Kinetic aspects of the synthesis of Ln(6-x)MoO(12-delta) (Ln = Sm, Ho -Yb; x=0, 0.5) rare-earth molybdates using mechanical activation of oxides

摘要

The synthesis of the Ln(6)MoO(12) (Ln = Sm, Ho -Yb) (3:1) rare-earth molybdates from binary oxides at room temperature has been studied by XRD and electron spin resonance spectroscopy (ESR). The mechanical activation of 3Ln(2)O(3) + MoO3 (Ln = Sm, Ho, Yb) mixtures containing unmilled or premilled MoO3 initiates the formation of Lri(6)MoO(12) (Ln = Sm, Ho-Yb) at room temperature, which is accompanied by a reduction in the ESR signal from Mo5+ paramagnetic ions located on the surface of the activated Mo03 and, hence, by a reduction in the amount of MoO3 in the mixture, due to reaction with Ln(2)O(3) (Ln = Sm, Ho, Yb).The major phase resulting from the mechanochemical synthesis is a cubic phase with the bixbyite structure (la(-3), no. 206) for Ln(6-x)MoO(12-delta) (Ln = Dy -Yb; x = 0, 0.5) and the Sm2O3 type structure (C 2/m, no. 12) for Ln(6)MoO(12) (Ln = Gd, Sm).