Selective Octahedral Accommodation of Cr$^{3+}$ and Weak Magnetic Connectivity in the Sugilite Analogue KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$

Abstract

We report the synthesis of the Cr analogue of sugilite, KNa$_2$Cr$_2$Li$_3$Si$_{12}$O$_{30}$, in the milarite-type framework. Rietveld refinement of a composition-conserving antisite model gives $x = 0.0024(18)$ in KNa$_2$[Cr$_{2-x}$Li$_x$][Li$_{3-x}$Cr$_x$]Si$_{12}$O$_{30}$, corresponding to a T2-site Cr occupancy of $0.0008(6)$. X-ray MEM analysis shows no detectable Cr-like density at T2. Magnetic susceptibility indicates weak antiferromagnetic interactions with $θ_{\mathrm{W}} = -4.78(7)$ K and no ordering above 1.8 K.