First principles study and comparison of vibrational and thermodynamic properties of XBi(X=In,Ga,B,Al)

In the present work, vibrational and thermodynamic properties of XBi（X = B, Al, Ga, In） compounds are compared and investigated. The calculation is carried out using density functional theory（DFT） within the generalized gradient approximation（GGA） in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory（DFPT） as implemented in Quantum ESPRESSO（QE） code. Thermodynamic properties involving phonon density of states（DOS） and specific heat at constant volume are investigated using quasiharmonic approximation（QHA） package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm^-1, 150 cm^-1, 300 cm^-1, and 150 cm^-1, respectively. For all compounds,the three acoustic modes near the gamma point have a linear behavior. C_V is a function of T-3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected.

Doping Mn into(Li_(1-x)Fe_x)OHFe_(1-y)Se superconducting crystals via ion-exchange and ion-release/introduction syntheses

We report the success in introducing Mn into（Li1-xFex）OHFe1-y Se superconducting crystals by applying two different hydrothermal routes, ion exchange（1-step） and ion release/introduction（2-step）. The micro-region x-ray diffraction and energy dispersive x-ray spectroscopy analyses indicate that Mn has been doped into the lattice, and its content in the 1-step fabricated sample is higher than that in the 2-step one. Magnetic susceptibility and electric transport properties reveal that Mn doping influences little on the superconducting transition, regardless of 1-step or 2-step routes. By contrast, the characteristic temperature T^＊, at which the negative Hall coefficient reaches its minimum, is significantly reduced by Mn doping.This implies that the hole carriers contribution is obviously modified, and hence the hole band might have no direct relationship with the superconductivity in（Li1-xFex）OHFe1-y Se superconductors. Our present hydrothermal methods of ion exchange and ion release/introduction provide an efficient way for elements substitution/doping into（Li1-xFex）OHFe1-y Se superconductors, which will promote the in-depth investigations on the role of multiple electron and hole bands and their interplay with the high-temperature superconductivity in the FeSe-based superconductors.