Computationally Driven Discovery of a Family of Layered LiNiB Polymorphs

Abstract

Tw on ovel lithium nickel boride polymorphs,R T-LiNiB and HT-LiNiB,w ith layered crystal structures are reported. This family of compounds was theoretically predicted by using the adaptive genetic algorithm (AGA) and subsequently synthesized by ahydride route with LiH as the lithium source.U nique among the knownt ernary transition-metal borides,the LiNiB structures feature Li layers alternating with nearly planar [NiB] layers composed of Ni hexagonal rings with aB -B pair at the center.Acomprehensive study using ac ombination of single crystal/synchrotron powder X-ray diffraction, solid-state 7 Li and 11 BNMR spectroscopy, scanning transmission electron microscopy, quantum-chemical calculations,a nd magnetism has shed light on the intrinsic features of these polymorphic compounds.The unique layered structures of LiNiB compounds make them ultimate precursors for exfoliation studies,t hus paving aw ay toward twodimensional transition-metal borides,MBenes.

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

“…1). A structural relationship between the RT-LiNiB and HT-LiNiB polymorphs, Li-depleted phase LiNi 3 B 1.8 , Ni 2 B, and Li has been found, 11 indicating on the  [NiB] framework evolves with the changing of Li content and/or temperature variation ( Fig. S1).…”

“…In our recent study, 11 the Li-Ni-B ternary system was evaluated using an adaptive genetic algorithm (AGA) search for potentially stable ternary phases. As a result, a RT-LiNiB compound with a unique layered structure was computationally predicted and further synthesized experimentally using the hydride route.…”

“…Previously we showed 10,11 the hydride route is feasible for preparation of ternary lithium nickel borides providing fast reactions and accurate compositional control. The experimentally determined, LiH:Ni:B = 1.3:1:1.15, molar ratio results in phase-pure samples of LiNiB phases with minimal excess of LiH and B needed.…”

“…This way, two lithium nickel boride polymorphs RT-LiNiB (room temperature polymorph) and HT-LiNiB (high temperature polymorph), with unique layered crystal structures, were discovered. 11 In these polymorphic compounds, Li layers, featuring hexagonal-like or squared motif, alternate with nearly planar [NiB] layers, whose structure differs depending on the polymorph (Fig. 1).…”

“…Secondly, due to the unique arrangement of Li and [NiB] layers in their structures, exfoliation of these materials can open a pathway to novel two-dimensional (2D) nickel borides. 11,12 The search for 2D borides or MBene has been accelerated after successful preparation of the 2D transition metal carbides or MXene. 13,14 MXenes are extensively studied due to their attractive thermal, magnetic, mechanical and electric properties.…”