Polymorph Selectivity of Superconducting CuSe₂ Through Kinetic Control of Solid-State Metathesis

Abstract

Rational preparation of materials by design is a major goal of inorganic, solid-state, and materials chemists alike. Oftentimes, the use of nonmetallurgical reactions (e.g., chalcogenide fluxes, hydrothermal syntheses, and in this case solid-state metathesis) alters the thermodynamic driving force of the reaction and allows new, refractory, or otherwise energetically unfavorable materials to form under softer conditions. Taking this a step further, alteration of a metathesis reaction pathway can result in either the formation of the equilibrium marcasite polymorph (by stringent exclusion of air) or the kinetically controlled formation of the high-pressure pyrite polymorph of CuSe2 (by exposure to air). From analysis of the reaction coordinate with in situ synchrotron X-ray diffraction and pair distribution function analysis as well as differential scanning calorimetry, it is clear that the air-exposed reaction proceeds via slight, endothermic rearrangements of crystalline intermediates to form pyrite, which is attributed to partial solvation of the reaction from atmospheric humidity. In contrast, the air-free reaction proceeds via a significant exothermic process to form marcasite. Decoupling the formation of NaCl from the formation of CuSe2 enables kinetic control to be exercised over the resulting polymorph of these superconducting metal dichalcogenides.

Polymorphic Metastability in Colloidal Semiconductor Nanocrystals

“…Of the synthetic techniques employed to generate metastable polymorphs of semiconductor nanocrystals, cation exchange is the most well‐understood framework to date. In the syntheses of bulk inorganic solids, high temperatures are generally needed to overcome the sluggish kinetics associated with solid‐solid diffusion, making the isolation of metastable species challenging, as these synthetic conditions almost invariably favor the formation of thermodynamic products [25,26] . On the nanoscale, however, cation exchange can readily occur in inorganic nanocrystals.…”

Selective kinetic growth and role of local coordination in forming Al2TiO5-based coatings at lower temperatures

“…As alternatives to solid-state synthesis methods, many solventbased and ''soft-chemical'' 40 routes have been developed. 36,41 Besides sol-gel, 42 solvothermal, 43 hydrothermal, 44,45 ion-exchange, 40,46 and various intercalation/deintercalation techniques, 47,48 they also include low-temperature chemical vapour-deposition (CVD) processes. 49,50 Rather than relying solely on the diffusion of the elements, these techniques may carry an extra degree of freedom by allowing atomic-scale control of the synthesised material through a series of step-wise polycondensations, 42,51 targeted metatheses, 37,38 and ligand reactions.…”

Expanding the I–II–V Phase Space: Soft Synthesis of Polytypic Ternary and Binary Zinc Antimonides

“…[18][19][20][21] In particular, low-temperature solutionphase reactions under kinetic control enable the synthesis and isolation of new and metastable phases. 22 For example, soft synthesis enabled control over zincblende/wurtzite polytypism in binary II-VI and III-V semiconductors. [23][24][25][26][27][28] Recently, our group successfully expanded this approach to I-II-V ternary semiconductors, where a previously unknown, cubic half-Heusler polytype of LiZnSb was synthesized for the first time.…”