Glass-ceramics of the aluminum or gallium, and phosphorus-containing Na5SmSi4O12-type Na+-superionic conductors (N5SXPS) were prepared by crystallization of glasses with the composition Na3 + 3x - y + zSm1 -xXzPySi3 - y - zO9 (X=Al; NSAPS, X= Ga; NSGPS), and the effects of X elements on the separation of the phase and the microstructural effects on the conduction properties of glass-ceramics were discussed. N5SXPS was obtained as a stable phase at high temperatures. The ionic conductivities of NSAPS and NSGPS were 0.67 x 10(-1) and 0.76 x 10(-1) S/cm at 300 degreesC, respectively. (C) 2004 Elsevier B.V. All rights reserved.