Mechanochemical synthesis of LaOX(X= Cl, Br) and their solid state solutions

A mixture of lanthanum oxide (La2O3), chloride (LaCl3), and bromide (LaBr3) was ground in air by a planetary ball mill to investigate synthesis of lanthanum oxychloride (LaOCl), oxybromide (LaOBr), and their solid solutions, LaOCl1-xBrx (0 less than or equal to x less than or equal to 1, Deltax = 0.25). The synthesizing reactions proceed with an increase in grinding time. Unit cell dimensions, a, c, and lattice volume of the solutions evolve linearly with an increase in x in the LaOCl1-xBrx series. Comparing unit cell dimensions of LaOX synthesized by mechanochemical reaction to those of LaOX synthesized by solid-state reaction at high temperature, there is no difference in the length of c, while a is shortened slightly. This may be attributed to the complex cation layer of (LaO)(n)(n+), with a close relationship to a of the cell dimensions, being affected by the intensive grinding. (C) 2001 Academic Press.