Experimental and theoretical investigation of a mesoporous KxWO3 material having superior mechanical strength

Abstract

Mesoporous materials with tailored properties hold great promise for energy harvesting and industrial applications. We have synthesized a novel tungsten bronze mesoporous material (K_xWO₃; x ∼ 0.07) having inverse FDU-12 type pore symmetry and a crystalline framework. In situ small angle X-ray scattering (SAXS) measurements of the mesoporous K_0.07WO₃ show persistence of a highly ordered meso-scale pore structure to high pressure conditions (∼18.5 GPa) and a material with remarkable mechanical strength despite having ∼35% porosity. Pressure dependent in situ SAXS measurements reveal a bulk modulus κ = 44 ± 4 GPa for the mesoporous K_xWO₃ which is comparable to the corresponding value for the bulk monoclinic WO₃ (γ-WO₃). Evidence from middle angle (MAXS) and wide angle X-ray scattering (WAXS), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy shows that the presence of potassium leads to the formation of a K-bearing orthorhombic tungsten bronze (OTB) phase within a monoclinic WO₃ host structure. Our ab initio molecular dynamics calculations show that the formation of the OTB phase provides superior strength to the mesoporous K_0.07WO₃.