STRUCTURE AND SOME PROPERTIES OF THE PREVIOUSLY UNKNOWN YTTERBIUM SILICATE A-YB2SIO5

Nonisothermal oxidation of ytterbium N-woehlerite (Yb4Si2O7N2), also k nown as the J-phase, has revealed a previously unknown and possibly un stable modification, Yb2SiO5. The phase is isostructural with the A ty pe modification (RE)(2)SiO5 (RE = rare earth). A new crystallographic description is provided for the detected phase and thermal stability d ata are compared with such data available for analogous RE compounds. The results indicate that oxidation of RE oxynitrides may produce meta stable phases of the type (RE)(4)Al2(1-x)Si-2x. O9+x or phases that ca nnot be prepared by standard methods because their low-temperature sta bility range is so narrow.