Abstract: Sodium ion conducting compositions are provided having (a) the formula Na.sub.5-x .quadrature..sub.x Gd.sub.1-y-x M.sub.y M'.sub.x Si.sub.4-z Ge.sub.z O.sub.12 whereinM is at least one of the rare earths or yttrium,M' is Zr.sup.4+, Hf.sup.4+, or Th.sup.4+,.quadrature. is a sodium vacancy to preserve charge neutrality,X is 0 to about 0.5 when Zr.sup.4+ or Hf.sup.4+ is included in M' and 0 to about 0.1 when Th.sup.4+ is included in M',y is 0 to 1, andZ is 0 to 4, with the proviso that y+x is no more than 1,And (b) the rhombohedral Na.sub.5 YSi.sub.4 O.sub.12 crystal structure with space group symmetry R3c. These compositions are useful as solid electrolytes in electrochemical cells such as galvanic cells and electrolytic cells.Certain of the sodium ion conducting compositions are novel compositions of matter.

Abstract: Substituted lithium orthosilicates are provided havingA. the formulaLi.sub.4.sub.+w.sub.-x.sub.-2y Si.sub.1.sub.-w.sub.-x.sub.-y Al.sub.w P.sub.x S.sub.y O.sub.4whereinW IS 0 TO ABOUT 0.45,X IS 0 TO ABOUT 0.5, ANDY IS 0 TO ABOUT 0.35,With the proviso that one or both of w or x+2y is at least about 0.1, andB. the monoclinic Li.sub.4 SiO.sub.4 crystal structure. These substituted orthosilicates are useful as solid electrolytes in electrochemical cells such as galvanic cells and electrolytic cells.