Abstract
New inorganic materials have been searched in ternary system, A2O - Ln2O3- M2O5 and A2O- BO-M2O5 (Ln = Rare earths; A = Rb, K, Na and Li; B = Ca, Sr and Ba; M = Ta and Nb). Oxygen-deficient orthoniobate and fluorite-related strucrture were newly synthesized in the ternary system Rb2O- Ln2O3 - Nb2O5.