Synthesis, structural, optical, thermal, magnetic and EPR investigations of the new phosphate KCuCr(PO4)2

Abstract

New phosphate KCuCr(PO4)2 has been elaborated by solid-state reaction route and characterized by various techniques. The structure was determined from X-ray powder diffraction using Fullprof software based on Rietveld refinement. KCuCr(PO4)2 crystallizes in the monoclinic system, P21/n (no.14) space group, and with the unit cell parameter s: a = 7.861(2) Å, b = 9.828(2) Å, c = 9.002(2) Å, and β = 115.2° (1). Its structure consists of 3D - network built up from Cu2O8 units and CrO6 octahedra which construct rigid layers parallel to the bc plane. These layers connected by PO4 tetrahedra gave rise to large tunnels where K+ cations are located with nine-fold coordination. SEM analysis reveals an agglomeration state of the prepared material. DTA/TGA analysis shows good thermal stability of the crystalline powder indeed required for ceramic pigments. EPR spectrum presents a strong signal characterized a high dipole-dipole interaction (Cu2+- Cu2+, Cr3+- Cr3+ and Cu2+- Cr3+). The green color of the investigated material was mainly due to the presence of Cr3+ and Cu2+ ions in six and five-fold coordination, respectively. UV Visible spectrum consists of several bands between 400 and 850 nm, assigned to d–d transitions of Cu2+ and Cr3+ ions; besides, a strong band around 294 nm was attributed to the O–M (M = Cu, Cr) charge transfers. CIE L*a*b*and RGB parameters values were determined to examine the material's color properties as a green ceramic pigment. Magnetic measurements reveal an antiferromagnetic behavior with TN = 17 K and θCW = −128K.