Abstract: Nitrogen-contatining rare earth melilite solid solutions of R₂Si_3-xAl_xO_3+xN_4-x(R=Nd, Sm, x=0, 0.3, 0.6, 1.0,
1.2; R=Dy, Y, x=0, 0.3, 0.6, 1.0; R=Yb, x=0, 0.3) were prepared in the temperature range from 1700℃ to 1800℃ by pressureless sintering or hot-pressing techniques. The
X-ray diffraction patterns of rare earth melilite and cell dimensions of melilite solid solutions were obtatined by using. Guinier-Hagg film data,
densitometer LS--18 and SCAN, SCANPI, PIRUM programs. The relationship between cell dimensions and actual Al contents for Nd-, Sm-, Y-melilite solid
solutions was also given. The results of measurements of cell dimensions showed that the lattice parameters of melilite solid solutions with the different rare earth elements but the same x value reduced with decreasing the ionic radii of rare
earth elements, whereas the cell dimensions became larger for melilite solid solutions with the same rare earth but increasing x values.

Key words: rare earth, melilite, X-ray diffraction