Synthesis and characterization of a novel alkali mixed magnesium-aluminum phosphate with a layered structure–KMgAl(PO4)2

Abstract

A novel phosphate compound - potassium magnesium-aluminum double phosphate with chemical formula KMgAl(PO4)2 - has been synthesized. Platelet-shaped single crystals have been grown from the flux using K2Mo2O7 as a solvent. The powder form has been obtained through a sol-gel reaction. It has been characterized by X-ray diffraction, differential thermal analysis, vibrational spectroscopy and electronic structure calculations. KMgAl(PO4)2 crystallizes in the trigonal centrosymmetric space group P3¯m1 (No. 164) with unit cell parameters a = b = 5.347(1) Å, c = 7.903(10) Å, γ = 120° (Z = 1). The main characteristic of the crystal is the two-dimensional (2D) lamellar framework formed by Mg|AlO4 and PO4 tetrahedrons sharing their vertices of oxygen atoms, with the K+ cations located within the interlayer space. The sample morphology and chemical composition were revealed by the scanning electron microscopy – energy-dispersive X-ray spectroscopy analysis. The IR spectroscopy of KMgAl(PO4)2 confirmed the existence of a single PO4 group in agreement with the structural study. A relatively large indirect band gap of 3.86 eV was determined.