Yu Chen1,2,Christopher Bartel1,2,Maxim Avdeev3,Ya-Qian Zhang1,2,Huiwen Ji4,Gerbrand Ceder1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Australian Nuclear Science and Technology Organisation3,The University of Utah4
Yu Chen1,2,Christopher Bartel1,2,Maxim Avdeev3,Ya-Qian Zhang1,2,Huiwen Ji4,Gerbrand Ceder1,2
University of California, Berkeley1,Lawrence Berkeley National Laboratory2,Australian Nuclear Science and Technology Organisation3,The University of Utah4
Rechargeable batteries based on multivalent working ions are promising candidates for next-generation high-energy-density batteries. Development of these technologies, however, is largely limited by the low diffusion rate of multivalent ions in solid-state materials, thereby necessitating a better understanding of the design principles that control multivalent-ion mobility. Here, we report Ca<sub>1.5</sub>Ba<sub>0.5</sub>Si<sub>5</sub>O<sub>3</sub>N<sub>6</sub> as a potential calcium solid-state conductor and investigate its Ca migration mechanism by means of ab-initio computations and neutron diffraction. This compound contains partially occupied Ca sites in close proximity to each other, providing a unique mechanism for Ca migration. Nuclear density maps obtained with the maximum entropy method from neutron powder diffraction data provide strong evidence for low-energy percolating one-dimensional pathways for Ca-ion migration. Ab initio molecular dynamics simulations further support a low Ca-ion migration barrier of ~400 meV when Ca vacancies are present and reveal a unique “vacancy-adjacent” concerted ion migration mechanism.