Lithium nickel borides: evolution of [NiB] layers driven by Li pressure

Abstract

Here we show the effect of Li chemical pressure on the structure of layered polymorphs with LiNiB composition: RT-LiNiB (room temperature polymorph) and HT-LiNiB (high temperature polymorph), resulting in stabilization of the novel RT-Li_1+xNiB (x ∼ 0.17) and HT-Li_1+yNiB (y ∼ 0.06) phases. Depending on the synthesis temperature and initial Li content, precisely controlled via hydride route synthesis, [NiB] layers undergo structural deformations, allowing for extra Li atoms to be accommodated between the layers. In situ variable temperature synchrotron and time-dependent laboratory powder X-ray diffraction studies suggest Li step-wise deintercalation processes: RT-Li_1+xNiB → RT-LiNiB (high temp.) → LiNi₃B_1.8 → binary Ni borides and HT-Li_1+yNiB → HT-LiNiB (high temp.) → LiNi₃B_1.8 → binary Ni borides. Quantum chemistry calculations and solid state ⁷Li and ¹¹B NMR spectroscopy shed light on the complexity of real superstructures of these compounds determined from high resolution synchrotron powder diffraction data.