Novel High Pressure Structures and Superconductivity ofCaLi2

Abstract

Using evolutionary methodology for crystal structure prediction, we explore high-pressure phases of CaLi2, a compound made of two elements that show anomalies upon compression. In addition to the known low-pressure Laves phases, we find two novel structures with space groups C2/c and P2{1}/c, stable at pressure ranges of 35-54 GPa and 54-105 GPa, respectively. It is found that decomposition into pure elements is energetically favorable at pressures of 20-35 GPa and above 105 GPa. Such decomposition-recombination-decomposition oscillating behavior with pressure is predicted for the first time in a binary compound. The C2/c and P2{1}/c phases are predicted to be superconductors, and the calculated T{c} of approximately 15 K at 45 GPa is in good agreement with experiment.

Superconducting high-pressure phase of platinum hydride from first principles

“…The calculated Eliashberg phonon spectral function α 2 F(ω), logarithmic average phonon frequency ω log , and the EPC strength λ at different pressures are listed in Table II. The superconducting temperature T c could be estimated from the Allen-Dynes modified McMillan equation, by using 24 For estimating T c , the following parameters are used: a typical value of Coulomb pseudopotential µ * = 0.1 (for most materials, µ * takes values between 0.10 − 0.14 and the associated uncertainty on T c is usually ∼15 − 20%), 7,10,25,26 a calculated λ = 0.85 at 113 GPa (which indicates the strong EPC), and a calculated ω log = 328.66 K. Thus, we predict T c = 17.2 K, which is in good agreement with experimental result T c = 17 K. 14 At 113 GPa, the heavy Pt atoms dominate the low-frequency vibrations, while the light H atoms contribute significantly to the high-frequency modes [see the dotted line in Fig. 4(b)].…”

Novel superconducting skutterudite-type phosphorus nitride at high pressure from first-principles calculations

“…New theoretical structure prediction techniques6789 have been used to identify novel superconductors by applying pressure to stoichiometries that form phases without the properties of superconductivity, metallicity or even stability at atmospheric pressure101112131415. In spite of their great potential, nitride-based materials remain relatively unexplored due to the high stability of nitrogen molecules at ambient pressure; the strong N≡N triple bond results in a high kinetic barrier to polymerisation, thus extreme temperatures and pressures are required to synthesise many nitrides.…”

Novel magnesium borides and their superconductivity

“…Here we used µ * = 0.10 for Coulomb's pseudopotential, as a reasonable value for most materials [55][56][57] . After MgB 2 , C2/m-MgB 4 has the highest T c of 2.8 K at zero pressure (it is metastable at 0 GPa).…”

“…Bands structures and total DOS of other sandwich borides are also provided in the ESI, Fig. S3, S6 and S10)The critical temperature of superconductivity is estimated from the Allen-Dynes modified McMillan equation 54 :where ω log is the logarithmic average phonon frequency and µ * is the Coulomb pseudopotential,The EPC parameter λ is defined as integral involving the spectral function α 2 F :Here we used µ * = 0.10 for Coulomb's pseudopotential, as a reasonable value for most materials [55][56][57] . After MgB 2 , C2/m-MgB 4 has the highest T c of 2.8 K at zero pressure (it is metastable at 0 GPa).…”