pH-controlled synthesis and spark plasma sintering of fine and homogeneous MgZr₄(PO₄)₆ powder

Abstract

MgZr₄(PO₄)₆ is an Mg²⁺ ion conductor with an isotropic three-dimensional network structure. In this study, we have examined the effect of pH adjustment on the synthesis of fine MgZr₄(PO₄)₆ powders by a sol–gel method from Mg(NO₃)₂·6H₂O, ZrCl₂O·8H₂O, and NH₄H₂PO₄. X-ray diffraction and transmission electron microscopy analyses revealed that controlling the pH at ∼10.1 during the sol–gel process was favorable for obtaining fine MgZr₄(PO₄)₆ powder, and it was also beneficial for obtaining almost single-phase sintered MgZr₄(PO₄)₆. Spark plasma sintering of the pH-controlled powder at 1200 °C for 10 min resulted in 94.1 % dense MgZr₄(PO₄)₆, which had an electrical conductivity of 8.38 × 10⁻⁴ S cm⁻¹ at 800 °C.