文摘
In this work we investigated the structural behaviour of a CaMn0.5Zr1.5(PO4)3. Due to the presence of divalent Mn2+ cations this compound can possess interesting luminescence properties. It was recently understood that this phosphate undergoes a temperature induced irreversible phase transition in the range of 800–875 °C. It has also been shown that the <em>3d–3dem> luminescence of Mn2+ increases 10 fold for the high temperature polymorph. To determine the Mn environment structural investigations of both phases have been performed by the X-ray powder diffraction and Raman spectroscopy methods. The low temperature modification adopts the trigonal <em>NZPem> structure type with a slightly lower symmetry (space group <em>Rem>32, <em>aem>=8.7850(2) Å, <em>cem>=22.6496(7) Å, <em>Vem>=1514.8(1) Å3). The high temperature form in turn has orthorhombic symmetry (space group <em>Pnma, aem>=6.2350(3) Å, <em>bem>=6.6281(3) Å, <em>cem>=14.4731(6) Å, <em>Vem>=598.13(5) Å3). Both structures were solved <em>ab-initioem> from powder data and structural analysis was performed. <em>In-situem> and RT Raman spectra are consistent with the XRD derived structural model. Mn2+ cations occupy different types of positions in these structures and a change in Mn coordination number (6 for LT phase, 7 for HT phase) results in different Mn–O bond lengths. These differences may explain the change in the optical properties between the polymorphs.