Ball milling enables phase-pure synthesis of a temperature sensitive ternary chloride, MgZrCl6

Abstract

Ball milling is a powerful synthetic tool for discovering new inorganic materials. Inspired by the high ionic conductivity in Li₂ZrCl₆ synthesized via mechanochemistry, we synthesized MgZrCl₆ with a similar method. High resolution synchrotron X-ray diffraction shows that MgZrCl₆ is poorly crystalline after ball milling, but crystallizes in a layered hexagonal structure (P31c) after heat treatment. In situ synchrotron X-ray diffraction reveals a narrow temperature window around 400 °C in which crystallization occurs. At higher temperatures the phase decomposes. Pair distribution function analysis shows 2D sheets of MgZrCl₆ form after milling, with heating driving 3D crystallization. Raman spectroscopy also shows evidence of MgZrCl₆ after milling. Electrochemical impedance spectroscopy does not reveal ionic conductivity in MgZrCl₆ (limit of detection ca. 1.4 × 10^-8 S/cm). In addition to supporting existing design rules for Mg-based solid electrolytes, this work shows the power of ball milling to synthesize temperature-sensitive inorganic compounds with high yield.