ChemInform Abstract: Synthesis and Characterization of the Phosphates Na_1+xMg_1+xCr_2‐x(PO₄)₃ (x = 0; 0.2) and NaZnCr₂(PO₄)₃ with the α‐CrPO₄ Structure.

Abstract

Synthesis and Characterization of the Phosphates Na 1+xMg1+xCr2-x(PO4)3 (x = 0; 0.2) and NaZnCr 2(PO4)3 with the -CrPO4 Structure. -Single crystals of Na 1.2Mg1.2Cr1.8(PO4)3 are prepared by drying (353 K, 24 h) a 6N HNO3 solution of Na2CO3, Mg(NO3)2, Cr(NO3)3, (NH4)H2PO4, and MoO3 followed by a complex heating schedule (the formed Na 2Mo2O7 is used as a flux in 3-fold molar excess; Pt crucible, 473-873 K, 24 h/stage; 1523 K, 1 h). Polycrystalline NaMgCr 2(PO4)3 and Na 1.2Mg1.2Cr1.8(PO4)3 are prepared by calcination in air of stoichiometric amounts of Na2CO3, metal nitrates, and (NH4)H2PO4 (several stages  1473 K, 24 h/stage). All compounds crystallize in the orthorhombic system (space group Imma, Z = 4, powder and single crystal XRD). The structures are closely related to the -CrPO 4 type with disordered Cr 3+ and M 2+ (M: Mg, Zn) cations. The 3D framework is built up by PO4 tetrahedra, M(1)O 6 octahedra and M(2)2O10 edge-shared double-octahedra linked through common corners and edges with Na located within tunnels. Results of EPR and magnetic susceptibility measurements indicate antiferromagnetic coupling between nearest neighbor Cr ions. At high temperature, a deviation from the Curie-Weiss law is observed which is attributed to magnetic frustration. -(SOUIWA, K.; HIDOURI*, M.; TOULEMONDE, O.; DUTTINE, M.; AMARA, M. B.; J. Alloys Compd. 627 (2015) 153-160, http://dx.