7][8] Here Al and Si atoms are commonly distributed over the site of the boron atoms forming hexagon layers and M atoms occupy the "intercalating" position. For CaAlSi and SrAlSi the superconducting temperatures T c are 7.8 and 5.1 K, respectively, while, remarkably, stoichiometric BaAlSi is not a superconductor above 2 K, but slightly silicon-rich, BaAl 0.95 Si 1.05 ͑T c = 2.8 K͒.…”

“…Obviously the M component has a strong influence on T c , which has been empirically related to changes in the hexagonal c / a ratio of the AlB 2 structure. 8 The detailed crystal structure of MAlSi, however, is still discussed because of the difficult discrimination of Al and Si atoms from diffraction experiments. The disordered AlB 2 structure ͑space group P6 / mmm͒ has been disputed in favor of the SrPtSb structure ͑space group P6m2͒ where Al and Si atoms are ordered alternately in the planar hexagon layers.…”

Electronic structures and lattice dynamics of ternary intermetallic compounds MAlSi (M = Ca, Sr, Ba) at high pressures: A first-principles study

“…The electronic structure, the phonon dispersion spectrum and the electron-phonon interaction in the MAlSi (M = Ca, Sr, Ba) compounds have been calculated using the full-potential, density-functional-based method [16][17][18], and the superconductivity of MAlSi has also been discussed [19,20]. The lattice dynamical properties and electron-phonon coupling in CaAlSi have also been investigated by combining inelastic Xray scattering experiments with ab initio calculations [21].…”