Metastable Layered Cobalt Chalcogenides from Topochemical Deintercalation

Abstract

We present a general strategy to synthesize metastable layered materials via topochemical deintercalation of thermodynamically stable phases. Through kinetic control of the deintercalation reaction, we have prepared two hypothesized metastable compounds, CoSe and CoS, with the anti-PbO type structure from the starting compounds KCoSe and KCoS, respectively. Thermal stability, crystal structure from X-ray and neutron diffraction, magnetic susceptibility, magnetization, and electrical resistivity are studied for these new layered chalcogenides; both CoSe and CoS are found to be weak itinerant ferromagnets with Curie temperatures close to 10 K. Due to the weak van der Waals forces between the layers, CoSe is found to be a suitable host for further intercalation of guest species such as Li-ethylenediamine. From first-principles calculations, we explain why the Co chalcogenides are ferromagnets instead of superconductors as in their iron analogues. Bonding analysis of the calculated electronic density of states both explains their phase stability and predicts the limits of our deintercalation technique. Our results have broad implications for the rational design of new two-dimensional building blocks for functional materials.

Frustrated magnetism in the tetragonal CoSe analog of superconducting FeSe

“…Single crystals and powders of CoSe were synthesized following the previous method in literature. 10 Crystals of CoSe were lustrous silver with high degree of layered morphology.…”

“…We can rule out superparamagnetism as a possible explanation as we have observed remanent magnetization and magnetic hysteresis for CoSe which would not occur in a superparamagnetic material. 10 In order to observe the glassy character in CoSe, we performed AC magnetic susceptibility measurements to probe the time-dependence of the magnetization around the transition temperature.…”

“…Previously, we have overcome this challenge by topochemical means to convert KFe 2 S 2 to superconducting FeS. 9 Using a similar method, we successfully prepared two new FeCh analogues, tetragonal CoSe and CoS. 10 The ferromagnetic ordering from 78 K in KCo 2 Se 2 11 to 10 K in CoSe 10 was suppressed by de-intercalation of potassium cations to form pure CoSe as shown in Figure 1. These new Co-based phases are promising for understanding the Fe-based superconductors due to their structural and electronic proximity.…”

Structure‐Selective Cation Exchange in the Synthesis of Zincblende MnS and CoS Nanocrystals

“…A foundational goal of materials synthesis is the ability to predictably access atargeted crystal structure,asthe arrangements and coordination environments of the constituent atoms help to define its properties.I ti se specially important to identify synthetic pathways that lead to the formation of crystal structures that are metastable in bulk systems,a nd therefore not typically accessible.S uch synthetic strategies make it possible to avoid undesired phases that most readily form while instead favoring the formation of alternate phases of the same composition. Fore xample,s olid-state metathesis, [1][2][3] topotactic transformations, [4][5][6] epitaxial thin film formation, [7][8][9] and solvothermal precipitation methods [10][11][12][13][14][15] have succeeded in producing phases having crystal structures that cannot be accessed directly through traditional high temperature reactions.…”

Structure‐Selective Cation Exchange in the Synthesis of Zincblende MnS and CoS Nanocrystals

“…Fore xample,s olid-state metathesis, [1][2][3] topotactic transformations, [4][5][6] epitaxial thin film formation, [7][8][9] and solvothermal precipitation methods [10][11][12][13][14][15] have succeeded in producing phases having crystal structures that cannot be accessed directly through traditional high temperature reactions. Fore xample,s olid-state metathesis, [1][2][3] topotactic transformations, [4][5][6] epitaxial thin film formation, [7][8][9] and solvothermal precipitation methods [10][11][12][13][14][15] have succeeded in producing phases having crystal structures that cannot be accessed directly through traditional high temperature reactions.…”