Electron density topology of high-pressureBa8Si46from a combined Rietveld and maximum-entropy analysis

Pressure-induced electron topological transitions in Ba-doped Si clathrate

“…These observations suggest an increase in ionicity of the Si atoms by transfer of electrons from the Si site to the interstitial regions. 18,33 This finding is again consistent with the picture that Si atoms rehybridize 18,33 from sp 3 to spd. The participation of the Si 3d orbitals in chemical bonding allows a charge transfer from Si to the Ba atoms, slightly increasing the charge.…”

“…The onset of the structural transition is at 12.4 GPa and completed at 18.6 GPa. It is already known that the transition is the result of the rehybridization of the framework Si atoms, 18 and the RMC calculations show the Si atoms are likely positional disordered.…”

“…The powder diffraction patterns used previously for Rietveld refinements 8,18 were used in the RMC modeling. Experimental details have been reported in Refs.…”

High-pressure phase transformations, pressure-induced amorphization, and polyamorphic transition of the clathrateRb6.15Si46

“…64 Other recent results using a combined Rietveld and maximum-entropy approach to analyze the x-ray diffraction data suggest that the volume collapse transition of Ba 8 Si 46 could be associated with s-p-d rehybridization of the Si atoms at high pressure, leading to a weakening of the Si-Si bonds and a collapse of the unit-cell volume without changing the crystalline structure. 62 In this interpretation of Tse et al 62 ͑and also proposed by San Miguel et al 30 ͒, the volume collapse can be traced to an electronic topological transition involving a substantial rearrangement of the valence electron distribution accompanied by positional disordering in the Si sites. The Si-Si bonding electrons are removed from the bonding region leading to the weakening of the Si-Si bonds, resulting in a displacive but isostructural phase transition taking place with a large volume reduction.…”

“…5,27-31 These anomalies in the V͑P͒ relations most likely correspond to an unusual type of symmetry-conserving phase transition. 5 Various explanations for the transition have been proposed, including the presence of electronic 30,62 or phonon instabilities, 28 or possibly vacancy formation on the framework silicon sublattice. 63 X-ray absorption studies on Ba 8 Si 46 show a discontinuity in the Ba K-edge position that could indicate a change in electronic structure at the transition.…”