Hydrothermal synthesis, structural, spectroscopic and magnetic studies of a lamellar phosphate: Ba(MnPO4)2·H2O

Abstract

Ba(MnPO ₄ ) ₂ ·H ₂ O has been prepared by hydrothermal synthesis and characterized by spectroscopic and magnetic techniques. Its crystal structure has been solved from X-ray powder diffraction data by using direct methods and refined with the Rietveld method. The compound crystallizes in the monoclinic system in the C2 space group with unit cell parameters, a = 9.457(1), b = 4.984(1), c = 8.346(1) Å and β = 92.07(1)°. The structure consists of a two-dimensional network of MnO ₆ octahedra, linked by phosphate anions and water molecules, which form chains along the |010| direction. The luminescence properties of Mn(II) in the compound are studied and the values of Dq and Racah parameters B and C have been calculated. The EPR spectra recorded on a polycrystalline sample at different temperatures show isotropic signals with g-values of 2.0. The intensity of the EPR signals increases with decreasing temperature down to 45 K and at lower temperatures rapidly decreases. Magnetic measurements show the presence of antiferromagnetic interactions. An analysis of the magnetic behaviour was carried out considering a theoretical model for antiferromagnetic chains with spin S = 5/2. Similar values for the J-exchange parameter inside the chains (J/k = –2.0 K) and for the J′-exchange parameter between neighbouring chains (zJ′/k = –2.0 K) are observed. These results suggest that the compound can be considered as a non-regular two-dimensional magnetic system.