Controlled atmosphere process for altering the nonstoichiometry of crystalline members
AssigneeXerox Corporation
InventorRobert L. Holman
Life of this patent
Estimating the term…
Abstract
The nonstoichiometry of a crystalline member is altered by promoting conditions of vapor phase equilibrium between the member and a slotted crucible in which it is placed. The slotted crucible comprises material sharing a common vapor species with the crystalline member and provides an atmosphere of substantially constant thermodynamic activity with respect to the shared vapor phase upon isothermal heating of the member and crucible. In one embodiment, by achieving a partial vapor phase equilibration between a transparent crystalline member and such a crucible both the magnitude and profile of the refractive index of the member near its surfaces is modified in a controlled member.
Claims20
A method for altering the stoichiometry of a single phase crystalline solid, comprising:
- a. placing said crystalline solid within a solid crucible having a cavity of pre-determined dimensions such that said crystalline solid is substantially symmetrically separated from the walls of said cavity in said solid crucible by a distance up to about three millimeters, said crucible comprising material which gives off the same chemical metal component in the vapor phase as said crystalline solid at a temperature, T;
- said chemical component in the vapor phase having a vapor pressure less than about 10.sup.-4 atmosphere at said temperature T;
- and
- b. isothermally heating said crystalline solid and said solid crucible at said temperature T, to surround said crystalline solid with an atmosphere of substantially constant activity with respect to said chemical component in the vapor phase and within said cavity;
- said pre-determined dimensions of said cavity being effective to produce mass transport between said crystalline solid and said solid crucible under vapor phase equilibrium conditions.
A method for forming a waveguiding layer in a transparent crystalline member comprising:
- a. placing said transparent crystalline member in a crucible having a cavity of predetermined dimensions such that said crystalline solid is substantially symmetrically separated from the walls of said cavity in said solid crucible by a distance up to about 3 millimeters comprising material which gives off the same chemical metal component in the vapor phase as said transparent crystalline member at a temperature, T;
- said chemical component in the vapor phase having a vapor pressure less than about 10.sup.-4 atmosphere at said temperature T;
- and
- b. isothermally heating said transparent crystalline member and said crucible at said temperature, T, to provide an atmosphere surrounding said transparent sample and of substantially constant activity with respect to said chemical component in the vapor phase, for a period of time sufficient to form along the surface of said transparent crystalline member a layer region thereof having an optical index of refraction greater than the optical index of refraction of the remaining bulk of said transparent crystalline member.
Dependencies are inferred from the claim text.