Path to high-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>T</mml:mi><mml:mi mathvariant="normal">c</mml:mi></mml:msub></mml:math> superconductivity via Rb substitution of guest metal atoms in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Sr</mml:mi><mml:msub><mml:mi mathvariant="normal">B</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> clathrate
Peiyu Zhang, Xue Li, Xin Yang, Hui Wang, Yansun Yao, Hanyu Liu
Abstract
Recently, a host-guest clathrate $\mathrm{Sr}{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ with $s{p}^{3}$-bonded boron-carbon framework was synthesized at $\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. Based on electron count, the structure is understood as guest ${\mathrm{Sr}}^{2+}$ cations intercalated in the ${({\mathrm{B}}_{3}{\mathrm{C}}_{3})}^{3\ensuremath{-}}$ framework. Previous calculations suggest that $\mathrm{Sr}{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ is a hole conductor with an estimated superconducting critical temperature $({T}_{\mathrm{c}})$ of 42 K at ambient pressure. If atoms with similar radius, such as Rb, can substitute ${\mathrm{Sr}}^{2+}$ in the lattice, the electronic as well as superconductivity properties of this material will be modified significantly. Here, we perform extensive simulations on the stability and physical properties of the Rb-Sr-${\mathrm{B}}_{3}{\mathrm{C}}_{3}$ system using first-principles density functional calculation in combination with cluster expansion and the calypso structure prediction method. We predict a phonon-mediated superconductor ${\mathrm{Rb}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ with a remarkably high ${T}_{\mathrm{c}}$ of 75 K at ambient pressure, which is a significant improvement from the estimated value (42 K) in $\mathrm{Sr}{\mathrm{B}}_{3}{\mathrm{C}}_{3}$. The current results suggest that substitution of alkali atoms in synthesized clathrate $\mathrm{Sr}{\mathrm{B}}_{3}{\mathrm{C}}_{3}$ is a viable route toward high-${T}_{\mathrm{c}}$ compounds.